|Publication number||US6895452 B1|
|Application number||US 09/174,057|
|Publication date||May 17, 2005|
|Filing date||Oct 16, 1998|
|Priority date||Jun 4, 1997|
|Also published as||US20050114560|
|Publication number||09174057, 174057, US 6895452 B1, US 6895452B1, US-B1-6895452, US6895452 B1, US6895452B1|
|Inventors||Ron Coleman, Brent LeBack, Stuart Hawkinson, Richard Rubinstein|
|Original Assignee||Marger Johnson & Mccollom, P.C.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (20), Non-Patent Citations (5), Referenced by (18), Classifications (19), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part of application Ser. No. 08/869,277, filed Jun. 4, 1997, is now abandoned, and is incorporated herein by reference. This application also claims the priority date of provisional application Ser. No. 60/062,431, filed Oct. 16, 1997.
The present invention is generally in the field of digital computer architectures and, more specifically, is directed to an architecture where an execution unit is tightly coupled to a shared reconfigurable memory.
General purpose microprocessor cores are known for implementation into integrated circuits for a wide variety of applications. Specialized computation engines which are specifically adapted to perform complex computational algorithms, such as Digital Signal Processing (DSP), are also known. DSP cores are specialized computation engines for carrying out digital signal processing tasks which are specially configured to efficiently process DSP algorithms. An example of a known DSP chip is the DSP 56002 processor, commercially available from Motorola. In order to achieve improved performance in DSP-related processing, the conventional approach is to combine a general purpose processor core together with a DSP core. The general purpose processor carries out Input/Output (I/O) tasks, logic functions, address generation, etc. This is a workable but costly solution. Additionally, evolving new applications require increasing amounts of memory and the use of multiple conventional digital signal processors. Additionally, power dissipation becomes a limiting factor in hardware of this type. The challenge, therefore, is to provide for improvements in processing performance while containing or reducing costs.
In view of the foregoing, one object of the present invention is to provide an improved computer architecture that utilizes available memory more efficiently in DSP and other specialized processor systems. Another object is to reduce the power consumption and size of computational processing systems.
A further object of the present invention is to provide for shared and reconfigurable memory in order to reduce I/O processor requirements in processor and co-processor architectures. A further object is to extend a shared, reconfigurable memory architecture to multiple memory blocks and execution units.
Another object of the present invention is to provide for microcode programming of a memory system controller in order to provide for dynamic reconfiguration of reconfigurable memory. A further object of the invention is to provide improvements in memory addressing methods, architectures and circuits for continuous execution together with simultaneous, continuous Direct Memory Access (DMA) operations.
A still further object of the invention is to provide improvements in execution units for computational operations, for example execution unit architectures that feature deep-pipeline structures and local registers, and that support parallel operations. Modified execution units can be used to improve efficiency of operation in conjunction with reconfigurable memory.
Yet another object of the present invention is a “virtual two port” memory structure based on a conventional, single-port memory cell. Yet another object is to provide for implementation in both Static Random Access Memory (SRAM) and Dynamic Random Access Memory (DRAM) configurations of the virtual two-port memory.
In view of the foregoing background, the present invention is directed to improved hardware architectures for improved access to a memory array and, more specifically, is directed to “memory-centric” methods and apparatus for improved performance in the interface between a memory array and high speed computational engines, such as digital signal processing or “DSP” systems. As mentioned above, improvements in computational performance have been achieved by providing special arithmetic units or “execution units” that are optimized to carry out the arithmetic operations that are commonly required by complex algorithms—mainly multiplication and addition—at very high speed. One example of such an execution unit is the “DAU” (data execution unit) provided in the WE DSP32C chip from AT&T, for DSP applications. The AT&T execution unit, and others like it, provide relatively fast, floating point arithmetic operations to support computation-intensive applications such as speech, graphics and image processing.
While many improvements have been made in floating-point execution units, pipelined architectures, decreased cycle times, etc., known computational systems generally utilize standard memory systems. For example, DRAM integrated circuits are used for reading input data and, on the output side, for storing output data. Operand and result data is moved into and out of the DRAM memory systems using known techniques such as multiple-ported memory, DMA hardware, buffers, and the like. While such systems benefit from improvements in memory speed and density, data transfer at the memory interface remains a relative bottleneck. I have reconsidered these known techniques and discovered that significant gains in performance and flexibility can be achieved by focusing on the memory, in addition to the execution unit, and by providing improvements in methods and circuits for moving data efficiently among data sources (such as a host processor bus or I/O channel), memory subsystems, and execution units. Since the focus is on the memory, I coined the term “memory-centric” computing.
One aspect of the present invention is a Memory-Centric Controller (MCC) which includes a microcode store, microcode sequencer and memory configuration control circuit whereby the MCC is able to dynamically reconfigure a reconfigurable memory array responsive to microcode programs stored within the microcode store. The microcode sequencer controls execution of the microcode program to generate microcode control words which drive the memory configuration control circuit. The memory configuration control circuit, in turn, generates a memory configuration control signal which is output to the memory array in order to dynamically modify the configuration of the memory array under microcode control.
Importantly, the memory array is readily “reconfigurable” so that it can be adapted to the requirements of particular applications. Reconfiguration can include dividing the memory array into several blocks which are independently accessible through data I/O ports connected to the memory array. The memory blocks can also be reconfigured both in depth, i.e. number or words or rows, as well as in width (word size). This flexibility simplifies, and speeds, memory I/O for various applications, and provides great flexibility for creating specialized computational systems, which can be implemented as stand-along systems for embedded applications, or as separate “co-processors” or “on-board” devices with a general purpose or other core processor. For example, the memory word size can be easily configured to match that of an I/O channel or execution unit currently in use. The invention can be implemented in both von Neumann as well as Harvard architectures.
The invention further anticipates the use of an execution unit in concert with the reconfigurable memory array where the execution unit is controlled by the MCC and reconfigured in several ways, including selectable depth (number of pipeline stages) and width (i.e. multiple word sizes concurrently). Preferably the pipelined execution unit(s) includes internal register files with feedback. In this aspect of the invention, the MCC includes an execution address generator and an opcode generator which operate under microcode control. The execution address generator generates an execution address signal that is output to the memory array in order to obtain operands for the execution unit from data in the memory array and store the result data produced from the execution unit back in the memory array. The opcode generator outputs opcodes which control both the configuration and function of the execution unit. Thus, both the memory array and execution unit are dynamically reconfigurable under microcode control in order to optimize the data path from the memory array, through the execution unit, and back to the memory array for the particular algorithm implemented in the microcode program.
The microcode program can be included in non-volatile memory attached to the MCC, initialized by the MCC from non-volatile memory, downloaded to the MCC by the host core processor, and/or updated under software control. This combination of reconfigurable memory, together with reconfigurable execution units, the associated techniques for efficiently moving data between them, and the flexibility of microcode programming provides an architecture that is highly flexible.
Microcoded software can be used to take advantage of this architecture so as to achieve new levels of performance in memory and computation systems. The microcode and architecture can be optimized for a variety of embedded applications because the same underlying hardware is reconfigurable under microcode control for a particular application. When the MCC is paired with a core processor or host system, however, microcode programs can be downloaded as needed to perform each function desired by the host processor or system with the architecture being reconfigurable for each function so as to achieve high levels of performance.
In one embodiment of the present invention, an execution architecture is composed of a memory array having first and second blocks, first and second I/O ports, first and second address ports, and a configuration control port. A first value of a configuration control signal received at the configuration control port configures the first block to be coupled to the first I/O port and the first address port and the second block to be coupled to the second I/O port and the second address port. A second value of the configuration control signal configures the first block to be coupled to the second I/O port and the second address port and the second block to be coupled to the first I/O port and the first address port. The architecture includes a data controller and address generator (DCAG) having an address output port and a control input port, the address output port of the DCAG being coupled to the first address port of the memory array and the DCAG being configured to generate address values at the DCAG address output port responsive to a vector data control signal received at the DCAG control input port. A DMA controller and address generator (DMACAG) has an address output port and a control input port, where the address output port of the DMACAG is coupled to the second address port of the memory array and the DMACAG is configured to generate address values at the DMACAG address output port responsive to a DMA control signal received at the DMACAG control input port. A first execution unit has first and second I/O ports, the first I/O port of the first execution unit being coupled to the first I/O port of the memory array. A first local memory array has a first I/O port and a first address port, the first I/O port of the first local memory being coupled to the second I/O port of the first execution unit. And a first local address generator (LAG) has an address output port and a control input port, the address output port of the first LAG being coupled to the first address port of the first local memory array and the first LAG being configured to generate address values at the first LAG address output port responsive to a first execution control signal received at the first LAG control input port.
This architecture above provides a fast memory path through the execution unit, local memory and local address register than is not dependent upon the typically slower data path to the memory array. This allows fast scalar operations to be performed in the local memory by the execution unit while vector operations flow through the memory array. The architecture also provides for fast saving and restoring of process states in the execution unit during context switches. It also permits the execution unit to be used to rapidly generate and store coefficients in local memory for certain operations, such as DSP operations.
Another aspect of the architecture of the present invention includes a memory centric controller (MCC) configured to generate the configuration control signal, the vector data control signal, the DMA control signal and the first execution control signal. The MCC is configured to switch the first and second blocks of the memory array and drive the DCAG and DMACAG independently of one another to simultaneously transfer data through the first and second I/O ports of the memory array and the MCC is configured to independently drive the first LAG to transfer data between the first local memory and the first execution unit.
This architecture permits a DMA bus transfer operation to take place simultaneously to a vector processing operation. The blocks of the memory array are then swapped under MCC control to allow the data input during the DMA operation to be vector processed while the vector processed data is streamed out of memory and replace with new input data. The configuration control signal, the vector data control signal, the DMA control signal and the first execution control signal can also be microcode values generated by the MCC.
Another embodiment of the architecture includes an execution unit interface unit interposed the execution unit and the memory array and having a first I/O port coupled to the first I/O port of the execution unit and a second I/O port coupled to the first I/O port of the memory array, a control input port configured to receive an execution unit interface control signal, and a first wide buffer. A first predetermined number of words of the first wide buffer is proportional to a ratio of an execution speed of the execution unit to an access speed of the memory array and the execution unit interface unit transfers individual words of data between the execution unit and the first wide buffer and transfers the first predetermined number of words between the first wide buffer and the memory array responsive to the execution unit interface control signal.
This embodiment of the architecture permits data to be transferred between the execution unit and the memory array without delays for the slower of the two interfaces. Typically, the access speed of the memory array is much slower than the execution speed of the execution unit. The execution interface unit, transfers data words between the wide buffer and the execution unit and transfers the contents of the entire wide buffer to and from the memory array. For example, if the execution unit is operating with 64 bit words at 200 MHz and the memory array operates at 25 MHZ, then the wide buffer size is 512 bits. Similar speed matching can be obtained for bus transfers using a bus interface unit coupled between the memory array and a system bus.
Yet another aspect of the present architecture includes a second local address generator (LAG) having an address output port and a control input port. The second LAG being configured to generate address values at the second LAG address output port responsive to a second execution control signal received at the second LAG control input port. The first local memory includes first and second blocks, a second I/O port, a second address port and a configuration control input. Responsive to a first value of a local memory configuration control signal received at the configuration control input, the first block of the first local memory is coupled to the first I/O port and first address port and the second block of the first local memory is coupled to the second I/O port and second address port. Responsive to a second value of the local memory configuration control signal, the first block of the first local memory is coupled to the second I/O port and second address port and the second block of the first local memory is coupled to the first I/O port and first address port, the address output port of the second LAG being coupled to the second address port of the first local memory.
This aspect of the architecture permits a microcode program pertaining to a first execution unit operation to be loaded into one block of local memory and operated while a microcode program pertaining to a second execution unit operation is loaded into the other block of local memory. The blocks are then switched by reconfiguring the memory and the second execution unit operation proceeds while yet another microcode program is loaded into the first block of local memory. This provides for fast operation of the execution unit for a variety of types of operations with minimal delay between operations and, most importantly, the use of a slow, large micro-code store in the MCC, e.g., flash memory, ROM, DRAM, wherein the local memories for micro-code supporting the execution units at high speed have smaller memory requirements than larger, slower memory units in the MCCU, and have faster speed.
Multiple execution units can be added to the present architecture to simultaneously perform different functions. In still another aspect of the present execution architecture, the memory array includes a third block coupled to a third I/O port and a third address port of the memory array, wherein the third block of the memory array is configured to be switched with the first and second blocks of the memory array responsive to the configuration control signal. This aspect of the architecture includes another data controller and address generator (DCAC) having an address output port and a control input port, the address output port of the another DCAG being coupled to the third address port of the memory array and the DCAG being configured to generate address values at the DCAG address output port responsive to another vector data control signal received at the second DCAG control input port. A second execution unit has first and second I/O ports, the first I/O port of the first execution unit being coupled to the third I/O port of the memory array. A second local memory array has an I/O port and an address port, the I/O port of the second local memory being coupled to the second I/O port of the second execution unit. And a second local address generator (LAG) has an address output port and a control input port, the address output port of the second LAG being coupled to the address port of the second local memory array and the second LAG being configured to generate address values at the second LAG address output port responsive to a second execution control signal received at the second LAG control input port.
This aspect of the present architecture provides for multiple execution units that simultaneously perform different operations, such as a codec operation in one execution unit and a motion estimation operation in another execution unit. The present architecture can be scaled to provide the number of execution units needed to perform a given function. For example, the architecture can include three execution units to perform motion estimation and one execution unit to act as a codec (coder/decoder). The architecture is therefore particularly suited for a computationally intensive application such as an MPEG-2 encoder.
In still another embodiment of the present architecture, the first execution unit includes a combination multiplier/arithmetic logic unit (ALU) block having first and second input ports and an output port, and a vector register file. The vector register file has a first I/O port coupled to the first I/O port of the first local memory, a second I/O port coupled to the first I/O port of the memory array, a first output port coupled to the first input port of the ALU, a second output port coupled to the second input port of the ALU, and a first input port coupled to the output port of the ALU. In addition, the vector register file has a first output port coupled to the first input port of a combination multiplier/ALU block, a second output port coupled to the second input port of the combination multiplier/ALU block, and a first input port coupled to the output port of the combination multiplier/ALU block. The vector register file includes multiple register blocks configured to be independently coupled to the first and second I/O ports, the first and second output ports and the input port of the vector register file responsive to a vector register control signal. A word size of each of the multiple blocks is independently configurable by the vector register control signal to match a transfer rate of each of the ports of the vector register file.
The vector register file includes multiple memory blocks that can be controlled by an MCC and multiple address generators. Each block can operate independently to feed a different port at a rate and word size appropriate for the transfer rate of the device coupled to the port. This allows multiple operations to be implemented in the register and executed concurrently. The vector register can be interfaced to the memory array, which is typically a DRAM array, by physically connecting bidirectional signal wires from sense amps and write drivers within the memory array. This aspect of the architecture allows data words from a fast local memory to be driven into a separate port of the vector register and then out to the arithmetic logic unit at high speed while a larger data buffer is simultaneously transferred from the memory array into the vector register file.
The present invention is useful in a wide variety of computational and signal processing applications including programmable MPEG-2 encoder and decoder, graphics, speech processing, image processing, array processors, etc. In telecommunications, the invention can be used, for example, for switching applications in which multiple I/O channels are operated simultaneously.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.
Because the present invention may be integrated into an existing processor or controller core design, so that both the core processor and the present invention reside in the same integrated circuit, reference will be made herein to the core processor meaning the processor that the present invention has been attached to or integrated with.
In operation, the interface 44, 46 to the two-port memory block A is a DMA interface that is in communication with the host processor or controller 40. Block A receives data coefficients and optionally other parameters from the controller, and also returns completed data to the controller that results from various DSP, graphics, MPEG-2 encoder/decoder or other operations carried out in the execution unit 90. This output data can include, for example, FFT results, or convolution data, or graphics rendering data, etc. Thus the single memory can alternately act as both a graphics frame buffer and a graphics computation buffer memory.
Concurrently, the memory block “B” (60) interfaces with the functional execution unit 90. The functional execution unit 90 receives data from the two-port memory block B and executes on it, and then returns results (“writeback”) to the same two-port memory structure. The source address generator 70 supplies source or input data to the functional execution unit while the destination address generator 80 supplies addresses for writing results (or intermediate data) from the execution unit to the memory. Put another way, source address generator 70 provides addressing while the functional execution unit is reading input data from memory block B, and the destination address generator 80 provides addressing to the same memory block B while the functional execution unit 90 is writing results into the memory.
As mentioned above, when the execution unit has completed its work on the data in block B, the memory effectively “swaps” blocks A and B, so that block B is in communication with the DMA channel 42 to read out the results of the execution. Conversely, and simultaneously, the execution unit proceeds to execute on the new input data in block A. This “swapping” of memory blocks includes several aspects, the first of which is switching the memory address generator lines so as to couple them to the appropriate physical block of memory.
In an alternative embodiment, the system can be configured so that the entire memory space (blocks A and B in the illustration) are accessed first by an I/O channel, and then the entire memory swapped to be accessed by the processor or execution unit. In general, any or all of the memory can be reconfigured as described. The memory can be SRAM, DRAM or any other type of random access semiconductor memory or functionally equivalent technology. DRAM refresh is provided by address generators, or may not be required where the speed of execution and updating the memory (access frequency) is sufficient to obviate refresh.
Two bits are sufficient here to illustrate the concept without unduly complicating the drawing. The source address generator 70 is coupled to both memory blocks A and B. In block B, the top row includes a series of cells including bit cell 62. In fact, the source address generator preferably has output lines coupled to all of the rows of not only block B, but block A as well, although only one row line is illustrated in block A. Note also that corresponding address lines from the AG 70 and the DMA 102 are shown as connected in common, e.g. at line 69. However, in practice, these address lines are selectable as described above with reference to FIG. 2.
A destination address generator 80 similarly is coupled to the row lines of both blocks of memory. Memory cells 62 and 64 are full two-ported cells on the same column in this example. Thus, either source AG 70 or DMA 102 address the left port, while either destination AG 80 or DMA 100 address the right port. A write select multiplexer 106 directs data either from the DMA (42 in
DMA address generator 102 addresses memory block B (60) during T0 cycles. This is indicated by the left (T0) portion of DMA AG 102. During T1 cycles, DMA address generator 102 addresses memory block A (50), as indicated by the right portion of 102. During T1, DMA AG 102 also receives setup or configuration data in preparation for again addressing Mem Block B during the next T0 cycle. Similarly, during T0, DMA 102 also receives configuration data in preparation for again addressing Mem Block A during the next T1 cycle.
During a T0 cycle, the functional execution unit (90 in
At the beginning of a T1 cycle, memory blocks A and B effectively swap such that execution unit 90 will process the data in memory block B 60 under control of execution address generator 70 and data will stream into memory block A 50 under control of DMA address generator 102. Conversely, at the beginning of a T0 cycle, memory blocks A and B again effectively swap such that execution unit 90 will process the data in memory block A 50 under control of execution address generator 70 and data will stream into memory block B 60 under control of DMA address generator 102.
The preferred architecture for implementation in a processor application, as distinguished from a coprocessor application, is illustrated in
Bit Configuration Tables
Essentially, the bit configuration table is used to generate configuration control signal 152 which determines the position of virtual boundary 136 and, therefore, the configuration of memory blocks A and B. It also provides the configuration information necessary for operation of the address generator 170 and the DSP execution unit 130 during the T1 execution cycle time. Path 174 illustrates the execution unit/memory interface control signals from the bit configuration table 140 to the DSP execution unit 130. Path 176 illustrates the configuration control signal to the execution unit to reconfigure the execution unit. Path 178 illustrates the op codes sent to execution unit 130 which cause execution unit to perform the operations necessary to process data. Path 188 shows configuration information loaded from the configuration tables into the address generator 170.
The architecture illustrated in
Memory-Centric DSP Controller
A DSP process initiated in MDSPC 172 then generates the appropriate memory configuration control signals 152 and execution unit configuration control signals 176 based upon the downloaded microcode to control the position of virtual boundary 136 and structure execution unit 130 to optimize performance for the process corresponding to the microcode. As the DSP process executes, MDSPC 172 generates addresses for memory block B 160 and controls the execution unit/memory interface to load operands from memory into the execution unit 130 which are then processed by execution unit 130 responsive to op codes 178 sent from MDSPC 172 to execution unit 130. In addition, virtual boundary 136 may be adjusted responsive to microcode during process execution in order to dynamically optimize the memory and execution unit configurations.
In addition, the MDSPC 172 supplies the timing and control for the interfaces between memory and the execution unit. Further, algorithm coefficients to the execution unit may be supplied directly from the MDSPC. The use of microcode in the MDSPC results in execution of the DSP process that is more efficient than the frequent downloading of bit configuration tables and address parameters associated with the architecture of FIG. 5A. The microcoded method represented by the MDSPC results in fewer bits to transfer from the core processor to memory for the DSP process and less frequent updates of this information from the core processor. Thus, the core processor bandwidth is conserved along with the amount of bits required to store the control information.
Similar to the embodiments shown in
The bit tables and microcode discussed above may alternatively reside in durable store, such as ROM or flash memory. The durable store may be part of memory block A or may reside outside of memory block A wherein the content of durable store is transferred to memory block A or to the address generators or MDSPC during system initialization.
Furthermore, the DSP process may be triggered by either decoding a preselected bit pattern corresponding to a DSP function into an address in memory block A containing the bit tables or microcode required for execution of the DSP function. Yet another approach to triggering the DSP process is to place the bit tables or microcode for the DSP function at a particular location in memory block A and the DSP process is triggered by the execution of a jump instruction to that particular location. For instance, at system initialization, the microcode to perform a DSP function, such as a Fast Fourier Transform (FFT) or IIR, is loaded beginning at a specific memory location within memory block A. Thereafter, execution of a jump instruction to that specific memory location causes execution to continue at that location thus spawning the DSP process.
Referring now to
Referring again to
In regard to
In the embodiment of
The DSP Instruction Decode 222 may be reduced or eliminated if the DSP process is initiated by an instruction causing a jump to the bit table or microcode in memory block A pertaining to the execution of the DSP process.
To summarize, the present invention includes an architecture that features shared, reconfigurable memory for efficient operation of one or more processors together with one or more functional execution units such as DSP execution units.
Reconfigurable Memory Architecture
The large vertical arrows in
Additional “configuration control bits” are shown to the left of dashed line 267. This extended portion of the memory can be used for storing a bit configuration table that provides configuration control bits as described previously with reference to the bit configuration table 140 of
The configuration control bits shown in
When the MDSPC of
The address lines that control the reconfigurable portion of the memory are switched between the DMA address source 102 and address generator 104 via switching means 296. Illustrative switching means for addressing a single block of memory from multiple address generators was described above, for example with reference to FIG. 2. The particular arrangement depends in part on whether the memory is single-ported (see
It should be noted that the entire block need not be switched in toto to one memory block or the other. Rather, the reconfigurable block preferably is partitionable so that a selected portion (or all) of the block can be switched to join the upper or lower block. The granularity of this selection (indicated by the dashed lines in 280) is a matter of design choice, at a cost of additional hardware, e.g. sense amps, as the granularity increases, as further explained later.
For each row of the memory 300, the corresponding address lines from the source and destination blocks 310, 312, are logically “ORed” together, as illustrated by OR gate 316, with reference to the top row of the memory comprising memory cell 302. Only one row address line is asserted at a given time. For writing to the memory, a multiplexer 320 selects data either from the DMA or from the execution unit, according to a control signal 322 responsive to the configuration bits, in the source address generator 310. The selected data is applied through drivers 326 to the corresponding column of the memory array 300 (only one column, i.e. one pair of bit lines, is shown in the drawing). For each column, the bit lines also are coupled to a sense amplifier 324, which in turn provides output or write data to the execution unit 326 and to the DMA 328 via path 325. The execution unit 326 is enabled by an execution enable control signal responsive to the configuration bits 330 in the destination address block 312. Configuration bits 330 also provide a DMA control enable signal at 332.
The key here is to eliminate the need for a two-ported RAM cell by using a logical OR of the last addresses from the destination and source registers (located in the corresponding destination or source address generators). Source and destination operations are not simultaneous, but operation is still fast. A source write cycle followed by a destination read cycle would take only a total time of two memory cycles.
FIG. 12. The techniques and circuits described above for reconfigurable memory can be extended to multiple blocks of memory so as to form a highly flexible architecture for digital signal processing.
The bit lines, for example bit line pair 410, extend through the memory array segment to a second write select circuit 420. This circuit selects the input source to the second memory segment 460. If the select circuit 420 selects the bit lines from memory segment 400, the result is that memory segment 400 and the second memory segment 460 are effectively coupled together to form a single block of memory. Alternatively, the second select circuit 420 can select write data via path 422 from an alternative input source. A source select circuit 426, for example a similar multiplexer circuit, can be used to select this input from various other sources, indicated as M2 and M1. When the alternative input source is coupled to the second memory segment 460 via path 422, memory segment 460 is effectively isolated from the first memory segment 400. In this case, the bit lines of memory segment 400 are directed via path 430 to sense amps 440 for reading data out of the memory segment 400. When the bitlines of memory segment 400 are coupled to the second segment 460, sense amps 440 can be sent to a disable or low power standby state, since they need not be used.
Similarly, a second segment of memory M2 provides read data via path 542 to execution unit A and via path 540 to execution unit B. Output data or results from execution unit B are provided via path 544 to both MUX-1 and to MUX-2. MUX-2 provides selected write data into the memory block M2. In this way, data can be read from either memory block into either execution unit, and results can be written from either execution unit into either memory block.
A first source address generator S1 provides source addressing to memory block M1. Source address generator S1 also includes a selection table for determining read/write configurations. Thus, S1 provides control bit “Select A” to MUX—1 in order to select execution unit A as the input source for a write operation to memory M1. S1 also provides a “Select A” control bit to MUX-2 in order to select execution unit A as the data source for writing into memory M2.
A destination address generator D1 provides destination addressing to memory block M1. D1 also includes selection tables which provide a “Read 1” control signal to execution A and a second “Read 1” control signal to execution unit B. By asserting a selected one of these control signals, the selection bits in D1 directs a selected one of the execution units to read data from memory M1.
A second source address generator S2 provides source addressing to memory segment M2. Address generator S2 also provides a control bit “select B” to MUX-1 via path 550 and to MUX-2 via path 552. These signals cause the corresponding multiplexer to select execution unit B as the input source for write back data into the corresponding memory block. A second destination address generator D2 provides destination addressing to memory block M2 via path 560. Address generator D2 also provides control bits for configuring this system. D2 provides a read to signal to execution unit A via path 562 and a read to signal to execution unit B via path 564 for selectively causing the corresponding execution unit to read data from memory block M2.
Note, however, that the choice of one half block increments for the illustration above is arbitrary. Segmentation of the memory may be designed to permit reconfigurability down to the granularity of words or bits if necessary.
The use of multiple sense amps for memory segment configuration was described previously with reference to
FIG. 20. is a block diagram illustrating a memory system of multiple configurable memory segments having multiple sense amps for each segment. This alternative can be used to improve speed of “swapping” read data paths and reduce interconnect overhead in some applications.
MCC 172 contains a sequence controller 700 which sequences through a microcode routine stored in microcode store 710. Sequence controller 700 functions in a manner similar to conventional sequencers which are found in a wide variety of applications and which sequence through a set of control instructions in order to control a variety of functional units external to the controller and redirect program flow responsive to microcode instructions and feedback from the external functional units.
However, sequence controller 700 differs from conventional sequencers in its use of a microcode control word for memory centric applications. Memory centric control words include DMA-I/O addresses, execution addresses, opcodes for execution units, reconfiguration and configuration control bits for memory configuration, and latch timing and control for memory interfaces and pipeline control between the memory and execution units.
Microcode store 710 may take a number of forms and be populated in various ways depending upon the context within which the MCC will operate. For instance, microcode store 710 can include read-only memory (ROM), such as EEPROM, flash memory and other forms of non-volatile storage, which contains all or part of the microcode routines to be executed by MCC 172. Alternatively, microcode store 710 may include volatile memory, such as DRAM or SRAM, which is initialized at power-up by an initialization routine contained within a bootstrap memory also included within microcode store 710, that downloads microcode routines from non-volatile storage. These examples would typically be present in an embedded application where the MCC 172 is, at least in part, an independently functioning processor which executes a relatively narrow set of functions.
In the context where MCC 172 is teamed with a core processor, the microcode can be downloaded under control of the core processor. This requires that microcode store 710 be accessible to the core processor, in addition to the sequence controller 700, but provides for greater flexibility and broader range in the functions performed by MCC 172 because a microcode program is downloaded for the specific task required by the core processor, which allows the code to be optimized for the particular function, rather than being adapted for more general functionality, and also allows the use of customized routines developed by a user of the MCC 172.
Alternatively, MCC 172 can configure a portion of memory 800 to contain the microcode instructions and eliminate the need for a separate microcode store 710. However, the overhead involved in downloading the microcode from the core processor to microcode store 710 for each task is likely to be small relative to the time required to process a block of data. The overhead for download, in turn, may be reduced by structuring the microcode to have subroutines shared by a number of higher level functions so that only the microcode specific to the higher level function need be downloaded for a particular task. In this case, the microcode will include a library of routines and subroutines shared by the higher level functions.
An additional advantage of microcode in MCC 172 is that a complex built-in self test (BIST) can be implemented. A microcode BIST can reconfigure memory 800 and the internal circuitry of MCC 172 to perform extensive testing of the circuitry before a device fabricated with MCC 172 is packaged or shipped. This represents a significant production cost savings. Further, the MCC 172 is able to perform the tests without the need for an extensive on the packaged device, therefore bad devices are selected at wafer sort and final packaged devices will have higher yield thus reducing final device cost. Finally, the BIST microcode does not require additional circuitry nor does it require storage space in the microcode store 710 since it can be replaced with operational microcode programming after the BIST has been performed.
Initialization of microcode execution in the MCC 172 can also be accomplished in a variety of ways which are generally understood in the conventional art.
One way to initiate execution is through memory mapped function wherein a predetermined address, present upon an address bus from the core processor and corresponding to a specific function, is decoded within the MCC 172 to initiate execution of the microcode for the specific function.
The importance of memory mapped function is that MCC operations can be implemented transparently to a core processor having a memory mapped software architecture. No change is necessary to the instructions of the core processor. Integration of the MCC can be as simple as modifying I/O software drivers for each functions in the core processor software to access the addresses corresponding to the function in the MCC. Instead of process flow continuing in the core processor when a memory mapped MCC function is addressed, MCC 172 decodes the address and begins process execution.
Another alternative for initiating execution in MCC 172 includes the use of a memory location or mailbox in memory 800 which is reserved for a status word which is accessed by both the core processor and the MCC 172 in order to communicate processing state information. This approach can be implemented in the configuration illustrated in FIG. 23B. For instance, the MCC 172 will write a predetermined status word to the reserved location to indicate to the core processor that processing is complete before the MCC 172 swaps memory blocks, such as memory blocks A (150) and B (160) in
Alternatively, writing the status word to the reserved location or mailbox can also be designed to generate an interrupt to the core processor which reads the status word to determine the appropriate interrupt handling routine corresponding to the information in the status word. Implementing an interrupt driven interface between the MCC and the core processor can be useful to integrating the MCC into a memory mapped software architecture in the core processor.
The mailbox or status word architecture can also be used to create communications links between multiple MCC based devices. When one MCC device, a DSP engine for example, completes processing of a block of data, it can write to a status word to a mailbox corresponding to another MCC based device, a high speed data I/O device or FFT engine for example. Writing to the mailbox can generate an interrupt in the other MCC which reads the status word from the mailbox and initiate a function appropriate to the information in the status word. In this manner, considerable intelligence can be distributed in MCC based devices within a system and the interfaces between the MCC based subsystems can be optimized to take advantage of the high throughput capacity of the present architecture without the requirement of core processor resources.
Yet another alternative for execution initialization is to include a command register within the MCC 172, and accessible by the core processor, which receives macro-instructions from the core processor which indicate the DSP functions (or other complex operations) to be performed by the MCC 172 as well as a DMA-I/O function to be performed, along with the corresponding data addresses for each function. For DMA transfers, the macro-instruction command identifies the direction of data movement and includes such parameters as the starting and ending addresses of a block of data in memory 800 to be transferred. The macro-instructions for DSP functions and DMA transfers can be supported by underlying microcode which executes the function indicated by the macro-instruction. Still other alternatives for initiating execution in the MCC 172 include standard handshaking or interrupt driven protocols wherein various microcode programs in microcode store 710 MCC 172 constitute interrupt routines for the MCC or routines selected based upon information passed during handshaking.
The exact details of the operation of MCC 172 will vary with the particular implementation of the MCC and the microcode program. However, a general description of execution in MCC 172 follows which will demonstrate the basic principles of operation within the present architecture in the context of embodiments illustrated in
In operation, sequence controller 700 outputs a microcode address 702 to microcode store 710 in order to output a microcode control word which contains control words that direct the operation of other individual functional units within MCC 172.
The microcode control word 712 includes control word 712A which combines with output control signal 752A from execution address generator 750, to drive opcode generator 720 to generate opcodes which are output on opcode bus 178 to execution unit 130. The opcodes drive execution unit 130 to process a block of execution data originating in memory 800. In the event that multiple execution units are utilized, control word 712A and opcode generator 750 can be reconfigured to support opcode generation for the additional execution units.
In addition to controlling the algorithmic functions (adds, multiplies, etc.) of execution unit 130, the opcodes output on opcode bus 178 have the ability to reconfigure the data path of execution unit 130 under microcode control. For instance, execution unit 130 may be reconfigured from a 32 bit engine to a 16 bit engine for processing smaller operands or the execution unit could be configured to perform a four-cycle butterfly FFT for one DSP algorithm and reconfigured to perform a three-cycle butterfly FFT for a different DSP algorithm. Also, the pipeline of execution unit 130 can be reconfigured from, for example, a four deep pipeline for 32 bit operation to a two deep pipeline for 16 bit operation. Furthermore, the opcodes output on opcode bus 178 control the use of register files in execution unit 130 in order to support local storage within the execution unit.
The combined ability to control register file storage and pipeline operation in execution unit 130 results in the flexibility to achieve a wide variety of execution configurations, such as those shown in
The flexibility in execution configuration of the present invention permits a wide variety of arithmetic functions to be performed efficiently. In addition, the execution unit can be reconfigured for special non-arithmetic data paths which are useful to performing other forms of coding, such as data coding and decoding or compression and decompression.
At various points in the performance of an algorithm by execution unit 130, immediate data in the form of constants or coefficients may be needed for further processing. Control word 712B combines with control output 752B from execution address generator 750 and control output 772A from DMA address generator 770 to drive coefficient generator 730 to generate the processing constants and coefficients 732 that are required by some of the operations performed by execution unit 130. Control output 752B is included in the determination of coefficient output 732 because some algorithms require different coefficients at various points during execution of the algorithm. Control output 772A is included because coefficient requirements can change in anticipation of a swap of execution memory and DMA-I/O memory. Coefficient generator 730 can be a coefficient table or can function algorithmically to produce immediate data for execution unit 130.
Control words 712C and 712E control execution address generator 750 and DMA address generator 770 respectively. Execution address generator 750 is similar to conventional address generators that are available to support address computation for a variety of functions. Execution address generator 750 can be an address generator which produces a single address signal or can be a device with the capability to output multiple addresses, i.e. multiple addresses for access to different rows in separate memory blocks. For instance, programmable address generators are presently available which are capable of supporting the address generation patterns for FIR, FFT and convolution algorithms for digital signal processing. Other programmable address generators are available which are suitable for performing the address sequencing associated with compression and decompression algorithms. Still other programmable address generators can be used which are suitable for the specialized address generation required for other types of algorithms, such as JPEG, MPEG-2 encoder, DVD or speech recognition algorithms.
In response to control word 712C, execution address generator 750 generates execution addresses which are output on execution address bus 752 and which are latched into address register 760 which is connected to memory 800 by address bus 162. The execution addresses output to memory 800 on address bus 162 access a block of execution data which are output on data bus 184 as operands to execution unit 130. Execution address generator 750 also generates the execution addresses which are used to write the result data from execution unit 130 back into memory 800. Portions of execution address bus 752 also function as control signals to other functional units within MCC 172. Portion 752A provides input to opcode generator 720, portion 752B provides input to coefficient generator 730, portion 752C is input to latch timing and control circuit 740, portion 752D is fed back to sequence controller 700 to determine the next microcode execution address, and portion 752E is output to configuration controller 790 in order to provide input to the configuration of memory 800.
DMA address generator 770 is also similar to conventional programmable address generators and may include the capability to reorder data to allow the data to be processed more efficiently. For instance, if memory 800 is a DRAM device, then DMA address generator 770 can be instructed via control word 712E to reorder incoming data in memory 800 so that operands for execution unit 130 are located on the same data row line so that multiple accesses by execution address generator 750 to different rows of memory 800 are not necessary.
DRAM devices are typically constructed such that a single row address is common to several column addresses. When consecutive memory accesses involve data words having different row addresses then multiple address decode cycles must be performed to obtain the data words. If, however, the memory access pattern for an algorithm can be predicted, then the data can often be reordered in memory so that data words that will be accessed simultaneously or consecutively share the same memory row address. DMA address generator 770 can be instructed to perform this reordering as data is streamed into memory 800 in order to optimize later accesses to the data.
Similarly, DMA address generator 770 can be programmed to perform addressing algorithms, such as modulo, indexed or offset addressing, to reorder data in memory 800 prior to execution or after execution. Alternatively, DMA address generator 770 can be configured to operate under the direct control of a core processor, through an external bus interface mechanism such as bus interface 142 in
In response to control word 712E, DMA address generator 770 generates DMA addresses which are output on DMA address bus 772 and which are latched into address register 780 which is connected to memory 800 by address bus 782. The DMA address generation is performed in order to stream blocks of input data, i.e. data to be processed, and output data, i.e. result data, in and out of memory 800 via data bus 180. Portions of DMA address bus 772 also function as control signals to other functional units within MCC 172. Portion 772A influences coefficient generator 730, portion 772B is fed back to sequence controller 700, along with other feedback controls, to determine the next microcode execution address 702, and portion 752C is output to configuration controller 790 in order to affect the configuration of memory 800.
Multiple address generators can be utilized to support the particular requirements of a specific application. For example, in the embodiment illustrated in
Latch timing and control circuit 740 receives an opcode control signal 178A, which is part of the opcode bus 178 output from opcode generator 720, and output control signal 752C, which is part of the execution address bus 752 output from execution address generator 750, in order to generate latch timing and control signal 174. Latch timing and control signal 174 synchronizes the operation of execution unit 130 with the transfer of data with memory 800 on data bus 184 by generating the timing and control for the circuitry at the interface between execution unit 130 and memory 800 which is discussed in greater detail below. In effect, latch timing and control signal 174 coordinates the transfer of operands from memory 800 into execution unit 130 with the output of address signal 162 to memory 800. Similarly, transfer of result data from execution unit 130 is coordinated with output of execution addresses on execution address bus 162 to memory 800, in order to store the results of the processing performed by execution unit 130, by latch timing and control signal 174.
Configuration control circuit 790 receives control word 712F, along with output signal 752E from execution address generator 750 and output signal 772C from DMA address generator 770, and generates memory configuration control signal 152, which controls the sizing, partitioning and swapping of memory blocks within memory 800, such as that described earlier with regard to
Once execution of a microcode program in microcode store 710 has commenced, sequence controller 700 receives control word 712D from the microcode store 710, along with output control signal 752D from execution address generator 750, output control signal 772B from DMA address generator 770, and execution status signal 704 from execution unit 130, which represent state information, and determines the next microcode execution address to output on microcode address bus 702 in the sequence of the microcode program in microcode store 710.
In addition to multiple DMA and execution address generators and multiple execution units, there can be multiple opcode generator (720) and configuration control (790) blocks and multiple pipe-line control and latch timing and control (740) blocks. Furthermore, other known techniques for optimizing the performance of MCC 172 can be applied, such as two level microcode structuring.
Also, the execution units utilized within the architecture can be specialized units for particular functions, such as MPEG-2 encoder/decoder, graphics, data compression/decompression or other applications for which specialized execution units have been developed. Other execution units which are not specifically directed at data computation but which can directly implement compression/decompression or code/decode algorithms can be employed. One specific example is an execution unit directed at switching applications which controls decoding of the header information in data packets, stores the packets for retransmission toward their appropriate destination, and controls routing of the packets.
Dram Bandwidth Matching at Memory/Execution Unit Interface
An example of a performance enhancement achievable with the highly flexible architecture of MCC 172 of the present invention is a high speed memory interface between memory block 800 and execution unit 130. Memory access times for DRAM technology are typically on the order of 20 to 80 ns., but can vary widely depending upon such factors as the fabrication process used to produce the DRAM or the column size of the DRAM array (e.g. the number of transistors coupled to the column lines). Execution unit execution stages, on the contrary, typically cycle on the order of 2 to 6.66 ns. Memory access, therefore, can represent a severe performance bottleneck.
The latch timing and control along with the memory configuration control of the present invention, however, are capable of providing a high speed interface between memory 800 and execution unit 130 wherein multiple words are read from or written to memory in order to match the relatively slow access time of the memory 800 to the fast execution speed of execution unit 130. The high speed interface permits several words of memory 800 to be accessed in a single read or write operation so that the performance of execution unit 130 is not limited by the memory access time for memory 800.
Execution unit 130 is a pipelined execution unit operating with a cycle time of 6.66 ns., for this example, and which includes multiport local register files for feedback within the execution unit. A non-pipelined execution unit could also be utilized.
In order to interface the relatively slow memory access time to the fast execution time of the execution unit, a multi-word latch 820 is included which is sized under control of latch timing and control signal 174B from latch timing and control block 740 to compensate for the difference in memory access time and execution cycle time. For this example, multi-word latch 820 is configured for six words IW1-IW6 which are read into latch 820 in parallel, as shown in FIG. 28. When configured for a three stage execution pipeline, execution unit 130 generates a result in 20 ns. (3 stages×6.66 ns/stage). The three stage pipeline structure of execution unit 130 is shown in
Because the data in memory block A 160 is not all in the same row, under the assumption for this example that the data was not reordered when streamed into memory block A, selection logic 810 is needed to route the words read from memory into the appropriate position in multi-word latch 820. The selection logic 810 is controlled by latch timing and control signal 174A which is generated by latch timing and control circuit 740. The input words IW1-IW6 are obtained from memory blocks MM1-N and integrated by selection logic 810 for input to multi-word input latch 820. Thus, for example, data words IW1 and IW2 may be obtained from memory block MM1, words 1W3-5 from memory block MM2 and word IW6 from memory block MMN. Address signals 162A, 162B and 162C, shown in
Selection logic 810, under control of latch timing and control signal 174A, determines which sense amps in memory 800 to activate in order to route the words of data in memory 800 to the appropriate position in multi-word latch 820. As illustrated in
Multiplexor logic 830, under control of latch timing and control signal 174C, then selects and routes the data words in each of the word positions IW1-IW6 in multi-word latch 820 as operands into execution unit 130. Note that latch timing and control input 174C can reconfigure the size of the words in multi-word latch 820 to be 8, 16, 32 or more bits per word in response to opcode control signal 178A.
Corresponding reconfiguration is simultaneously implemented in the memory blocks MM1-N, selection logic 810, multiplexor logic 830, execution unit 130, high speed latch 840, DMUX logic 850, multi-word output latch 860 and selection logic 870. In addition, MUX 830 can access the words IW1-6 in any order. Therefore, two levels of switching are achieved. First, selection logic 810 performs space switching by obtaining data from anywhere within memory blocks MM1-N. Secondly, MUX 830 performs time division switching by inputting input words IW1-6 in any order desired.
Execution unit 130 performs its computations on the operands provided by multiplexor logic 830 and outputs a result which is latched into high speed latch 840. The result is then routed by DMUX logic 850 into the appropriate position of multi-word output latch 860 (OW1-OW5) for write back to appropriate address in memory block MM1-MMN, wherein output selection logic 870 selects the memory destination of each output word under control of latch control signal 174H, or back into selection logic 810 in order to provide feedback.
Each stage 130A-C of execution unit 130 is running at a clock of 6.66 ns. (20 ns. divided by 3). IW1 and IW2, for example, are multiplexed and clocked into 130A at the beginning of a first 6.66 ns. period. Then, the result from execution in 130A during the first period is clocked into 130B in the following 6.66 ns. period and the result from 130B during the second period is clocked into 130C at the beginning of a third period such that the result of the operation on IW1 and IW2 (IW1×IW2) is stored in position OW1 of output latch 860 after a three pipe stage delay of 20 ns. Subsequently, the product of IW1×1W2 is fed back and multiplied by IW3 in 130A, with the next result being stored in position OW2 of output latch 860 after 34 ns. The operand operations can be summarized as follows:
After 80 ns., the input latch 820 is free to be reloaded with another set of operands from memory blocks MM1-N because memory word IW6 has entered the pipeline. Similarly, after an initial delay due to results percolating through the execution pipeline, output latch 860 will fill every 80 ns. and be ready for a write back to memory 800 to occur. Once the pipeline is full, during each 80 ns. cycle, six words of data are read from memory 800 and input into input latch 820, 40 ns. later, for example, five words of result data in output latch 860 are written back to memory 800 and, 40 ns. after the write back, another six words are read from memory 800 and input into input latch 820. Meanwhile, operands are being continuously processed by execution unit 130 for output to output latch 860, which may require an additional temporary store positioned between DMUX 850 and output latch 860 to accommodate the results output from execution unit 130 during the 40 ns. write back cycle.
An oscillator 742 generates a 6.66 ns. period clock CLK3 which enters counter 744A and is divided into a 20 ns. clock CLK2. The 20 ns. clock signal CLK2 is then divided by counter 744B to generate an 80 ns. clock signal, CLK1. Write back of result data from multi-word output latch 860 to memory blocks MM1-N occurs at 80 ns. intervals that are staggered by 40 ns. from the read cycle and are illustrated as the dotted pulses in CLK1. The resulting clock waveforms are shown in FIG. 30A. As noted above, these clock cycle times cited are exemplary and other operating cycles may be utilized.
Latch timing and control signals 174A-H are controlled by and must be synchronized with opcode output signal 178A and execution address output signal 752C. Signals 174A-H provide both timing information and control. Signal 174A determines which data words within memory blocks MM1-N are selected by selection logic 810 and also to select them in synchronization with CLK1, in this example. Signal 174B controls the width of multi-word input latch 820 and also the latching of the data selected by selection logic 810 synchronously with CLK1, in this example. Signal 174C controls the order with which MUX 830 inputs data words IW1-IW6 into execution unit 130 in time with CLK2, in this example. Signal 174D drives the execution unit at CLK3. Signal 174E drives high speed latch 840 at CLK2 to latch results as they are output from execution unit 130. DMUX 850 is controlled by signal 174F to route the output word in high speed latch 840 to temporary storage or a word position in multi-word output latch 860 in time with CLK2. Signal 174G drives multi-word output latch 860 to receive a result word in time with CLK2 and write the result data back to memory 800 in time with CLK1. Signal 174H controls where in memory blocks MM1-N each result word OW1-6 in multi-word output latch 870 is written back in time with CLK1.
The reconfigurability of the various blocks in
One advantage to the present architecture is that most of the MCC 172 circuitry runs at the relatively slow 80 ns. clock speed of CLK1. Memory blocks MM1-N are clocked every 40 ns. by the alternating read and write cycles described above. Selection logic blocks 810 and 870 operate at the CLK1 rate. MUX 830, high speed latch 840 and DMUX logic 850 run at the 20 ns. clock speed of CLK2 (in this example, but are capable of operating at higher clock speeds). And only the pipeline stages 130A, 130B and 130C of execution unit 130 run at the highest clock speed of CLK3. Because most of the MCC 172 circuit runs at the slower clock speed, the power dissipation of the circuit is relatively low.
As discussed above, the reconfiguration of the datapath in execution unit 130 is accomplished by the opcodes 178 generated by opcode generator 720. The control signals 174A-H generated by latch timing and control block 740 are determined in part by opcode signal 178A. Therefore, the datapath can be dynamically reconfigured along with the control and timing by the output of opcode generator 720.
For instance, stages 130A and 130B can be reconfigured such that they require a slower clock cycle, for example 2×6.66 ns., in order to operate. The opcode signal 178A then combines with execution address portion 752C, as shown in
The example of
To demonstrate the flexibility available through reconfiguration of the datapath of execution unit 130, a reconfigured execution unit is shown in
As noted above, in the configuration shown in
However, DMA address generator 770 can be programmed to provide sequencing and control for aligning data for optimum processing by the execution unit 130 of algorithms which do permit reordering of the data. For instance, in DRAM memory technology, placing in the same row data which is to be accessed simultaneously (i.e. all six words, in the example, to be read into multi-word latch 820), the selection logic 810 and 870 for reading and write back, respectively, can be eliminated and memory blocks MM1-N consolidated into a single memory block to simplify the circuit and improve the effective access time of the memory to execution unit interface.
In addition, DMA address generator 770 can be programmed to reorder data after processing by execution unit 130, i.e. reorder the data while streaming the data out of memory 800. As a simple example, bytes of result data in memory 800 can be “swapped”, the higher order and lower order bytes interchanged to match another processor's data format, as the bytes of data are streamed out of memory 800 to the core processor or other destination. More sophisticated and complex reordering is also possible.
An example of the reordering discussed above is the reordering required to perform an FFT algorithm. The following is an example of a 16-point radix-2 DIT FFT implemented in MCC 172 in the configuration illustrated in FIG. 23A. First, execution is initiated, by means of one of the mechanisms for execution initiation in MCC 172 described above, which causes sequencer 700 to output, on microcode sequence signal 702, the address in microcode store 710 of a 16-point radix-2 DIT FFT microcode program. When sequencer controller 700 issues this first micro-code address for the FFT routine in micro-code store 710, micro-code store outputs a full micro-code word 712.
Microcode control word 712D is received by sequence controller 700 to set up for execution of the next microcode command in the FFT sequence, while microcode control word 712F is received by configuration control block 790 in order to determine the memory configuration control signal 152 which is output to memory block 800 to configure the memory for the FFT. In the present example, the data to be processed by execution unit 130 will be initially be loaded into memory block B 160 and will be prescrambled prior to switching memory block B 160 with memory block A 150.
Micro-code control word 712E entering DMA address generator 770, provides the following information to DMA ADDR Generator 770:
The DMA address generator 770 then reorders the data as follows:
BEFORE SCRAMBLE AFTER SCRAMBLE Location Data Location Data X (0) X (0) X + 1 (1) X + 1 (8) X + 2 (2) X + 2 (4) X + 3 (3) X + 3 (12) X + 4 (4) X + 4 (2) X + 5 (5) X + 5 (10) X + 6 (6) X + 6 (6) X + 7 (7) X + 7 (14) X + 8 (8) X + 8 (1) X + 9 (9) X + 9 (9) X + 10 (10) X + 10 (5) X + 12 (12) X + 12 (3) X + 13 (13) X + 13 (11) X + 14 (14) X + 14 (7) X + 15 (15) X + 15 (15)
The numbers in parentheses represent the offset location from X where the data was originally located.
These scrambling operations by the DMA address generator 770 involve reading X+8 (8) and storing in a temporary buffer or location and then writing X+1 (1) into X+8, this is followed by writing temporary location (TR) data (8) into location (X+1). The next step is storing X+4 (4) into the temporary buffer via read/write cycle followed by reading data located in X+2 (2) and writing into (X+4) 2. This operation is followed by reading TR data (4) and writing it into location X+2. This process continues under control of the DMA address generator 770 until all 16 points of data have been reordered. Alternatively, the microcode program in microcode store 710 can be suitably structured to program the DMA address generator 770 to reorder the data in the manner shown above as the data is streamed in from an external source, such as through Data I/O port 180.
When MCC 172 includes the hardware shown in the embodiment of
Built-In Self Test and the Memory Centric Controller 172
Another advantage to the present architecture is that an extensive BIST can be performed on the memory array 800, execution unit 130, and MCC 172 itself. The ability of MCC 172 to reconfigure the data path and timing, via opcode generator 720 and latch timing and control block 740, of execution unit 130 allows a worst case data path, or a variety of different data path configurations, to be selected for testing. In addition, latch timing and control block 740 can be configured to test execution unit 130 at an elevated clock rate. Instead of driving execution unit 130 at 6.66 ns., for example, the opcode signal 178A can be configured to operate execution unit 130 at 5 ns. timing under control of a microcode BIST loaded into microcode store 710. The elevated test clock rate enables the BIST to compensate for the differences between room temperature wafer testing of devices and higher temperature packaged testing devices. The microcode BIST is able, due to reconfiguration to a higher clock speed, to detect defective devices that will fail a BIST executed at normal clock speeds after the devices are packaged.
There is a special BIST microcode downloaded which is performed in order to do the self-test. The downloaded BIST microcode supports the selection of a worst case path in execution unit 130 through the microcode control word 712A output to opcode generator 720. For instance, instead of configuring the execution unit elements to be three or four stages deep, opcode signal 178 configures execution unit 130 to have two data paths which are two stages deep which each operate at 5 ns. in order to obtain a stress performance of the execution unit elements. The worst case path is run it at a faster clock rate during wafer testing than is the clock rate that is normally utilized during the high temperature packaged testing.
Another advantage of BIST in the present architecture is that the BIST microcoded can be downloaded from test probes at a low speed but the BIST microcode executes at high speed. Similarly, the test results and can be subsequently transferred through the test probes at a low transfer rate. Testing of an MCC based device is therefore not restricted by the electrical limitations (i.e. inductance, capacitance, noise interference, etc.) of the test probe interface to the MCC based device.
Also, using the test microcode, the entire memory block 800 can be minutely checked because the test microcode controls configuration control block 790 in order to perform a variety of memory configuration set-ups to check the function of the sense amps within memory array 800. Memory array 800 can be configured to have multiple memory blocks, such as block 150 and 160, which can be checked by switching the blocks back and forth. Also, memory test patterns, such as a checkerboard pattern, can be written into memory and read back out in order to check the function of individual memory cells in memory array 800. Defective memory elements can be located and information relating to the location of defective cells can be output so that a determination can be made of what circuitry to burn in through a laser fuse in order to replace the defective cells with redundant memory elements which are typically included when memory arrays are fabricated.
The defective memory element information can be output as a status word or other data which can be output through a dedicated test port or through a status word in memory array 800 which is accessible through the data interface ports, such as data I/O bus 180 or external bus interface mechanism 142, which are already provided by the present architecture. Compilation and output of status information is performed, again, under control of the microcode self test. The result is a high powered memory based device which can test itself and which can reconfigure itself to obtain worst case or special case testing.
Power Management by MCC 172
The MCC 172 also has the capability to manage the power dissipation of execution unit 130 and the components of MCC 172. As was described above with respect to latch timing and control block 740 and
Thus, because the microcode program for the algorithm in microcode store 710 has embedded in it the control information to modify the speed of data transfer through input latch 820, MUX 830, high speed latch 840, DMUX 850, execution unit 130 and output latch 860, the microcode also has the capability of controlling the power dissipation of these circuits by reconfiguring the clock cycle times of the circuits. For instance, as described in the example above, MUX 830, under the control of latch timing and control signal 174C, selects an operand from input latch 820 for input to the pipeline of execution unit 130 at the 20 ns. intervals of CLK2. In fact, operands can be selected at the 6.66 ns. clock rate of CLK3 constituting a threefold increase in the operating frequency, and therefore the power dissipation, of MUX 830. Thus, by moving data from latch 820 into execution unit 130 at 20 ns. intervals, a substantial improvement in power dissipation is achieved.
In addition, the microcode program can include multiple subroutines which support different levels of performance of an algorithm and, consequently, also support different levels of power dissipation. The microcode program can be structured to select a microcode subroutine which configures execution address generator 750, opcode generator 720 and latch timing and control circuit 740 for slower operation when fast performance is not required. Power dissipation is reduced in the execution address generator 750, the opcode generator 720 and latch timing and control 740 by the microcode selected for an algorithm. The opcode generator block 720 and latch timing and control block 740 have their power reduced by microcode that generates slower signal frequencies in latch timing and control signals 174A-H to the data path and reducing the requirements of the opcode output 178 (updates of the execution unit and latches occur less frequently which decreases the operating frequency). This also means less power is dissipated in the latch timing and control unit 740 itself. Thus, there is power reduction achieved within the three major block levels described above. Also note that the reconfiguration of the data path will also result in reduction of power dissipation. The important consideration here is that the microcode subroutine can effect the power dissipation of algorithmic calculations by determining the timing rates for latches and timing signals for pipe-lines in the execution unit, and indeed, the nature of the reconfiguration of the execution units themselves.
The above power reduction technique, in addition to being enabled through a specific piece of micro-code, can also be enabled via branching into a segment of microcode that enables less power dissipation. For example, for a given algorithm there may be more than one micro-code subroutine which would support the algorithm of different levels of power dissipation and speed. Thus, through a branching option, this selection would be determined. For example, when more then one algorithm is being processed concurrently through the execution unit 130, it may be necessary to utilize the faster speeds in the latch timing and control signals 174A-H and faster issuance of opcodes in opcode signal 178 in order to meet the throughput requirements of the algorithm. However, when only one algorithm is being processed in execution unit 130, slower latch timing and control and issuance of opcodes can be accommodated. An example would be executing an FIR and FFT through parallel data paths in execution unit 130 with the goal of providing maximum throughput versus executing an FIR alone in which the highest throughput was not necessary.
The reduction of power dissipation by arranging branching, as discussed above, is not the sole reason for utilization of a branching mechanism in this architecture. There are two levels of branching in the present architecture. The first level of branching is at a slower speed and occurs through the operation of sequence controller 700 and sequences at a rate equivalent to approximately the read/write cycle time of memory array 800, which is typically a DRAM. Power dissipation in sequence controller 700 is reduced because the slower operational speed allows for minimal size device transistors, since the performance of sequence controller 700 does not have to perform at a high clock rate, and simpler levels of chips interconnect can be utilized.
As illustrated in
However, to accomplish a high-speed branch, additions need to be made to the architecture which are illustrated in FIG. 33. The execution unit 130 provides feedback control information signals 704A to opcode generator 720 and 704B to latch timing and control circuit 740. Feedback signal 704 continues to be connected to sequence controller 700. The feedback of signals 704A and 704B is necessary to enable a high-speed branch to occur within the processing performed within the execution unit 130 as opposed to the lower speed branch associated with sequence controller 700. Specifically, the high-speed branch arranges modifications to the operations which take place within the circuitry illustrated in
An example of fast branching involves executing a first FIR algorithm FIR A followed by a branch to one of a second FIR algorithm FIR B and a convolution algorithm CONV B, which is illustrated in FIG. 34. The data required for implementing FIR A, which involves a small number of data points, is loaded into multi-word input latch 820 (or a multi-ported register file which takes the place of blocks 820 and 830). After FIR A completes, a fast branch occurs to either FIR B or CONV B depending on a branch condition resulting from FIR A which feeds back to opcode generator 720 via feedback signal 704A and latch timing and control block 740 via feedback signal 704B, as shown in FIG. 33.
Note that the high speed branch to either FIR B or CONV B is achieved by opcode generator 720 and latch timing and control block 740 in response to the feedback signals 704A and 704B. Opcode generator 720 issues the next opcode on opcode output signal 178 and outputs opcode control signal 178A to latch timing and control block 740 to drive the next latch timing and control signals 174A-H in order to execute either FIR B or CONV B, depending upon the branch feedback condition reflected in feedback signals 704A and 704B.
Speculative Execution in MCC 172
The present architecture also has the capability to perform speculative execution. Expanding upon the example discussed above in regard to
For instance, execution unit 130 can be configured, as described above, to have two parallel data paths wherein FIR A and FIR B are calculated in the first data path and CONV B is calculated in the second data path. Note that since these operations require multiple accesses to memory 800, execution address generator 750 (or multiple address generators) provides address generation for the processes of all three algorithms running in parallel. This can be accomplished by a high level address generator capable of generating addresses for multiple processes (algorithmic memory addressing) being addressed concurrently or by the use of smaller address generators where each smaller address generator handles one process. The result of address generation is that operands are obtained from memory 800 and input to execution unit 130 for FIR A, FIR B and CONV B in parallel. The results from FIR B and CONV B are held in temporary memory locations until FIR A completes thereby setting the branch condition. Based upon the branch condition from FIR A, the temporary memory location for either FIR B or CONV B is switched into the final result segment of storage in memory 800, e.g., switched into working memory through reconfiguration of the memory. Thus, reconfiguration of memory 800 also comes into play in obtaining speculative execution in the present architecture. The process flow of the present example is illustrated in FIG. 35.
The configuration of memory 800 into working memory and temporary memory locations 1-N, as shown in
Note that it is possible, in the event that FIR A completes and the algorithm FIR B or CONV B that is selected based upon the results of FIR A has not completed execution, to reconfigure execution unit 130 to devote more processing resources to completion of the selected algorithm. At the same time, memory 800 can be reconfigured to couple the temporary memory location for the selected results into the working memory containing the results of FIR A.
Further note from the present example that reconfiguration of memory 800 together with speculative execution combine to accomplish higher execution speed for computational algorithms.
Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. I claim all modifications and variation coming within the spirit and scope of the following claims.
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|U.S. Classification||710/22, 710/65, 375/E07.094, 712/10, 375/E07.211, 712/220, 712/E09.067|
|International Classification||H04N7/26, H04N7/50, G06F9/38|
|Cooperative Classification||H04N19/423, H04N19/61, G06F9/3897, G06F9/3879, G06F2213/0038|
|European Classification||G06F9/38S1, G06F9/38T8C2, H04N7/26L2, H04N7/50|
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