sys/arch/i386/stand/lib/gatea20.c
/*	$NetBSD: gatea20.c,v 1.12 2009/08/23 12:31:05 jmcneill Exp $	*/

/* extracted from freebsd:sys/i386/boot/biosboot/io.c */

#include <sys/types.h>

#include <lib/libsa/stand.h>

#include "libi386.h"
#include "biosmca.h"
#include "cpufunc.h"

#define K_RDWR 		0x60		/* keyboard data & cmds (read/write) */
#define K_STATUS 	0x64		/* keyboard status */
#define K_CMD	 	0x64		/* keybd ctlr command (write-only) */

#define K_OBUF_FUL 	0x01		/* output buffer full */
#define K_IBUF_FUL 	0x02		/* input buffer full */

#define KC_CMD_WIN	0xd0		/* read  output port */
#define KC_CMD_WOUT	0xd1		/* write output port */
#define KB_A20		0x9f		/* enable A20,
					   reset (!),
					   enable output buffer full interrupt
					   enable data line
					   disable clock line */

/*
 * Gate A20 for high memory
 */
static unsigned char	x_20 = KB_A20;

void
gateA20(void)
{
	int biosA20(void);
	u_long psl;

	/*
	 * First, try asking the BIOS to enable A20.
	 *
	 * If that fails, try system configuration port 0x92 but only
	 * if known to be necessary.  Not all systems enable A20 via the
	 * keyboard controller, some don't have keyboard controllers,
	 * and playing with port 0x92 may cause some systems to break.
	 *
	 * Otherwise, use the traditional method (keyboard controller).
	 */
	if (!biosA20())
		return;
	psl = x86_read_psl();
	x86_disable_intr();
	if (
#ifdef SUPPORT_PS2
	    biosmca_ps2model == 0xf82 ||
#endif
	    (inb(K_STATUS) == 0xff && inb(K_RDWR) == 0xff)) {
		int data;

		data = inb(0x92);
		outb(0x92, data | 0x2);
	} else {
		while (inb(K_STATUS) & K_IBUF_FUL);

		while (inb(K_STATUS) & K_OBUF_FUL)
			(void)inb(K_RDWR);

		outb(K_CMD, KC_CMD_WOUT);

		while (inb(K_STATUS) & K_IBUF_FUL);

		outb(K_RDWR, x_20);

		while (inb(K_STATUS) & K_IBUF_FUL);

		while (inb(K_STATUS) & K_OBUF_FUL)
			(void)inb(K_RDWR);
	}
	x86_write_psl(psl);
}
