/*
* Copyright (C) 2010 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )
.section ".note.GNU-stack", "", @progbits
.code16
.arch i386
/****************************************************************************
* test_a20_short, test_a20_long
*
* Check to see if A20 line is enabled
*
* Parameters:
* none
* Returns:
* CF set if A20 line is not enabled
* Corrupts:
* none
****************************************************************************
*/
#define TEST_A20_SHORT_MAX_RETRIES 0x20
#define TEST_A20_LONG_MAX_RETRIES 0x200000
.section ".text16.early", "awx", @progbits
.code16
test_a20_short:
pushl %ecx
movl $TEST_A20_SHORT_MAX_RETRIES, %ecx
jmp 1f
.size test_a20_short, . - test_a20_short
test_a20_long:
pushl %ecx
movl $TEST_A20_LONG_MAX_RETRIES, %ecx
1: pushw %ax
pushw %ds
pushw %es
/* Set up segment registers for access across the 1MB boundary */
xorw %ax, %ax
movw %ax, %ds
decw %ax
movw %ax, %es
2: /* Modify and check test pattern; succeed if we see a difference */
pushfw
cli
xchgw %ds:0, %cx
movw %es:0x10, %ax
xchgw %ds:0, %cx
popfw
cmpw %ax, %cx
clc
jnz 99f
/* Delay and retry */
outb %al, $0x80
addr32 loop 2b
stc
99: /* Restore registers and return */
popw %es
popw %ds
popw %ax
popl %ecx
ret
.size test_a20_long, . - test_a20_long
/****************************************************************************
* enable_a20_bios
*
* Try enabling A20 line via BIOS
*
* Parameters:
* none
* Returns:
* CF set if A20 line is not enabled
* Corrupts:
* none
****************************************************************************
*/
.section ".text16.early", "awx", @progbits
.code16
enable_a20_bios:
/* Preserve registers. Be very paranoid, since some BIOSes
* are reported to clobber %ebx
*/
pushal
/* Attempt INT 15,2401 */
movw $0x2401, %ax
int $0x15
jc 99f
/* Check that success was really successful */
call test_a20_short
99: /* Restore registers and return */
popal
ret
.size enable_a20_bios, . - enable_a20_bios
/****************************************************************************
* enable_a20_kbc
*
* Try enabling A20 line via keyboard controller
*
* Parameters:
* none
* Returns:
* CF set if A20 line is not enabled
* Corrupts:
* none
****************************************************************************
*/
#define KC_RDWR 0x60
#define KC_RDWR_SET_A20 0xdf
#define KC_CMD 0x64
#define KC_CMD_WOUT 0xd1
#define KC_CMD_NULL 0xff
#define KC_STATUS 0x64
#define KC_STATUS_OBUF_FULL 0x01
#define KC_STATUS_IBUF_FULL 0x02
#define KC_MAX_RETRIES 100000
.section ".text16.early", "awx", @progbits
.code16
enable_a20_kbc:
/* Preserve registers */
pushw %ax
/* Try keyboard controller */
call empty_kbc
movb $KC_CMD_WOUT, %al
outb %al, $KC_CMD
call empty_kbc
movb $KC_RDWR_SET_A20, %al
outb %al, $KC_RDWR
call empty_kbc
movb $KC_CMD_NULL, %al
outb %al, $KC_CMD
call empty_kbc
/* Check to see if it worked */
call test_a20_long
/* Restore registers and return */
popw %ax
ret
.size enable_a20_kbc, . - enable_a20_kbc
.section ".text16.early", "awx", @progbits
.code16
empty_kbc:
/* Preserve registers */
pushl %ecx
pushw %ax
/* Wait for KBC to become empty */
movl $KC_MAX_RETRIES, %ecx
1: outb %al, $0x80
inb $KC_STATUS, %al
testb $( KC_STATUS_OBUF_FULL | KC_STATUS_IBUF_FULL ), %al
jz 99f
testb $KC_STATUS_OBUF_FULL, %al
jz 2f
outb %al, $0x80
inb $KC_RDWR, %al
2: addr32 loop 1b
99: /* Restore registers and return */
popw %ax
popl %ecx
ret
.size empty_kbc, . - empty_kbc
/****************************************************************************
* enable_a20_fast
*
* Try enabling A20 line via "Fast Gate A20"
*
* Parameters:
* none
* Returns:
* CF set if A20 line is not enabled
* Corrupts:
* none
****************************************************************************
*/
#define SCP_A 0x92
.section ".text16.early", "awx", @progbits
.code16
enable_a20_fast:
/* Preserve registers */
pushw %ax
/* Try "Fast Gate A20" */
inb $SCP_A, %al
orb $0x02, %al
andb $~0x01, %al
outb %al, $SCP_A
/* Check to see if it worked */
call test_a20_long
/* Restore registers and return */
popw %ax
ret
.size enable_a20_fast, . - enable_a20_fast
/****************************************************************************
* enable_a20
*
* Try enabling A20 line via any available method
*
* Parameters:
* none
* Returns:
* CF set if A20 line is not enabled
* Corrupts:
* none
****************************************************************************
*/
#define ENABLE_A20_RETRIES 255
.section ".text16.early", "awx", @progbits
.code16
.globl enable_a20
enable_a20:
/* Preserve registers */
pushl %ecx
pushw %ax
/* Check to see if A20 is already enabled */
call test_a20_short
jnc 99f
/* Use known working method, if we have one */
movw %cs:enable_a20_method, %ax
testw %ax, %ax
jz 1f
call *%ax
jmp 99f
1:
/* Try all methods in turn until one works */
movl $ENABLE_A20_RETRIES, %ecx
2: movw $enable_a20_bios, %ax
movw %ax, %cs:enable_a20_method
call *%ax
jnc 99f
movw $enable_a20_kbc, %ax
movw %ax, %cs:enable_a20_method
call *%ax
jnc 99f
movw $enable_a20_fast, %ax
movw %ax, %cs:enable_a20_method
call *%ax
jnc 99f
addr32 loop 2b
/* Failure; exit with carry set */
movw $0, %cs:enable_a20_method
stc
99: /* Restore registers and return */
popw %ax
popl %ecx
ret
.section ".text16.early.data", "aw", @progbits
.balign 2
enable_a20_method:
.word 0
.size enable_a20_method, . - enable_a20_method
/****************************************************************************
* access_highmem (real mode far call)
*
* Open up access to high memory with A20 enabled
*
* Parameters:
* none
* Returns:
* CF set if high memory could not be accessed
* Corrupts:
* none
****************************************************************************
*/
.section ".text16.early", "awx", @progbits
.code16
.globl access_highmem
access_highmem:
/* Enable A20 line */
call enable_a20
lret
.size access_highmem, . - access_highmem
