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https://github.com/ipxe/ipxe
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[liba20] Rename libflat to liba20
libflat no longer has anything to do with flat real mode; it handles only the A20 gate. Update library name to match. Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
305
src/arch/i386/transitions/liba20.S
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305
src/arch/i386/transitions/liba20.S
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/*
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* Copyright (C) 2010 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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FILE_LICENCE ( GPL2_OR_LATER )
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.arch i386
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/****************************************************************************
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* test_a20_short, test_a20_long
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*
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* Check to see if A20 line is enabled
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*
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* Parameters:
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* none
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* Returns:
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* CF set if A20 line is not enabled
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* Corrupts:
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* none
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****************************************************************************
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*/
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#define TEST_A20_SHORT_MAX_RETRIES 0x20
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#define TEST_A20_LONG_MAX_RETRIES 0x200000
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.section ".text16.early", "awx", @progbits
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.code16
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test_a20_short:
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pushl %ecx
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movl $TEST_A20_SHORT_MAX_RETRIES, %ecx
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jmp 1f
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.size test_a20_short, . - test_a20_short
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test_a20_long:
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pushl %ecx
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movl $TEST_A20_LONG_MAX_RETRIES, %ecx
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1: pushw %ax
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pushw %ds
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pushw %es
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/* Set up segment registers for access across the 1MB boundary */
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xorw %ax, %ax
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movw %ax, %ds
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decw %ax
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movw %ax, %es
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2: /* Modify and check test pattern; succeed if we see a difference */
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pushfw
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cli
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xchgw %ds:0, %cx
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movw %es:0x10, %ax
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xchgw %ds:0, %cx
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popfw
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cmpw %ax, %cx
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clc
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jnz 99f
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/* Delay and retry */
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outb %al, $0x80
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addr32 loop 2b
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stc
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99: /* Restore registers and return */
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popw %es
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popw %ds
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popw %ax
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popl %ecx
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ret
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.size test_a20_long, . - test_a20_long
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/****************************************************************************
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* enable_a20_bios
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*
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* Try enabling A20 line via BIOS
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*
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* Parameters:
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* none
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* Returns:
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* CF set if A20 line is not enabled
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* Corrupts:
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* none
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****************************************************************************
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*/
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.section ".text16.early", "awx", @progbits
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.code16
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enable_a20_bios:
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/* Preserve registers */
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pushw %ax
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/* Attempt INT 15,2401 */
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movw $0x2401, %ax
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int $0x15
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jc 99f
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/* Check that success was really successful */
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call test_a20_short
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99: /* Restore registers and return */
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popw %ax
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ret
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.size enable_a20_bios, . - enable_a20_bios
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/****************************************************************************
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* enable_a20_kbc
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*
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* Try enabling A20 line via keyboard controller
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*
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* Parameters:
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* none
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* Returns:
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* CF set if A20 line is not enabled
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* Corrupts:
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* none
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****************************************************************************
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*/
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#define KC_RDWR 0x60
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#define KC_RDWR_SET_A20 0xdf
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#define KC_CMD 0x64
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#define KC_CMD_WOUT 0xd1
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#define KC_CMD_NULL 0xff
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#define KC_STATUS 0x64
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#define KC_STATUS_OBUF_FULL 0x01
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#define KC_STATUS_IBUF_FULL 0x02
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#define KC_MAX_RETRIES 100000
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.section ".text16.early", "awx", @progbits
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.code16
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enable_a20_kbc:
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/* Preserve registers */
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pushw %ax
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/* Try keyboard controller */
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call empty_kbc
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movb $KC_CMD_WOUT, %al
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outb %al, $KC_CMD
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call empty_kbc
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movb $KC_RDWR_SET_A20, %al
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outb %al, $KC_RDWR
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call empty_kbc
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movb $KC_CMD_NULL, %al
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outb %al, $KC_CMD
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call empty_kbc
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/* Check to see if it worked */
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call test_a20_long
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/* Restore registers and return */
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popw %ax
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ret
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.size enable_a20_kbc, . - enable_a20_kbc
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.section ".text16.early", "awx", @progbits
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.code16
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empty_kbc:
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/* Preserve registers */
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pushl %ecx
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pushw %ax
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/* Wait for KBC to become empty */
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movl $KC_MAX_RETRIES, %ecx
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1: outb %al, $0x80
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inb $KC_STATUS, %al
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testb $( KC_STATUS_OBUF_FULL | KC_STATUS_IBUF_FULL ), %al
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jz 99f
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testb $KC_STATUS_OBUF_FULL, %al
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jz 2f
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outb %al, $0x80
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inb $KC_RDWR, %al
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2: addr32 loop 1b
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99: /* Restore registers and return */
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popw %ax
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popl %ecx
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ret
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.size empty_kbc, . - empty_kbc
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/****************************************************************************
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* enable_a20_fast
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*
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* Try enabling A20 line via "Fast Gate A20"
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*
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* Parameters:
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* none
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* Returns:
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* CF set if A20 line is not enabled
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* Corrupts:
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* none
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****************************************************************************
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*/
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#define SCP_A 0x92
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.section ".text16.early", "awx", @progbits
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.code16
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enable_a20_fast:
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/* Preserve registers */
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pushw %ax
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/* Try "Fast Gate A20" */
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inb $SCP_A, %al
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orb $0x02, %al
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andb $~0x01, %al
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outb %al, $SCP_A
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/* Check to see if it worked */
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call test_a20_long
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/* Restore registers and return */
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popw %ax
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ret
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.size enable_a20_fast, . - enable_a20_fast
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/****************************************************************************
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* enable_a20
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*
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* Try enabling A20 line via any available method
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*
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* Parameters:
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* none
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* Returns:
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* CF set if A20 line is not enabled
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* Corrupts:
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* none
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****************************************************************************
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*/
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#define ENABLE_A20_RETRIES 255
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.section ".text16.early", "awx", @progbits
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.code16
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.globl enable_a20
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enable_a20:
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/* Preserve registers */
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pushl %ecx
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pushw %ax
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/* Check to see if A20 is already enabled */
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call test_a20_short
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jnc 99f
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/* Use known working method, if we have one */
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movw %cs:enable_a20_method, %ax
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testw %ax, %ax
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jz 1f
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call *%ax
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jmp 99f
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1:
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/* Try all methods in turn until one works */
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movl $ENABLE_A20_RETRIES, %ecx
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2: movw $enable_a20_bios, %ax
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movw %ax, %cs:enable_a20_method
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call *%ax
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jnc 99f
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movw $enable_a20_kbc, %ax
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movw %ax, %cs:enable_a20_method
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call *%ax
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jnc 99f
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movw $enable_a20_fast, %ax
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movw %ax, %cs:enable_a20_method
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call *%ax
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jnc 99f
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addr32 loop 2b
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/* Failure; exit with carry set */
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movw $0, %cs:enable_a20_method
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stc
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99: /* Restore registers and return */
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popw %ax
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popl %ecx
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ret
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.section ".text16.early.data", "aw", @progbits
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.align 2
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enable_a20_method:
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.word 0
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.size enable_a20_method, . - enable_a20_method
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/****************************************************************************
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* access_highmem (real mode far call)
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*
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* Open up access to high memory with A20 enabled
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*
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* Parameters:
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* none
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* Returns:
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* CF set if high memory could not be accessed
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* Corrupts:
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* none
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****************************************************************************
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*/
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.section ".text16.early", "awx", @progbits
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.code16
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.globl access_highmem
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access_highmem:
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/* Enable A20 line */
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call enable_a20
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lret
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.size access_highmem, . - access_highmem
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