/* real-mode A20 gate control code for grub4dos. * *  Copyright (C) 2008 Tinybit <tinybit@tom.com> * *  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 *  (at your option) 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., 675 Mass Ave, Cambridge, MA 02139, USA. *//* The code is based on bcopy32.c from syslinux-3.63. Here is the original * copyright notice: * * ----------------------------------------------------------------------- * *   Copyright 1994-2008 H. Peter Anvin - All Rights Reserved * *   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, Inc., 53 Temple Place Ste 330, *   Boston MA 02111-1307, USA; either version 2 of the License, or *   (at your option) any later version; incorporated herein by reference. * * ----------------------------------------------------------------------- */## Routines to enable and disable (yuck) A20.  These routines are gathered# from tips from a couple of sources, including the Linux kernel and# http://www.x86.org/.  The need for the delay to be as large as given here# is indicated by Donnie Barnes of RedHat, the problematic system being an# IBM ThinkPad 760EL.## We typically toggle A20 twice for every 64K transferred.##define	DISABLE_CPU_CACHE	1#define IO_DELAY_PORT	0x80		/* Invalid port (we hope!) */# Note the skip of 2 here#define A20_DUNNO	0		/* A20 type unknown */#define A20_NONE	2		/* A20 always on? */#define A20_BIOS	4		/* A20 BIOS enable */#define A20_KBC		6		/* A20 through KBC */#define A20_FAST	8		/* A20 through port 92h */enable_disable_a20:	###################################################################	# input:	DL=0		disable a20	#		DL=non-zero	enable a20	#		DH=0		a20 debug off	#		DH=non-zero	a20 debug on	#		CX=loops to try when failure	#	# output:	ZF=0		failed	#		ZF=1		completed ok. If ZF=CF=1, then	#				the A20 status needn't change and	#				was not touched.	#		EAX modified	#		CX modified	###################################################################	# First, see if the A20 status is already what we desired.	pushl	%ecx	movl	$0x2, %ecx	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	jnz	1f	stc	retassign_base_pointer:	call	base_addrbase_addr:	popw	%bp	ret1:	/********************************************/	/**  Now we have to enable or disable A20  **/	/********************************************/	pushal			# save all	movw	$200, %cx	testb	%dl, %dl	jnz	1f	movw	$20, %cx1:	call	assign_base_pointer	/* BP points to base_addr */	# Times to try to make this work	movw	%cx, %cs:(A20Tries - base_addr)(%bp)	/* save DX */	movw	%dx, %cs:(A20Config - base_addr)(%bp)	/* save original IF, DF */	pushfw	popw	%cs:(A20Flags - base_addr)(%bp)	/* save original return address */	movw	%sp, %bp	pushw	32(%bp)	call	assign_base_pointer	/* BP points to base_addr */	popw	%cs:(A20ReturnAddress - base_addr)(%bp)a20_try_again:	######################################################################	## If the A20 type is known, jump straight to type	######################################################################	call	assign_base_pointer	/* BP points to base_addr */	movw	%cs:(A20Type - base_addr)(%bp), %si	movw	%bp, %bx	addw	%cs:(A20List - base_addr)(%bp, %si), %bx	jmp	*%bx	######################################################################	## First, see if we are on a system with no A20 gate	######################################################################	/*	 * If the system has no A20 gate, then we needn't enable it and could	 * return SUCCESS right now without calling A20_TEST.	 */a20_none:	testb	%dl, %dl	jz	a20_done_fail//	cmpb	%dl, %dl	# set ZF=1 for success//	jmp	a20_donea20_dunno:	//movb	$A20_DUNNO, %cs:(A20Type - base_addr)(%bp)	call	a20_debug_print	pushl	%ecx	movl	$0x2, %ecx	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	jz	a20_done	#######################################################	## Next, try the BIOS (INT 15h AX=240xh)	#######################################################a20_bios:#if 0	/* dell hangs on the A20 BIOS call, so we avoid calling it. */		testb	%dl, %dl	jz	1f	call	assign_base_pointer	/* BP points to base_addr */	movb	$A20_BIOS, %cs:(A20Type - base_addr)(%bp)	call	a20_debug_print1:	pushw	%bp		/* in case it is destroyed by int 15 */	pushw	%dx		/* in case it is destroyed by int 15 */	pushfw			# Some BIOSes muck with IF	testb	%dl, %dl	setnz	%al	movb	$0x24, %ah.ifdef int13_handler.ifdef ROM_int15	/* we are inside asm.S */	pushfw	lcall	%cs:*(ROM_int15 - int13_handler).else	int	$0x15.endif.else	int	$0x15.endif	popfw	popw	%dx	popw	%bp	/* restore BP and DX in the safest way! */	call	assign_base_pointer	/* BP points to base_addr */	movw	%cs:(A20Config - base_addr)(%bp), %dx	/* restore original return address */	movw	%cs:(A20ReturnAddress - base_addr)(%bp), %ax	movw	%sp, %bp	movw	%ax, 32(%bp)		/* update the stack! */	call	assign_base_pointer	/* BP points to base_addr */	/* restore original IF, DF */	pushw	%cs:(A20Flags - base_addr)(%bp)	popfw	pushl	%ecx	movl	$0x2, %ecx	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	jz	a20_done#endif	#######################################################	## Enable the keyboard controller A20 gate	#######################################################a20_kbc:	call	empty_8042	pushfw			# ZF=0 indicates there is no 8042	pushl	%ecx	movl	$0x2, %ecx	call	a20_test_match	popl	%ecx	popw	%ax		# flags	/* ZF=1(means equal) for desired and we needn't do anything. */	jz	a20_done	# A20 live, no need to use KBC	pushw	%ax		# flags	popfw	jnz	a20_fast	# failure, no 8042, try next	testb	%dl, %dl	jz	1f	call	assign_base_pointer	/* BP points to base_addr */	movb	$A20_KBC, %cs:(A20Type - base_addr)(%bp)	call	a20_debug_print1:	movb	$0xD1, %al	# 8042 command byte to write output port	outb	%al, $0x64	# write command to port 64h	call	empty_8042	movb	$0xDD, %al	# 0xDD is for disable, 0xDF is for enable	testb	%dl, %dl	setne	%ah	shlb	$1, %ah	orb	%ah, %al	outb	%al, $0x60	call	empty_8042	pushl	%ecx	movl	$0x2, %ecx	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	pushfw			# ZF=1 for "A20 is OK"	/* output a dummy command (USB keyboard hack) */	movb	$0xFF, %al	outb	%al, $0x64	call	empty_8042	popfw			# ZF=1 for "A20 is OK"	jz	a20_done	# A20 live, no need to use KBC	pushl	%ecx	movl	$0x2, %ecx	# 0x200000 is too big	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	jz	a20_done	######################################################################	## Fast A20 Gate: System Control Port A	######################################################################a20_fast:	inb	$0x92, %al	testb	%dl, %dl	jz	2f	/* enable a20 */	call	assign_base_pointer	/* BP points to base_addr */	movb	$A20_FAST, %cs:(A20Type - base_addr)(%bp)	call	a20_debug_print	testb	$0x02, %al	jnz	1f		# chipset bug: do nothing if already set	orb	$0x02, %al	# "fast A20" version	andb	$0xFE, %al	# don't accidentally reset the cpu	jmp	3f2:	/* disable a20 */	testb	$0x02, %al	jz	1f		# chipset bug: do nothing if already cleared	andb	$0xFC, %al	# don't accidentally reset the cpu3:	outb	%al, $0x921:	pushl	%ecx	movl	$0x8, %ecx	# 0x200000 is too big	call	a20_test_match	popl	%ecx	/* ZF=1(means equal) for desired and we needn't do anything. */	jz	a20_done	#==================================================================	#	A20 is not responding.  Try again.	#==================================================================	/* A20Type is now A20_FAST, so it must be reset!! */	call	assign_base_pointer	/* BP points to base_addr */	movb	$A20_DUNNO, %cs:(A20Type - base_addr)(%bp)	call	a20_debug_print	decw	%cs:(A20Tries - base_addr)(%bp)	jnz	a20_try_again	#==================================================================	#	Finally failed.	#==================================================================	testb	%dl, %dl	jnz	a20_done_fail	/* We cannot disable it, so consider there is no A20 gate. */	call	assign_base_pointer	/* BP points to base_addr */	movb	$A20_NONE, %cs:(A20Type - base_addr)(%bp)a20_done_fail:	incw	%dx		# set ZF=0 for failurea20_done:	pushfw	/* print "done!" to show that a return was executed */	testb	%dh, %dh	jz	1f	call	assign_base_pointer	/* BP points to base_addr */	leaw	(A20DbgMsgEnd - base_addr)(%bp), %si	/* CS:SI is string */	call	a20_print_string1:	popfw	popal	ret//////////////////////////////////////////////////////////////////////////////////	///////////////////////////////////////////////////////////	////	//	Subroutines begin here//	////	/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////	######################################################################	## This routine tests if A20 status matches the desired.	######################################################################a20_test_match:1:	call	a20_test	sete	%al		/* save ZF to AL */	testb	%dl, %dl	sete	%ah		/* save ZF to AH */	cmpb	%al, %ah	ADDR32 loopnz	1b	/* dec ECX */	/* ZF=1(means equal) for match */	ret	######################################################################	## This routine tests if A20 is enabled (ZF = 0).  This routine	## must not destroy any register contents.	######################################################################a20_test:	pushl	%eax	pushw	%cx	pushw	%ds	pushw	%es	pushw	%si	pushw	%di	pushfw				/* save old IF, DF */#if DISABLE_CPU_CACHE	/* disable CPU cache for the test to work reliably. */	movl	%cr0, %eax	pushl	%eax			/* save old cr0 */	orl	$0x60000000, %eax	/* set CD and NW */	movl	%eax, %cr0	movl	%cr0, %eax	testl	$0x60000000, %eax	/* check if we can use wbinvd. */	jz	1f			/* CPU has no wbinvd instruction. */	wbinvd	andl	$0xDFFFFFFF, %eax	/* clear NW */	movl	%eax, %cr01:#endif	xorw	%ax, %ax	movw	%ax, %ds	/* DS=0 */	decw	%ax	movw	%ax, %es	/* ES=0xFFFF */	movw	$(0xFFF0 / 4), %cx	xorw	%si, %si	movw	$0x0010, %di	cld	repz cmpsl	jne	1f		/* A20 is known to be enabled */	/* A20 status unknown */	movl	0, %eax	pushl	%eax		/* save old int 0 vector */	movw	$32, %cx	# Loop count	cli			/* safe to touch int 0 vector */2:	incl	%eax	movl	%eax, 0	call	delay		# Serialize, and fix delay	cmpl	%es:0x10, %eax	loopz	2b	popl	%eax		/* restore int 0 vector */	movl	%eax, 01:	/* ZF=0(means not equal) for A20 on, ZF=1(means equal) for A20 off. */#if DISABLE_CPU_CACHE	popl	%eax		/* restore cr0 */	movl	%eax, %cr0#endif	lahf			/* Load Flags into AH Register. */				/* AH = SF:ZF:xx:AF:xx:PF:xx:CF */		popfw			/* restore IF, DF */	sahf			/* update ZF */	popw	%di	popw	%si	popw	%es	popw	%ds	popw	%cx	popl	%eax	retslow_out:	outb	%al, %dx	# Fall throughdelay:	pushw	%ax	movb	$0x80, %al	/* try to write only a known value to port */	outb	%al, $IO_DELAY_PORT	outb	%al, $IO_DELAY_PORT	popw	%ax	ret	######################################################################	##	## Print A20Tries, A20Type	##	######################################################################a20_debug_print:	testb	%dh, %dh	/* debug mode? */	jnz	1f		/* yes, continue */	ret1:	pushal	call	assign_base_pointer	/* BP points to base_addr */	movb	%cs:(A20Tries - base_addr)(%bp), %al		/* A20Tries */	call	a20_hex	movw	%ax, %cs:(A20DbgMsgTryHex - base_addr)(%bp)	/* A20Tries */	movb	%cs:(A20Type - base_addr)(%bp), %al		/* A20Type */	call	a20_hex	movw	%ax, %cs:(A20DbgMsgTryHex - base_addr + 2)(%bp)	/* A20Type */	leaw	(A20DbgMsgTry - base_addr)(%bp), %si	/* CS:SI is string */	call	a20_print_string	popal	ret	/************************************************/	/* print ASCIZ string CS:SI (modifies AX BX SI) */	/************************************************/3:	xorw	%bx, %bx	/* video page 0 */	movb	$0x0e, %ah	/* print char in AL */	int	$0x10		/* via TTY mode */a20_print_string:	lodsb	%cs:(%si), %al	/* get token */	cmpb	$0, %al		/* end of string? */	jne	3b	ret	/****************************************/	/* convert AL to hex ascii number in AX */	/****************************************/a20_hex:	movb	%al, %ah	shrb	$4, %al	andb	$0x0F, %ah	orw	$0x3030, %ax	/* least significant digit in AH */	cmpb	$0x39, %ah	jbe	1f	addb	$7, %ah1:	/* most significant digit in AL */	cmpb	$0x39, %al	jbe	1f	addb	$7, %al1:	ret	######################################################################	##	## Routine to empty the 8042 KBC controller. Return ZF=0 on failure.	##	######################################################################empty_8042:	pushl	%ecx	movl	$10000, %ecx	# 100000 is too big4:	call	delay	inb	$0x64, %al	# read 8042 status from port 64h	testb	$1, %al		# is output buffer(data FROM keyboard) full?	jnz	1f		# yes, read it and discard	testb	$2, %al		# is input buffer(data TO keyboard) empty?	jnz	2f		# no, wait until time out	jmp	3f		# both input buffer and output buffer are empty				# success and return with ZF=11:	call	delay		# ZF=0, DELAY should not touch flags!!	inb	$0x60, %al	# read output buffer and discard input				# data/status from 80422:	ADDR32 loop	4b	# ZF=0				# timed out and failure, return with ZF=03:	popl	%ecx	ret	.align	2A20List:	.word	a20_dunno - base_addr	.word	a20_none - base_addr	.word	a20_bios - base_addr	.word	a20_kbc - base_addr	.word	a20_fast - base_addrA20Type:	.word	A20_DUNNO	// default = unknownA20Tries:	.word	0		// Times until giving up on A20	/* Just in case INT 15 might have destroyed the stack... */A20Config:	.word	0		// save original DX hereA20Flags:	.word	0		// save original Flags hereA20ReturnAddress:	.word	0		// save original return address here	/* a20 debug message. 25 backspaces to wipe out the previous	 * "A20 Debug: XXXX trying..." message.	 */A20DbgMsgTry:	.ascii	"\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bA20 Debug: "A20DbgMsgTryHex:	.string	"XXXX trying..."		// null terminated	/* a20 done message. 9 backspaces to wipe out the previous	 * "trying..." message.	 */A20DbgMsgEnd:	.string	"\b\b\b\b\b\b\b\b\bdone! "	// null terminated