; ; A20.ASM -- Control the A20 gate ; ; Copyright (c) 1991-1995 by Eberhard Mattes ; ; This file is part of emx. ; ; emx 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, or (at your option) ; any later version. ; ; emx 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 emx; see the file COPYING. If not, write to ; the Free Software Foundation, 59 Temple Place - Suite 330, ; Boston, MA 02111-1307, USA. ; ; See emx.asm for a special exception. ; INCLUDE EMX.INC INCLUDE XMS.INC INCLUDE VCPI.INC INCLUDE OPTIONS.INC PUBLIC USE_A20_PATCH, USE_FAST_A20 PUBLIC INIT_A20, CLEANUP_A20, CHECK_A20 PUBLIC A20_ON, A20_OFF SV_DATA SEGMENT ; ; Enable/disable A20: address of functions ; A20_ON_JMP DW ? A20_OFF_JMP DW ? A20_FLAG DB FALSE USE_A20_PATCH DB FALSE USE_FAST_A20 DB FALSE SV_DATA ENDS INIT_CODE SEGMENT ASSUME CS:INIT_CODE, DS:NOTHING ; ; Find out which machine we're running on ; and set A20 enable/disable function addresses ; ASSUME DS:SV_DATA INIT_A20 PROC NEAR PUSH ES ; Don't clobber ES (ARGS!) LEA BX, PATCH_A20_ON LEA DX, PATCH_A20_OFF CMP USE_A20_PATCH, FALSE JNE SHORT INIT_A20_SET LEA BX, FAST_A20_ON LEA DX, FAST_A20_OFF CMP USE_FAST_A20, FALSE JNE SHORT INIT_A20_SET LEA BX, XMS_A20_ON LEA DX, XMS_A20_OFF CMP XMS_FLAG, FALSE JNE SHORT INIT_A20_SET LEA BX, FMR70_A20_ON LEA DX, FMR70_A20_OFF CMP MACHINE, MACH_FMR70 JE SHORT INIT_A20_SET LEA BX, PC98_A20_ON LEA DX, PC98_A20_OFF CMP MACHINE, MACH_PC98 JE SHORT INIT_A20_SET LEA BX, INBOARD_A20_ON LEA DX, INBOARD_A20_OFF CMP MACHINE, MACH_INBOARD JE SHORT INIT_A20_SET MOV AH, 0C0H ; Return config. parameters STC ; Don't trust BIOS INT 15H ; `Cassette I/O' JC SHORT INIT_A20_1 ; Cannot happen, assume AT MOV AL, ES:[BX+5] ; Get flags byte TEST AL, 00000010B ; Micro Channel? JZ SHORT INIT_A20_1 ; No -> AT compatible ; ; It's a PS/2 ; CALL PS2_A20_OFF ; Turn off A20 LEA BX, PS2_A20_ON ; Why? HIMEM.SYS does LEA DX, PS2_A20_OFF JMP SHORT INIT_A20_SET ; ; It's an AT compatible machine ; INIT_A20_1: LEA BX, AT_A20_ON LEA DX, AT_A20_OFF INIT_A20_SET: CMP VCPI_FLAG, FALSE ; VCPI ? JE SHORT INIT_A20_SET_1 ; No -> skip LEA BX, NO_A20_ON ; Don't enable A20 LEA DX, NO_A20_OFF ; Don't disable A20 INIT_A20_SET_1: MOV A20_ON_JMP, BX MOV A20_OFF_JMP, DX POP ES RET INIT_A20 ENDP DATA_8042 = 60H ; Keyboard processor STATUS_8042 = 64H ; Keyboard processor ; ; Enable address line A20 ; ; Note: disables interrupts ; ASSUME DS:SV_DATA A20_ON PROC NEAR PUSH AX CLI CALL A20_ON_JMP MOV A20_FLAG, NOT FALSE POP AX RET A20_ON ENDP ; ; Disable address line A20 ; ; Note: disables interrupts ; ASSUME DS:SV_DATA A20_OFF PROC NEAR PUSH AX CLI CALL A20_OFF_JMP MOV A20_FLAG, FALSE POP AX RET A20_OFF ENDP ; ; Don't enable address line A20 ; NO_A20_ON PROC NEAR RET NO_A20_ON ENDP ; ; Don't disable address line A20 ; NO_A20_OFF PROC NEAR RET NO_A20_OFF ENDP ; ; Enable address line A20 (AT compatible) ; AT_A20_ON PROC NEAR MOV AH, 0DFH CALL AT_SET_A20 RET AT_A20_ON ENDP ; ; Disable address line A20 (AT compatible) ; AT_A20_OFF PROC NEAR MOV AH, 0DDH CALL AT_SET_A20 RET AT_A20_OFF ENDP ; ; Enable address line A20 (PS/2) ; PS2_A20_ON PROC NEAR IN AL, 92H OR AL, 02H OUT 92H, AL RET PS2_A20_ON ENDP ; ; Disable address line A20 (PS/2) ; PS2_A20_OFF PROC NEAR IN AL, 92H AND AL, NOT 02H OUT 92H, AL RET PS2_A20_OFF ENDP ; ; Enable address line A20 (Inboard 386/PC) ; INBOARD_A20_ON PROC NEAR MOV AL, 0DFH OUT 60H, AL RET INBOARD_A20_ON ENDP ; ; Disable address line A20 (Inboard 386/PC) ; INBOARD_A20_OFF PROC NEAR MOV AL, 0DDH OUT 60H, AL RET INBOARD_A20_OFF ENDP ; ; Enable/disable address line A20 (AT compatible) ; ; In: AL=0DDH Disable ; AL=0DFH Enable ; AT_SET_A20 PROC NEAR PUSH CX CALL READY_8042 JNZ SHORT AT_SET_A20_END MOV AL, 0D1H ; Write output port OUT STATUS_8042, AL CALL READY_8042 JNZ SHORT AT_SET_A20_END MOV AL, AH ; Data OUT DATA_8042, AL CALL READY_8042 MOV AL, 0FFH ; Pulse nothing (just wait) OUT STATUS_8042, AL CALL READY_8042 AT_SET_A20_END: POP CX RET AT_SET_A20 ENDP ; ; Wait until we can send a command to the keyboard controller ; READY_8042 PROC NEAR XOR CX, CX TALIGN 4 ; Avoid surprises READY_1: IN AL, STATUS_8042 TEST AL, 02H ; Input buffer full? LOOPNZ READY_1 ; Yes -> wait RET READY_8042 ENDP FAST_IO_DELAY MACRO LOCAL L1, L2 JMP SHORT L1 L1: JMP SHORT L2 L2: ENDM ; ; Enable address line A20 (fast) ; FAST_A20_ON PROC NEAR MOV AL, 0D1H OUT STATUS_8042, AL FAST_IO_DELAY MOV AL, 0DFH ; Enable OUT DATA_8042, AL RET FAST_A20_ON ENDP ; ; Disable address line A20 (fast) ; FAST_A20_OFF PROC NEAR MOV AL, 0D1H OUT STATUS_8042, AL FAST_IO_DELAY MOV AL, 0DDH ; Disable OUT DATA_8042, AL RET FAST_A20_OFF ENDP ; ; Enable address line A20 (Fujitsu FMR70) ; FMR70_A20_ON proc near MOV AL, 00110000B OUT 20H, AL RET FMR70_A20_ON ENDP ; ; Disable address line A20 (Fujitsu FMR70) ; FMR70_A20_OFF PROC NEAR MOV AL, 0 OUT 20H, AL RET FMR70_A20_OFF ENDP ; ; Enable address line A20 (NEC PC-98) ; PC98_A20_ON PROC NEAR MOV AL, 0 OUT 0F2H, AL RET PC98_A20_ON ENDP ; ; Disable address line A20 (NEC PC-98) ; PC98_A20_OFF PROC NEAR MOV AL, 0FFH OUT 0F2H, AL RET PC98_A20_OFF ENDP ; ; Enable address line A20 (patched) ; PATCH_A20_ON PROC NEAR RET DB "PATCH_A20_ON " RET PATCH_A20_ON ENDP ; ; Disable address line A20 (patched) ; PATCH_A20_OFF PROC NEAR RET DB "PATCH_A20_OFF" RET PATCH_A20_OFF ENDP ; ; ; ASSUME DS:SV_DATA CLEANUP_A20 PROC NEAR CMP A20_FLAG, FALSE JE SHORT CA20_RET CALL A20_OFF CA20_RET: RET CLEANUP_A20 ENDP ; ; Check if A20 is enabled ; ; Returns AX=0 iff A20 is disabled ; ; Note: disables interrupts ; ASSUME DS:SV_DATA CHECK_A20 PROC NEAR PUSH DS PUSH ES MOV AX, 1 ; Assume A20 is enabled CMP VCPI_FLAG, FALSE ; VCPI active? JNE SHORT CKA20_RET ; Yes -> done MOV AX, 0000H MOV DS, AX ; We compare data at 0000:0000 ASSUME DS:NOTHING MOV AX, 0FFFFH ; to data at FFFF:0010 MOV ES, AX CLI ; Avoid unexpected things MOV AX, DS:[00H] ; (Divide exception) XOR AX, ES:[10H] ; Equal contents? JNZ SHORT CKA20_RET ; No -> A20 on (or no mem) NOT WORD PTR DS:[00H] ; Change word at 0000:0000 MOV AX, DS:[00H] ; Get new value XOR AX, ES:[10H] ; Still equal contents? NOT WORD PTR DS:[00H] ; Restore word at 0000:0000 CKA20_RET: POP ES POP DS RET CHECK_A20 ENDP INIT_CODE ENDS END