diff options
Diffstat (limited to 'pxelinux.asm')
| -rw-r--r-- | pxelinux.asm | 102 |
1 files changed, 69 insertions, 33 deletions
diff --git a/pxelinux.asm b/pxelinux.asm index 5734ea3a..39f5a93a 100644 --- a/pxelinux.asm +++ b/pxelinux.asm @@ -8,7 +8,7 @@ ; network booting API. It is based on the SYSLINUX boot loader for ; MS-DOS floppies. ; -; Copyright (C) 1994-1999 H. Peter Anvin +; Copyright (C) 1994-2000 H. Peter Anvin ; ; 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 @@ -365,6 +365,7 @@ RetryCount resb 1 ; Used for disk access retries KbdFlags resb 1 ; Check for keyboard escapes LoadFlags resb 1 ; Loadflags from kernel A20Tries resb 1 ; Times until giving up on A20 +A20KBCflag resb 1 ; Did we use KBC to access A20? FuncFlag resb 1 ; == 1 if <Ctrl-F> pressed alignb tftp_port_t_size @@ -2043,18 +2044,16 @@ bcopy: push eax slow_out: out dx, al ; Fall through -_io_delay: push ax - in ax,IO_DELAY_PORT - in ax,IO_DELAY_PORT - in ax,IO_DELAY_PORT - in ax,IO_DELAY_PORT - pop ax +_io_delay: out IO_DELAY_PORT,al + out IO_DELAY_PORT,al + out IO_DELAY_PORT,al + out IO_DELAY_PORT,al ret enable_a20: mov byte [ss:A20Tries],255 ; Times to try to make this work -try_enable_a20: +.try_enable_a20: ; ; Flush the caches ; @@ -2063,44 +2062,46 @@ try_enable_a20: ; ; Enable the "fast A20 gate" ; + mov byte [ss:A20KBCflag], 0 ; Haven't used the KBC yet in al, 092h or al,02h + and al,~01h ; Don't accidentally reset the machine! out 092h, al ; ; Enable the keyboard controller A20 gate ; + mov dl, 1 ; Allow early exit call empty_8042 - mov al,0D1h ; Command write + jnz .a20_wait ; A20 live, no need to use KBC + + mov byte [ss:A20KBCflag], 1 ; We touched the KBC + mov al,0D1h ; Command write out 064h, al - call empty_8042 + call empty_8042_uncond + mov al,0DFh ; A20 on out 060h, al - call kbc_delay + call empty_8042_uncond + ; Verify that A20 actually is enabled. Do that by ; observing a word in low memory and the same word in ; the HMA until they are no longer coherent. Note that ; we don't do the same check in the disable case, because ; we don't want to *require* A20 masking (SYSLINUX should ; work fine without it, if the BIOS does.) - push es - push cx - mov cx,0FFFFh ; Times to try, also HMA - mov es,cx ; HMA = segment 0FFFFh -.a20_wait: inc word [ss:A20Test] - call try_wbinvd - mov ax,[es:A20Test+10h] - cmp ax,[ss:A20Test] - jne .a20_done - loop .a20_wait +.a20_wait: push cx + mov cx, 0FFFFh +.a20_wait_loop: + call a20_test + jnz .a20_done + loop .a20_wait_loop ; ; Oh bugger. A20 is not responding. Try frobbing it again; eventually give up ; and report failure to the user. ; pop cx - pop es - dec byte [ss:A20Tries] - jnz try_enable_a20 + jnz .try_enable_a20 mov si, err_a20 jmp abort_load @@ -2108,6 +2109,27 @@ try_enable_a20: ; A20 unmasked, proceed... ; .a20_done: pop cx + ret + +; +; This routine tests if A20 is enabled (ZF = 0). This routine +; must not destroy any register contents. +; +a20_test: + push es + push cx + push ax + mov cx,0FFFFh ; HMA = segment 0FFFFh + mov es,ax + mov cx,0100h ; Loop count + mov ax,[ss:A20Test] +.a20_wait: inc ax + mov [ss:A20Test],ax + call try_wbinvd + cmp ax,[es:A20Test+10h] + loopz .a20_wait +.a20_done: pop ax + pop cx pop es ret @@ -2120,29 +2142,43 @@ disable_a20: ; Disable the "fast A20 gate" ; in al, 092h - and al,~02h + and al,~03h out 092h, al ; ; Disable the keyboard controller A20 gate ; - call empty_8042 + test [ss:A20KBCflag], byte 01h + jz .snooze ; Never messed with the KBC + + ; We did mess with the KBC, so we have to do this.. + call empty_8042_uncond mov al,0D1h out 064h, al ; Command write - call empty_8042 + call empty_8042_uncond mov al,0DDh ; A20 off out 060h, al - ; Fall through/tailcall to kbc_delay - -kbc_delay: call empty_8042 - push cx + call empty_8042_uncond + ; Wait a bit for it to take effect +.snooze: push cx mov cx, delaytime .delayloop: io_delay loop .delayloop pop cx ret +; +; Routine to empty the 8042 KBC controller. If dl != 0 +; then we will test A20 in the loop and exit if A20 is +; suddenly enabled. +; +empty_8042_uncond: + xor dl,dl empty_8042: - io_delay + call a20_test + jz .a20_on + and dl,dl + jnz .done +.a20_on: io_delay in al, 064h ; Status port test al,1 jz .no_output @@ -2153,7 +2189,7 @@ empty_8042: test al,2 jnz empty_8042 io_delay - ret +.done: ret ; ; WBINVD instruction; gets auto-eliminated on 386 CPUs |