diff options
Diffstat (limited to 'ldlinux.asm')
| -rw-r--r-- | ldlinux.asm | 34 |
1 files changed, 26 insertions, 8 deletions
diff --git a/ldlinux.asm b/ldlinux.asm index c15e9b19..9185bec2 100644 --- a/ldlinux.asm +++ b/ldlinux.asm @@ -341,6 +341,7 @@ InitRDCNameLen resw 1 ; Length of unmangled initrd name NextCharJump resw 1 ; Routine to interpret next print char SetupSecs resw 1 ; Number of setup sectors SavedSP resw 1 ; Our SP while running a COMBOOT image +A20test resw 1 ; Counter for testing status of A20 TextAttrBX equ $ TextAttribute resb 1 ; Text attribute for message file TextPage resb 1 ; Active display page @@ -2300,8 +2301,8 @@ bcopy: ; ; We typically toggle A20 twice for every 64K transferred. ; -%define io_delay out 080h,al ; Invalid port (we hope) -%define delaytime 1024 ; ISA bus cycles (1.5 µs) +%define io_delay times 4 out 0EDh,al ; Invalid port (we hope) +%define delaytime 256 ; 4 x ISA bus cycles (@ 1.5 µs) enable_a20: call empty_8042 @@ -2310,12 +2311,21 @@ enable_a20: call empty_8042 mov al,0DFh ; A20 on out 060h, al -kbc_delay: call empty_8042 - push cx - mov cx, delaytime -.delayloop: io_delay - loop .delayloop - pop cx + call kbc_delay + ; 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 + mov ax,0FFFFh ; HMA + mov es,ax +.a20_wait: inc word [ss:A20test] + mov ax,[es:A20test+10h] + cmp ax,[ss:A20test] + je .a20_wait + pop es ret disable_a20: @@ -2327,6 +2337,14 @@ disable_a20: out 060h, al jmp short kbc_delay +kbc_delay: call empty_8042 + push cx + mov cx, delaytime +.delayloop: io_delay + loop .delayloop + pop cx + ret + empty_8042: io_delay in al, 064h ; Status port |