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Merge in timeout into A20-enable routine from cdboot/boot1.

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MFC after:	1 day
This commit is contained in:
Maxim Sobolev 2006-04-11 20:53:49 +00:00
parent 31062da1b0
commit e101181393
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=157669
1 changed files with 10 additions and 3 deletions
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13
sys/boot/i386/pxeldr/pxeldr.S
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@ -227,10 +227,17 @@ putc: movw $0x7,%bx # attribute for output
jmp putstr # keep looping
/*
* Enable A20
* Enable A20. Put an upper limit on the amount of time we wait for the
* keyboard controller to get ready (65K x ISA access time). If
* we wait more than that amount, the hardware is probably
* legacy-free and simply doesn't have a keyboard controller.
* Thus, the A20 line is already enabled.
*/
seta20: cli # Disable interrupts
seta20.1: inb $0x64,%al # Get status
xor %cx,%cx # Clear
seta20.1: inc %cx # Increment, overflow?
jz seta20.3 # Yes
inb $0x64,%al # Get status
testb $0x2,%al # Busy?
jnz seta20.1 # Yes
movb $0xd1,%al # Command: Write
@ -240,7 +247,7 @@ seta20.2: inb $0x64,%al # Get status
jnz seta20.2 # Yes
movb $0xdf,%al # Enable
outb %al,$0x60 # A20
sti # Enable interrupts
seta20.3: sti # Enable interrupts
retw # To caller
/*