cvs commit: src/sys/boot/i386/boot2 boot1.S
nate at root.org
Wed Jun 2 10:24:38 PDT 2004
On Wed, 2 Jun 2004, John Baldwin wrote:
> On Wednesday 02 June 2004 12:36 pm, Nate Lawson wrote:
> > On Wed, 2 Jun 2004, Poul-Henning Kamp wrote:
> > > /*
> > > * Enable A20 so we can access memory above 1 meg.
> > > + * Use the zero-valued %cx as a timeout for embedded hardware which do
> > > not + * have a keyboard controller.
> > > */
> > > seta20: cli # Disable interrupts
> > > -seta20.1: inb $0x64,%al # Get status
> > Should be a "movw TIMEOUT, %cx" here. (Or whatever the timeout constant
> > is.)
> xor %cx,%cx is smaller
Ah, I thought a timeout less than 65535 was desirable.
> > > +seta20.1: dec %cx # Timeout?
> > > + jz seta20.3 # Yes
> > > + inb $0x64,%al # Get status
> > > testb $0x2,%al # Busy?
> > > jnz seta20.1 # Yes
> > > movb $0xd1,%al # Command: Write
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