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Date: Wed, 2 Jun 2004 10:24:38 -0700 (PDT)
From: Nate Lawson <nate@root.org>
To: John Baldwin <jhb@FreeBSD.org>
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cc: cvs-src@FreeBSD.org
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cc: Poul-Henning Kamp <phk@FreeBSD.org>
cc: cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/boot/i386/boot2 boot1.S
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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