Date: Wed, 2 Jun 2004 10:24:38 -0700 (PDT) From: Nate Lawson <nate@root.org> To: John Baldwin <jhb@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/boot/i386/boot2 boot1.S Message-ID: <20040602102252.U35868@root.org> In-Reply-To: <200406021255.41118.jhb@FreeBSD.org> References: <20040602093847.D53A516A520@hub.freebsd.org> <20040602093149.D35427@root.org> <200406021255.41118.jhb@FreeBSD.org>
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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
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