Date: Wed, 2 Jun 2004 12:55:41 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Nate Lawson <nate@root.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/boot/i386/boot2 boot1.S Message-ID: <200406021255.41118.jhb@FreeBSD.org> In-Reply-To: <20040602093149.D35427@root.org> References: <20040602093847.D53A516A520@hub.freebsd.org> <20040602093149.D35427@root.org>
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On Wednesday 02 June 2004 12:36 pm, Nate Lawson wrote: > On Wed, 2 Jun 2004, Poul-Henning Kamp wrote: > > phk 2004/06/02 02:38:33 PDT > > > > FreeBSD src repository > > > > Modified files: > > sys/boot/i386/boot2 boot1.S > > Log: > > Some embedded platforms have no keyboard controller. Give up waiting > > for it to react after a timeout. > > > > Revision Changes Path > > 1.28 +11 -4 src/sys/boot/i386/boot2/boot1.S > > > > --- src/sys/boot/i386/boot2/boot1.S:1.27 Fri May 14 13:29:29 2004 > > +++ src/sys/boot/i386/boot2/boot1.S Wed Jun 2 02:38:32 2004 > > @@ -197,13 +197,16 @@ > > xorb %al,%al # Zero assumed bss from > > rep # the end of boot2.bin > > stosb # up to 0x10000 > > - callw seta20 # Enable A20 > > - jmp start+MEM_JMP-MEM_ORG # Start BTX > > + > > By removing the callw/retw and moving the jmp to the end, A20 enable can't > be called as a subroutine from elsewhere. Will it be needed elsewhere? No. > > /* > > * 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 > > +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 > > -Nate -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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