Question about AGP (epia-m)

Dave Ashley linuxbios at
Tue Jun 22 13:38:00 CEST 2004

>I haven't implemented this yet within linuxbios V1 but I will try it out and
>post again.

It's pretty irritating. When I turn 00.0 byte $88 bit 1 to 1, the MB
locks up. Turning that bit on enables the graphics aperture. I'm going to
just do it in a userspace program, which works fine.

I can put this in V1 src/mainboard/via/epia-m/ at the top:
// set AGP aperture size to 128M
	movl	$CONFIG_ADDR(0, 0x00, 0x84), %eax
	movb	$0x80, %dl
// enable AGP
	movl	$CONFIG_ADDR(0, 0x00, 0xa9), %eax
	movb	$0x01, %dl
// Move AGP to safe place before enabling
	movl	$CONFIG_ADDR(0, 0x00, 0x10), %eax
	movl	$0xe0000000,%edx

However if I follow this with
	movl	$CONFIG_ADDR(0, 0x00, 0x88), %eax
	movb	$2,%dl

Then it locks up. I had thought it might be because the GART is supposed
to be in system memory, so if I try and turn it on before DRAM is ready, the
AGP system might try to read a page of the GART into its cache, and this
results in a fault since the memory isn't there. So I tried doing the last
turn on bit later after DRAM is initialized, but that didn't help.


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