[Gllug] error kernel compile

[Richard Jones]

On Wed, Dec 03, 2003 at 01:55:09PM +0000, Dylan wrote:
> On Wednesday 03 December 2003 11:25 am, Pete Ryland wrote:
> > On Tue, Dec 02, 2003 at 08:12:04PM +0000, Richard Jones wrote:
> > > As to what happens to the first 640K, I would assume it gets used
> > > just like any other paged memory. In fact I'd be annoyed if it
> > > didn't :-) I hope someone else can give us the right answer to that
> > > question.
> >
> > Indeed, the 640k barrier is only significant in "real mode", and
> > hence only an issue at bootup.  Of course there will be holes in it
> > (e.g. 0xa0000 and 0xb8000 are video memory) but it can otherwise be
> > allocated normally.
> 
> Is the 'old' 640K - 1M memory map still relevant now that things like 
> graphics and sound cards have their own memory and (in some cases) 
> processors and DMA capabilities?

If you're using plain old text mode (not framebuffers) then you very
much need that hole at 0xb8000.

I believe (but don't know for sure) that the other pages should be
available. This is what the BIOS says at boot time, with my comments
preceeded by '>'.

BIOS-provided physical RAM map:
 BIOS-e820: 0000000000000000 - 00000000000a0000 (usable)

>	^^ This is the 0 - 640K memory, available, followed by:
>	a0000 - f0000 : Part of the 640K - 1MB hole.

 BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)

>	^^ This is the rest of that hole. On original PCs, this used to
>	be where the ROM basic was stored. Original 8086s booted at
>	address ffffe IIRC. (Does anyone remember what the exact segment:
>	offset was?)

 BIOS-e820: 0000000000100000 - 000000001dff0000 (usable)

>	^^ This is the main bit of memory, from 1 MB to just under 480 MB.

 BIOS-e820: 000000001dff0000 - 000000001dff3000 (ACPI NVS)
 BIOS-e820: 000000001dff3000 - 000000001e000000 (ACPI data)

>	^^ This is my video card's "video memory" (borrowed from system
>	memory, because this is cheap on-motherboard video).

 BIOS-e820: 00000000ffff0000 - 0000000100000000 (reserved)

>	^^ Anyone's guess why the BIOS has reserved this.

479MB LOWMEM available.

Rich.

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