Re: Porting RedBoot to a 64MB GRG based board

[Mark Salter <msalter at redhat dot com>]

On Wed, 2005-01-26 at 16:04 +0000, Dan Searle wrote:
> Hi,
> 
> [snip]
> 
> Wednesday, January 26, 2005, 3:41:35 PM, you wrote:
> 
> >> 
> >> Would it be sufficient to just reconfigure the SDRAM init register and
> >> pass exec -c"mem=64M@0x0" to the kernel?
> 
> > Probably.
> 
> I tried this first, as it seemed simpler if it worked, i.e. I don't
> exactly need 64Meg for RedBoot time 32 will do. This is as as long as
> the SDRAM controller is configured correctly and the MMU is setup
> correctly. Shouldn't the Linux kernel override the MMU settings that
> RedBoot sets up?

If you use 'exec' to start the kernel, then the mmu is off before
the kernel/decompressor takes control.

> 
> Anyway, it's not working, I've got RedBoot setting the SDRAM
> controller config reg. correctly, and passed mem=64M@0x0 to the
> kernel, but when I try to allocate all the pages I only manage 7000
> odd, or about 30Megs worth.

RedBoot passes an ATAG_MEM option to the kernel and that is based
on CYGMEM_REGION_ram_SIZE which is defined in the grg include/pkgconf
dir. Not sure if the mem= on command line overrides that (I think
it should, though).

--Mark