[coreboot] [PATCH] xcshell: serial shell for early debugging

Michael Gold mgold at ncf.ca
Wed Jul 15 01:17:40 CEST 2009

On Tue, Jul 14, 2009 at 21:51:51 +0200, Carl-Daniel Hailfinger wrote:
> > I think it might be possible without any changes by marking the part of
> > the ROM containing xcshell as cacheable, and then using pokes to rewrite
> > the rest of the chip.  It would be slow, but a small flash upgrade
> > program could be uploaded that would do the rest of the work more
> > quickly.
> >   
> If you have a generic "write X to loation y" interface, flashrom can
> deal with that, even remotely.

That interface exists.  I guess you'd need to execute xcshell from RAM,
or use the --estart and --eend options to exclude the portion of the ROM
it's executing from.

> > My original idea was that one would set up CAR, upload code, and jump to
> > it; this would allow the system to be extended without having to include
> > much code.  It doesn't work, at least on my Pentium 3, but the same
> > thing could be done with RAM once it's initialised (or with flash for
> > occasional use).
> >   
> As long as RAM works, we could even upload a complete flashrom binary
> over zmodem.

I don't have zmodem support currently.  It would be easy to add a
command that writes both 32-bit operands to RAM, using the accumulator
as the pointer (auto-incremented afterwards).  Then only 3 of 11 bytes
would be protocol overhead, which should be fine if the binary isn't too
large.  Adding an automatic increment to peekl and pokel might be useful
as well.

-- Michael
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