[LinuxBIOS] SPD as debug channel

Peter Stuge stuge-linuxbios at cdy.org
Sun Dec 3 19:08:33 CET 2006

On Fri, Dec 01, 2006 at 11:21:15PM +0100, Segher Boessenkool wrote:
> > If not, what IS easily accessible besides the boot ROM?
> In general?  Nothing, not necessarily the boot ROM even!

I was trying to think outside the box. Is there any way to affect the
system in a way that is easy to measure? Power? Voltage? Any bit that
is easy to tap works. It must not be intended for communication, a
side-effect is fine, as long as it is portable. (Ie. certain
instructions executed in a certain order => CPU draws more power.)
A bit wild, but simple to implement.

> >> I think that we are going into a world where we have to figure
> >> out usb debug port.
> >
> > It's certainly one good debugging option but maybe not the only
> > good one.
> And *all* these options require special (extra) debug hardware,
> no good for the end user.

We have to make sure the code never fails that early then. He-he.

> >> I don't think that the PCI initial setup for USB debug is going to
> >> be impossible -- the vendors have to debug these boards too. All
> >> the boards I have used lately have a very straightforward path to
> >> USB, that could be set up in the ROMCC or CAR code.
> >
> > I think it should be fairly simple on x86 too,
> It can't be done in a generic way.

This is an interesting topic. See other thread about RAM.


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