[LinuxBIOS] SPI flash focus

Segher Boessenkool segher at kernel.crashing.org
Sat Nov 25 02:49:32 CET 2006

> If grounding HOLD# at power-on is working for people so far, that's
> great to hear.

You don't even *need* a BIOS-saviour like solution like
this; SPI flash chips are quite easy to program in-system
(if the system is designed correctly), either with the
board powered on or off.

> The SST datasheet implies that this is not the specified behavior, in
> fact my reading is that HOLD# is only sampled on SCK, and with CE# low.

HOLD# makes the flash chip not drive SO, and it would only do that on
SCK with CE# selected anyway.  What am I missing?

> If the chipset drives HOLD# directly, though, it gets a little messier;
> then it may be best to put a tristate-able buffer on the SO8-clip and
> overdrive the mobo's SPI flash signals for the 1-2 seconds needed to
> rewrite the whole thing,

It's more like 10 seconds per megabyte, with a fast SPI interface.

> tristating as soon as the write is finished.
> That starts to require a pretty fast interface, driven over a cable, 
> and
> now it's a lot messier than simply hotswapping a PLCC chip!

In-circuit programming is a lot easier, heh.  Many boards have a
header for this btw, no clip needed.  The manufacturers have
similar problems during manufacturing you know :-)


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