[coreboot] BIOS Savior (RD1-PMC4/8X) unavailable? Build my own?

[Andrew Goodbody]

On 09/11/12 06:29, Milo Hoffmann wrote:
> The datasheet does not include the /CE pin from the quick and dirty
> explanation. I interpret it to mean the WE# (Write Enable) pin but am
> seeking confirmation from more informed folks.
>
> Can anyone on the list confirm I could hook up two identical
> SST49LF004B, using the WE# pin, to a three wire switch and have a
> functioning switchable BIOS?

There is no /CE pin because these devices are very different from the 
29F040 that is referenced in the link you gave. Even if they behaved 
similarly, and they don't, then /WE would be the wrong choice, it would 
not affect read operations at all.

The SST49LF040B can operate in two modes. One is called programmer mode 
and is only used by standalone flash programming units. The other mode 
is FirmWare Hub mode (FWH) and this is the mode that is used when the 
chip is actually fitted to a board and so is the one that you must deal 
with. In order to have multiple FWH devices all connected up without 
interfering with each other you give them all a different ID by 
strapping the pins ID[0:3] to different values. So what you could do is 
to wire a switch to change just the bottom ID line, ID0, for each of the 
two devices, strapping one to a '0' and the other to '1', flip the 
switch and invert both values. You can use a DPDT switch for this. 
Connect all other lines 1:1.

Andrew