[LinuxBIOS] different versions of the GA-M57SLI-S4 (PLCC vs SPI)

Peter Stuge peter at stuge.se
Sun Dec 2 05:48:23 CET 2007

On Sat, Dec 01, 2007 at 07:46:14PM -0500, Richard Smith wrote:
> CS# from the IT8716F is routed up to R509 which is a zero ohm
> resistor.
>   If this resistor is in place then CS is hardwired to CS# on U5
> which is the SPI chip that's loaded.  If you pull R509 then the CS#
> to both chips are free to be selected by (unloaded) Q2,Q43,Q4, and
> Q5 + resistors but I don't have the configuration mapped out.

They would be part of Gigabyte's patented hardware BIOS failover
technology I suppose.

Q4-3 and Q5-3 are both connected to the superio side of R509, so the
emitter if using PNP transistors.

Traces from Q4-1 and Q5-1 both run toward the flash chips so they
would be the collector.

Q4-2 and Q5-2 the base, with R91 before Q4 and R90 before Q5. The
other side of R91 goes to R389 which then goes to Q43-2. The other
side of R90 goes to R86 which then goes to Q2-2.
There are some vias on the traces between R{90,91} and Q{4,5} so they
are connected to something else as well. (But what?) There are also
vias on traces between R{86,389} and Q{2,43}.

Q43 and Q4 are driven at the same time, through R389 and R91
respectively. I wonder what the purpose of Q43 and Q2 is.

The pinout does indeed match e.g. a BC847 PNP transistor in SOT23

R89 is between Q4-1 (U5-CS#?) and a power net, so would be the
pull-up for when Q4 is not driven to select U5.

There is certainly a corresponding resistor for Q5-1 but there's only
a via from the Q5-1 trace so it would have to be tested. My guess is
R130 (directly south of R129) since it's other end goes to U9-CS#.

> It does not look like there is any easy way to re-enable switching
> between the SPI chips since you have to load several missing parts.

The switch mod can be simplified to use existing pads and no pins
have to be lifted from the flash chips anymore.

1. Remove R509.
2. Populate R89 and R130 with 10k or 100k pull-up 0402 resistors.
3. Solder the switch common to Q4-3 and switch between Q4-1 and Q5-1.

Of course this assumes that soldering 0402 resistors is considered
simple, which isn't likely true unless you're good at SMT soldering.

> I'll probably just end up soldering on a 2nd chip and then wiring
> the CS# pins up to a switch like the other mods did.

Of course there could be some timer thingy to do failover, but I
think manual control is best. I think the spring-loaded switch is
as useful as any mechanism in this case.


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