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Date: Thu, 05 Apr 2012 13:39:26 +0200
From: Oliver Schinagl <oliver+list AT schinagl DOT nl>
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To: geda-user AT delorie DOT com
CC: Colin D Bennett <colin AT gibibit DOT com>
Subject: Re: [geda-user] Re: [coreboot] Dual SPI Flash adapter
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Reply-To: geda-user AT delorie DOT com

On 04/05/12 01:38, Colin D Bennett wrote:
> Hi Oliver,
>
> Your project sounds interesting, but I don't yet understand it
> completely.  You mentioned it can be useful for coreboot (PC
> firmware) development if the dual SPI flash module is installed on
> the motherboard.  Could you elaborate on that?  I am not familiar
> with coreboot.
Coreboot is a bios replacement, that is fully open source.

There are certain motherboards that have 'dual bios' capability, in case 
the user bricks his bios, by flashing something wrong. Overclockers tend 
to do that often, trying out random bioses because it may over some 
weird option or the like.

Generally, it is not a bad idea, to offer this on a motherboard anyway, 
allows a user to quickly swap between two biosses (old version and new 
version) and BoM can't be that big of a difference, not on a high end 
motherboard anyway.
>
> Do existing motherboards include a _single_ SPI flash IC already?
I've noticed all my newer Asus motherboards now use an DIP8 SPI Flash IC.

> What is stored on the SPI flash, and who reads data from it?
Well the bios binary is stored int he SPI flash :)

> Is your module designed to mount on a stock motherboard and
> transparently emulate a single SPI flash IC, or does it use a
> modified interface (presumably requiring the party accessing it to
> be modified?
It plugs into the DIP8 socket of the motherboard, and you can insert 
your original DIP8 bios chip ontop of the adapter. Onboard of the 
adapter there is a SOIC8 chip. All pins of an SPI IC, work like a bus, 
so everything can be connected together, with the exception of the 'chip 
select' pin. By tying it to GND, it is activated. So by using a jumper 
on JP1 (or a switch, or a long wire and a switch) a user can then swap 
bioses (Or rather chips) while the PC is running even (hot swapping).

This is quite usefull when doing coreboot developement or testing if a 
new bios works for you. Boot your normal bios, swap the jumper/flip the 
switch, write a new bios to your 'other' chip and reboot. (I've heard 
some biosses don't like to not shutdown with a bios that you did not 
boot up with so you'd have to swap the jumper back when shutting down 
again).


The idea arose browsing the coreboot website and saw some people have 
actually done this not only with DIP8 packages, but also older bigger 
bios chips. Ontop of that I had a hard time finding big DIP8 IC's with 
SOIC8 being around plentyfull. :)
>
> Regards,
> Colin

So summarized, it's a poor mans 'dual bios' adapter.
I hope that clears things up a bit :D

Oliver