[LinuxBIOS] flashrom support for AMD CS5536

bari bari at onelabs.com
Fri Nov 23 18:15:27 CET 2007

Alan Alexander wrote:
> My mistake - that patch hasn't made a difference to the behaviour.
> It looks to me as if I'm unable to write to the top-block of the
> Pm49FL004 device. Looking at the data sheet it appears that this device
> has 2 write-protect pins - WP# (which looks as if it's wired up to the
> AMD C5536 appropriately - such that writes to MSR 0x1808 have an effect)
> and TBL# (Top-Block-Lock) which enables hardware write protection of the
> top boot block (64Kbytes). Unfortunately I don't know how the TBL# pin
> is connected to the CS5536. I'm guessing a GPIO.
> Does anyone have any experience of using this BIOS flash with the
> CS5536?

There is no "standard" or "required" way to connect the Top-Block-Lock 
pin to the CS5536. The board designers may have followed the AMD 
reference schematics or have done any number of other things with the 
signal. It appears that you don't have the schematics for the board. Try 
contacting tech support for your board and ask them if they know.

Is there a jumper on the board to control writes to Flash?

You may be able to trace the connections using a multimeter if they used 
thru and not blind vias under the CS5536. X-raying the board may also 
help, if you have access to the equipment.

To make things more interesting many of the GPIO's on the CS5536 have 
Lock Bit registers to protect against accidental changes.

Since TBL# is probably pulled up to high via a 4K-10K resistor, you 
could temporarily solder a connection from the TBL# to ground to enable 
it. Then you can test if you can write to the flash.


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