[LinuxBIOS] flashrom support for AMD CS5536

Alan Alexander alan at IceraSemi.com
Fri Nov 23 19:22:43 CET 2007

Many thanks for the information. Unfortunately I don't have access to
the board schematics and getting technical support from the board
supplier is proving rather difficult.

I have confirmed via an oscilloscope that both the WP# and TBL# pins are
permanently pulled high - indicating that no hardware write protection
is enabled (so it looks like I may have side stepped the GPIO locking
issue). I have also observed activity on the LFRAME#/FWH4 pin when
flashrom is attempting to write to the flash. Since I don't have access
to X-ray equipment I think my best shot is to take a look at waveforms
produced during a byte program cycle. I just need to get hold of that
Logic Analyzer.......

Best regards,


Alan Alexander          mailto:alan at icerasemi.com
Software Toolchain Engineering
Icera Inc, 2520 The Quadrant, Aztec west, Bristol BS32 4AQ, UK
Tel. +44 (0)1454 284805 
-----Original Message-----
From: bari [mailto:bari at onelabs.com] 
Sent: 23 November 2007 17:15
To: Alan Alexander
Cc: linuxbios at linuxbios.org
Subject: Re: [LinuxBIOS] flashrom support for AMD CS5536

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
> 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
> and TBL# (Top-Block-Lock) which enables hardware write protection of
> 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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