Problems with ST NAND512W3A nand flash

[MikeW]

Savin Zlobec <savinz <at> users.sourceforge.net> writes:

> 
> Hi All!
> 
> I am working on a AT91RM9200 based board with ST NAND512W3A2B flash.
> Kernel version is 2.6.19.7 with patches from maxim.org.za/at91_26.html.
> Everything works perfectly, except for boot time NAND chip
> identification which fails every once in a while. NAND signature
> is 0x20 0x76, but sometimes I get 0x20 0x20. My first guess was
> timing problems, but I've double checked everything and all signals
> are inside the specs. I've also tested the chip with shorter and
> longer setup, hold and pulse times for read and write, but without
> any success. Trying different kernels didn't help either.
> 
> Any ideas and/or comments would be very much appreciated.
> 
> Thanks,
> savin

a) power supply tolerance; psu noise ?
b) is the second 0x20 a 'repeat' of the first ? in which case will an
extra read give you the required 0x76 ? [if chipid==mfrid reread chipid]
May be a chip problem - it does happen !

MikeW