MPC83xx watchdog reset board dead lock

[Leon Woestenberg]

Hello,

On Tue, Jun 16, 2009 at 6:30 PM, David Hawkins<dwh at ovro.caltech.edu> wrote:
>> Most MPC8xxx board designs I have seen suffer from this possible dead
>> lock:
>> - NOR Flash is put in erase mode or write mode
>> - Hardware watchdog triggers
>> - HRESET# is asserted by the processor, during which the configuration
>> words are read from NOR Flash.
>>
>> Either
>> HRESET# is not attached to NOR, NOR stays in erase/write mode and
>> invalid words will be read -> dead lock
>>
>> or either:
>> HRESET# is attached to NOR reset, NOR is reset, but stays in reset as
>> HRESET# stays asserted.
>>
>> We have been looking at several solutions hardware wise that reset the
>> NOR flash on HRESET# going low, but the processors are stubborn,
>> read the config words only once, than dead lock.
>>
>> I wonder if there are known-working designs for this.
>
> What do you do in the case of blank flash on a board?
>
The problem is not with blank flash or firmware upgrades, we know how
to handle that.

Your solution is (a solution) to a different problem.

The problem lies in the fact that board dead lock can occur if the
watchdog triggers, for all reference designs I have seen.

Thanks for thinking along.  I would like to solve the original problem though.
BTW, we use CPLD/FPGAs on most of our boards, this one we do not for
cost reasons.


Regards,
-- 
Leon