Help for init value of SRAM in MPC 562

[Sudhersan Lal]

Hello Everyone
Anybody know or can help me to find out more information regarding the initialization value of SRAM contents during power up .
I would like to save some values in sram so that I can read that back after a reset , for eg  saving a byte value and its compliment  and check the consistency between these two variables . This would make sure that, the value is really what I saved prior to reset and not the garbage value which would appear in the memory after a power up.
Any existing behavior known for mpc microcontrollers related to this?
if it is stored like the value and its compliment , what  is the probability of the random initial values in two bytes to be compliment of each other  and mistaken as the good value    
Regards
Sudhersan
 


     

[Non-text portions of this message have been removed]

[Randall Young]

It is definitely possible to find different values in SRAM at power-on.  Some are more common than others, but short power outages can change just a few bits.

I would suggest using a 32 bit CRC rather than a single inverted byte.  That greatly reduces the chances of an error not being detected (although still not zero).

Randall Young
Sr Software Engineer
Navcom Technology, Inc.
A John Deere Company

> -----Original Message-----
> From: MPC500@... [mailto:MPC500@...] On Behalf Of
> Sudhersan Lal
> Sent: Tuesday, July 01, 2008 8:43 PM
> To: MPC500@...
> Subject: [MPC500] Help for init value of SRAM in MPC 562
>
> Hello Everyone
> Anybody know or can help me to find out more information regarding the
> initialization value of SRAM contents during power up .
> I would like to save some values in sram so that I can read that back
> after a reset , for eg  saving a byte value and its compliment  and check
> the consistency between these two variables . This would make sure that,
> the value is really what I saved prior to reset and not the garbage value
> which would appear in the memory after a power up.
> Any existing behavior known for mpc microcontrollers related to this?
> if it is stored like the value and its compliment , what  is the
> probability of the random initial values in two bytes to be compliment of
> each other  and mistaken as the good value
> Regards
> Sudhersan
>

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[Geoff Field]

Hi Sudhersan,

I'm not working with MPC500-series chips at the moment, but the usual
approach is to declare/use a "non-init" segment.  Most compilers will
generate startup code that initialises all RAM apart from the non-init
segment.

I'm not sure of the details for doing this on your specific platform
(compiler, in particular).  However, your compiler manual should
contain something on the subject.

As an alternative, you could tweak the startup code itself to skip a
certain location(s).  Not recommended, but often done.

Geoff

--- In MPC500@..., Sudhersan Lal <sudhersanl@...> wrote:
>
> Hello Everyone
> Anybody know or can help me to find out more information regarding
the initialization value of SRAM contents during power up .
> I would like to save some values in sram so that I can read that
back after a reset , for eg  saving a byte value and its compliment
and check the consistency between these two variables . This would
make sure that, the value is really what I saved prior to reset and
not the garbage value which would appear in the memory after a power up.
> Any existing behavior known for mpc microcontrollers related to this?
> if it is stored like the value and its compliment , what  is the
probability of the random initial values in two bytes to be compliment
of each other  and mistaken as the good value    
> Regards
> Sudhersan