Re: MPC5566 SRAM ECC

"allandobbin2000" <[email protected]> Fri, 13 Nov 2009 15:38:54 -0000
Newsgroups	gmane.comp.hardware.motorola.microcontrollers
Message-ID	<[email protected]>
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While its true the SRAM contents don't change after a RESET and therefore t=
here is no need to re-init the ECC, it is NOT true that the ECC has been in=
itialised if PORS if zero. For instance you could have a power cycle immedi=
ately followed by a RESET and the ECC may not yet be initialised.

A safer method is to use a few words in SRAM and store a constant after the=
 ECC has been initialised.  Then after subsequent resets, you verify the PO=
RS flag and the constant in SRAM - if PORS is set, OR if the constant data =
isn't valid then you init the ECC.

There are still dangers with this i.e. make sure you don't use standy RAM f=
or storing the constant.  Also, if the ECC isn't intact, you may generate a=
n ECC related error when reading your constant.

Make sure you ask yourself what possible RESET sources you expect and what =
start-up time you have to meet - if you don't really expect a reset other t=
han a POR, just init the ECC every time as its safer.

- Allan

--- In [email protected], <StevenASchroeder@...> wrote:
>
> Is it correct that I only need to initialize the SRAM ECC after a
> power-on reset?  That is, if SIU_RSR[PORS] is zero I can skip the SRAM
> ECC initialization.
>=20
>=20=20
>=20
> Thanks,
>=20
> Steve
>=20
>=20
>=20
> [Non-text portions of this message have been removed]
>



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      <p>While its true the SRAM contents don't change after a RESET and therefore there is no need to re-init the ECC, it is NOT true that the ECC has been initialised if PORS if zero. For instance you could have a power cycle immediately followed by a RESET and the ECC may not yet be initialised.<br>
<br>
A safer method is to use a few words in SRAM and store a constant after the ECC has been initialised.  Then after subsequent resets, you verify the PORS flag and the constant in SRAM - if PORS is set, OR if the constant data isn't valid then you init the ECC.<br>
<br>
There are still dangers with this i.e. make sure you don't use standy RAM for storing the constant.  Also, if the ECC isn't intact, you may generate an ECC related error when reading your constant.<br>
<br>
Make sure you ask yourself what possible RESET sources you expect and what start-up time you have to meet - if you don't really expect a reset other than a POR, just init the ECC every time as its safer.<br>
<br>
- Allan<br>
<br>
--- In <a href="mailto:MPC500%40yahoogroups.com">MPC500@yahoogroups.<wbr>com</a>, &lt;StevenASchroeder@<wbr>...&gt; wrote:<br>
&gt;<br>
&gt; Is it correct that I only need to initialize the SRAM ECC after a<br>
&gt; power-on reset?  That is, if SIU_RSR[PORS] is zero I can skip the SRAM<br>
&gt; ECC initialization.<br>
&gt; <br>
&gt;  <br>
&gt; <br>
&gt; Thanks,<br>
&gt; <br>
&gt; Steve<br>
&gt; <br>
&gt; <br>
&gt; <br>
&gt; [Non-text portions of this message have been removed]<br>
&gt;<br>
<br>
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