Handling power failure - MPC5200

[VanBaren, Gerald (AGRE)]

> -----Original Message-----
> From: linuxppc-embedded-bounces at ozlabs.org
> [mailto:linuxppc-embedded-bounces at ozlabs.org] On Behalf Of
> Jón Benediktsson
> Sent: Friday, November 05, 2004 9:14 AM
> To: Wolfgang Denk
> Cc: linuxppc-embedded at ozlabs.org
> Subject: Re: Handling power failure - MPC5200
>
> > In message <OF368071C2.FBC6B7BC-ON00256F42.003F3DF3-00256F42.
> > 0044E8BB at marel.is> you wrote:
> > >
> > > Capacitors on the supply provide me with some
> milliseconds to repond
> to
> > > power failure, which I would
> > > like to use to do as much cleanup as possible before power is
> > > totally gone.  In particular, I am concerned
> >
> > How many is "some"? If it's not >100 or so it is probably 
> not  worht
> > the effort...
>
> With the current design "some" is <50, but we can change the
> design if we find it necessary.
> 
> >
> > Use the standard methods: use the CF card read-only  (many 
> CF  cards
> > can  be  damaged  [beyond  repair]  when  you power off
> while a write
> > operation is in progress).
>
> Is this an acknowledged fact by CF manufacturers or based on
> experiece ?
>
> Thank you very much for your input.
>
> Regards,
> Jón Benediktsson
> Marel hf.

Hi Jón,

Read the CF card detailed specifications carefully (and if it ain't in writing, it ain't real).

What I've seen is marketing bullet points saying the cards can survive a power loss event with no loss of data, but when I read the detailed CF specification, the disclaimer was that power had to be held up for X mSec (I forgot what X was, 2mSec or 10mSec most likely) after the last write operation.  The marketing bullet point was exactly that: marketing.  The real requirement levied on the user (you) was that you had to have X mSec power hold up after the last write operation (i.e. a X mSec power fail warning with no write operations after the PF warning).  The hold-up requirement gave the CF internals enough time to complete a flash write cycle.

gvb

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