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Re: Life of memory



At 09:09 PM 11/28/2000 +1000, Matt Donohoe wrote:

>I was looking at the amsat.org Separation pictures, then as I moved to the 
>bottom I noticed something a bit worrying.
>
>"Some of the images were corrupted in memory by radiation. Special thanks 
>to J. David Barrow, RiscOS programmer and JPEG innards expert, for 
>locating and flipping
>the single bit errors in those images, thus rendering them useful."
>
>Should we be concerned that at such a little amount of time after launch 
>there is already memory corruption due to radiation ?
>
>Just asking!

Not to worry.  The IHU-1, which is mission critical has RAD-hardened EDAC 
(error detection and correction) memory.  A "wash" routine checks this 
memory and repairs any bit errors.  If bit errors are found, the wash 
program updates the software error counter, and generates an "Event". .... 
.if you follow the telemetry, there has been one EDAC "hit" since launch 
(Event #9).  AO-13 used to have dozens a day near the end of it's life, 
with no ill effects at all.

The IHU-2, which is not mission critical, has two memory banks.  The 
primary memory bank which contains the functional program software is EDAC 
memory and can be "washed" for single bit error repairs, just as in the 
IHU-1.  There is also a large secondary memory bank (?8 megs) which is not 
EDAC memory.  The  images were stored in this area.  The "hits" were single 
bit flips, not at all unexpected.  This memory isn't used for critical 
functions, but can store large amounts of data.  The IHU-2 also contains 
Flash ROM which currently allows rapid rebooting of the IHU-2, if needed.

...hope this helps.


--
  ________________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
    Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
  ________________________________________________________________________

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