follow-up re system software

Wolfgang Spraul wolfgang at qi-hardware.com
Fri Nov 20 23:35:39 EST 2009


Lars,

> >> Is that issue considered a show stopper? until one understands if
> >> the root cause is hardware or software, one could argue it as
> >> being STOP SHIP severity.
>
> Just wanted to let you know that I identified the problem and fixed it :)
> 

Wow this is good! Makes my day...
Just yesterday I met with our manufacturer to speed up the road to production,
and I had Ron's reminder in the back of my mind and didn't feel that great.
But now that bug is also fixed so it's great.

Way to go!
Wolfgang

On Sat, Nov 21, 2009 at 04:37:30AM +0100, Lars-Peter Clausen wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Wolfgang Spraul wrote:
> > Ron,
> >
> >> Is that issue considered a show stopper? until one understands if
> >> the root cause is hardware or software, one could argue it as
> >> being STOP SHIP severity.
> >
> > No, not a show stopper. Almost the same hardware design as ours has
> > shipped over 60,000 units already. If there would be a serious
> > microSD problem it would have been found. What that means is that
> > there is at least a workaround to the problem. Also, I vaguely
> > recall that we have not seen this issue when we started to work
> > with the original 2.6.24.3 kernel, but only after we cleaned up the
> >  sources and up-leveled to 2.6.31. All hardware ships with bugs.
> > Many times you can even argue what is a hardware bug and what a
> > software bug. The lowest levels of software routinely have to
> > 'cover up' / 'workaround' hardware bugs, making the hardware look
> > 'stable' for higher levels of software.
> >
> > For this particular problem, I am confident enough that we will
> > find a software workaround in the end to not make it a STOP SHIP
> > severity. Otherwise we would never ship anything, and you would
> > happily use lots of other consumer electronics with bugs inside you
> > just don't know about.
> >
> > However, I am clearly aware of this bug, and hopefully we get to
> > the bottom of it soon... The beauty of open - everything is known
> > :-) Wolfgang
> Hi
> 
> Just wanted to let you know that I identified the problem and fixed it :)
> 
> Turned out to be, as I suspected, a caching issue. The MIPS
> architecture has two independent caches: One for instructions and one
> for data.
> If data is read from the sd card it goes into the data cache. If it
> hasn't been used in while it's probably going to be replaced by other
> data and the pages holding the sd card data are going to be flushed
> which means their contents is written to the main memory.
> Now if we want to boot from a sd card we are going to execute the data
> read from the card. But as said earlier MIPS has two different caches.
> So in our case the instruction cache is going to be filled from the
> main memory. But the data read from the sd card has not been flushed
> from the data cached yet and so we end up executing random leftover
> data. The solution is to flush the the data cache after reading from
> the sd.
> 
> - - Lars
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.9 (GNU/Linux)
> Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
> 
> iEYEARECAAYFAksHYHoACgkQBX4mSR26RiOcHACfWaY/4DO9MrkFqRo6++v5inc7
> 4YAAn2RVPbfBzRgSZ3uReByBI4I77YON
> =5Zck
> -----END PGP SIGNATURE-----
> 
> 
> _______________________________________________
> Qi Developer Mailing List
> Mail to list (members only): developer at lists.qi-hardware.com
> Subscribe or Unsubscribe: http://lists.qi-hardware.com/cgi-bin/mailman/listinfo/developer




More information about the discussion mailing list


interactive