Wacky Racers on Glamo

Joerg Reisenweber joerg at openmoko.org
Tue Jul 29 19:43:56 CEST 2008

Am Di  29. Juli 2008 schrieb Andy Green:
> Hi folks -
> I made some progress reproducing and maybe even understanding the WSOD
> (White screen of Death) that the Glamo has always been partial to as
> part of a wider deathmatch with it.
> It seems that our choice about divider network (R1813 / R1814) to
> level-translate 3.3V CPU GPIO to 1.8V Glamo RST# might not have been the
> brightest thing we ever did.  I can reset the Glamo (provoking sticky
> WSOD) by touching Glamo RST# with my scope probe.  Glamo data says you
> need to assert RST# for 1us to get a reset, but it appears to reset the
> thing on any old glitch and is just recommending to hold it 1us to be
> sure everything got reset.
> With my scope probe applied, I cannot see any glitch: but it certainly
> knows if my probe is on since it resets immediately which is highly
> illegal behaviour for us.  So, there is a glitch and the energy needed
> for Glamo to accept it with our driving network is so low that that my
> scope probe capacitance dumping on it is enough, highly abnormal.
> I finally got put onto this when I found the Glamo registers are being
> forced back to reset values by resume time during some suspends here.
> (I noticed this because we hold a lot of unused Glamo engines in reset
> to avoid trouble, but the engines do not reset to being in reset, and
> they were all out of reset sometimes on resume)  Since we currently rely
> on bulk of Glamo regs staying where they were during suspend, this
> causes death.
> The Glamo docs also say that for 4ms after reset, we cannot touch the
> registers, and that matches a lot of the race outcomes I see, PLLs not
> started again sometimes even when we ran the correct code to start them,
> stuff passing PLL lock tests and then brain damage later when it updates
> cursor in framebuffer or brings up SD Card again.  The brain damage is
> very ugly to debug because one race outcome is the Glamo just jams nWAIT
> down forever if it isn't in a state to service your read [1].

Is this #''Openmoko Bug #1687: FR LCD goes blank suddenly''?
Do we need a hw-fix for this eventually?


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