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? cheers jOERG
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