[Bug 321] ftdi_eeprom often fails silently

bugzilla-daemon at bugzilla.openmoko.org bugzilla-daemon at bugzilla.openmoko.org
Fri Mar 30 03:43:38 CEST 2007


------- Additional Comments From werner at openmoko.org  2007-03-30 03:43 -------
I'm now automatically cycling upstream VBUS in order to exercise the
board initialization. Unfortunately, the board now consistently uses the
default settings :-(

During my testing, I observed that VCC5 doesn't look good. There is
a typical cycle if I limit the current drawn from upstream VBUS to about
50-200 mA:


CH1 is VCC5 (= VBUS from upstream), CH2 is CS of the AT93C56A
(I often also only get the first burst on CH2, and it stays low
during the anomaly, so don't pay too much attention to CH2.)
That spike around -500 ms from the center looks a bit disturbing.
This is what it looks like magnified:


I've not been able to correlate this to any signal changing at
exactly the same time. However, LED7 begins its long blink about
7-8 ms before VCC5 collapses, and several other signals change
around that time as well.

If I allow a larger current, VCC5 doesn't break down as much, but
still shows a disturbance. So my suspicion is that something is
briefly causing a short, which then upsets the system.

I think this needs looking at by the hardware group.

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