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<== Date ==> <== Thread ==>

Subject: VMEbus ACFAIL* glitch causes OMS VME58 reboot
From: Ron Sluiter <[email protected]>
To: EPICS <[email protected]>
Date: Fri, 14 Jan 2011 09:13:42 -0600

We recently diagnosed an insidious problem here at the APS.
As with most really insidious problems, this one is caused by
a combination of errors.

We have a Tracewell System 22 VME crate with field swappable
power supply and fan tray that has been experiencing "Oms58_motor"
task crashes for over a year with increasing frequency.

After lots of board swapping, unplugging and plugging things in
and out, we finally determined that the Tracewell VME Power
Monitor is outputting ACFAIL* glitches (~ 7ns) on the VMEbus.

This, combined with the fact that the OMS VME58 board
processes the ACFAIL* line unfiltered, resulted in the VME58
board intermittently rebooting, which in turn caused a VME bus
error, which in turn caused the "Oms58_motor" task to crash.
(Note that the OMS MAXv does not monitor the ACFAIL* signal;
so this problem cannot happen with a MAXv.)

Lesson learned; if you have intermittent VME bus errors on the
memory address of an OMS VME58 board, and board swapping
does not resolve the problem, then check the ACFAIL* signal for
glitches.

Hoping this saves someone days of frustration,
Ron


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