Subject: Re: [sloan-25mlog 4948] 2.5m obslog 20200205 (SJD 58885)
From: John Downey
Date: Thu, 6 Feb 2020 12:32:37 -0700
Jeff and I managed to duplicate the problems from yesterday's remote =
checkout.
As I suspected, the problem started when a tcc track 121,30 mount was =
commanded with a stop button in and the telescope not quite at 30 ALT.  =
We duplicated the problem with v1.10-6 today by putting the telescope at =
28 ALT and putting in a stop button, then trying a tcc track 121,30 =
mount - as expected it crashed the tmtcc_alt process which also hung the =
SDSSDC semaphore.  Jeff has fixed the tmtcc code to not crash when a =
requested slew cannot happen, but it will still loop the reposition =
errors until you do a tcc axis stop.
This problem was not seen during Monday or Tuesday checkout, probably =
because the telescope was close to 30 degrees ALT those days when the =
tcc track 121,30 mount slew was commanded.  This was a good bug to =
catch, because I suspect usually the conditions would not be right to =
cause it - we might have had it from the outset and only just now =
triggered the problem.
The TCC appears to be executing correctly, so presumably one could still =
do a tcc track 121,30 mount to get the mirror numbers even if the =
telescope is not at 30 and a stop is in.  One would just have to =
understand why they are getting a reposition error from the MCP every =
few seconds and do a tcc axis stop when finished.  In general, however, =
I believe that we should avoid this in the future.  =46rom what I =
understand of the process, commanding the tcc to track simply ensures =
that collimate is running - why not enable collimate without a track =
command?  Or if we want to do it with a track command, axes should be =
live and the telescope should move to exactly 30 and hold there while =
getting the mirror numbers.
Jeff and I both suspect that this reposition error bug is probably the =
old out of closed loop bug - we may have to modify things like the =
procedure for recording mirror numbers if we want these bugs fixed =
correctly.=