Date: Sun, 2 May 1999 14:06:07 -0700
From: Russell E Owen
Subject: Re: 2.5m obslog 990501 (MJD 51300)
>When we tried and offset obj
>(.27, .11d) to one of the fiber positions, we started a run away in the ALT
>axis....
Large offsets send the MCP out of closed loop. This may be what
happened. Try to keep offsets to 0.03 degrees or less in any axis.
Having the axes halt (something you also observed) is more common
than a runaway here, but the MCP does seem fond of running away (not
to mention crashing and mishandling TCC commands).
>At some point during the offsets the telescope
>stopped tracking and the star  wandered off the fiber.  We were not able to
>get the star back because the TCC stopped responding to our commands.  We were
>not able to successfully issue an axis init (several were tried) and we got
>error messages when we tried axis stop, saying the command failed.  We were
>able to exit the TCC and issue a TELSTOP.
It is likely that the MCP hung and clogged up the port. That can
cause a TCC process to hang while trying to communicate with the MCP
-- though usually the TCC process should time out at some point. In
any case, only one process can talk to the MCP at a time, so if
tracking, say, is hung up while communicating, then you'll not be
able to issue an INIT from any other session. (I've thought about not
locking the port during the initial phases of an INIT, and it may be
a good idea, but it's going to have to be locked at some point.)
The safest thing to do when the MCP hangs is push a stop button and
go reboot the MCP. When the MCP comes back the TCC should start
working normally. You will have to do an AXIS INIT after things come
back (or any time you release the stop buttons).
Keep in mind that the MCP will slowly walk away (possibly at an
ever-accelerating rate) after you do an AXIS INIT.
-- Russell