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

Subject: OMS steppermotor problem
From: Albert Grippo <[email protected]>
To: [email protected]
Date: Fri, 22 May 1998 11:55:58 EDT
  At Jefferson Lab there are several MVME 167/177 IOCs with OMS VME44 
stepper motor control cards. When they are combined with an MVME 162 
card running HiDEOS in the same crate, we have been experiencing ioc 
crashes.  These may occur after several motor moves, or they may never 
occur, depending on the particular combination of software applications,
OMS card and stepper motor chassis, the latter being used to supply 
power to the motor and to microstep.  When the ioc crashes, it locks 
up immediately after a step is given, and there is no way to log on to 
determine the problem. 

  A great deal of time has been spent trying to debug this annoying 
problem.  The following is a summary of findings:

	1. The problem did not occur on a test ioc when there were 
	no other applications present. However, when an IP Digital48 
	I/O card was added along with an application which used scan 
	tasks on this card, we got consistent crashes (no crashes when 
	the scans were changed to passive).  We had been using the epics
	steppermotor record, but for debug purposes switched to a very 
	short subroutine record which talked directly to the OMS card. 
	This appeared to very consistently eliminate the problem, so 
	we thought there was a bug in the steppermotor record.

	2. When we moved the working applications to an operational ioc, 
	the problem resurrected, even with the simple direct OMS card 
	addressing subroutine. It occurred with or without the 
	steppermotors connected to the chassis, which ruled out the 
	motor itself.  In contrast, similar setups on 2 nearby operational 
	iocs, using epics steppermotor records, along with Digital48 
	scan task applications work extremely reliably. When questioned, 
	the developer of these systems said she spent many weeks working 
	with the hardware people to find the right combination of chassis 
	and OMS cards that worked.

	3. Further testing of the non-reliable system on the operational 
	ioc showed that the system could be made to work fairly reliably 
	by setting ECHO OFF.  The default option is ECHO ON and this is 
	set in the steppermotor record.  When it was set OFF in the 
	subroutine record version, 4 of the 5 motors appeared to work 
	reliably, and have been so operating for several months.  Setting 
	ECHO OFF appears to reduce bus traffic and hence the probability 
	of conflict with HiDEOS tasks and/or the fair amount of noise 
	which was present on the bus.  However, the fifth motor continued
	to cause crashes after a random number(generally 1- 20) of steps 
	were given.  This problem was greatly and consistently reduced 
	by removing an application on the ioc which used GPIB 1 second scan 
	tasks.  Removing another GPIB application on the ioc with only 
	passive scans made no difference. The system is now running with
	only the Digital48 and passive GPIB tasks, but still crashes on
	occasion, after perhaps several hundred steps.  We are int he process
	of removing all HiDEOS tasks from this ioc.

	4. Another system, developed independently by a third person at 
	the lab, and using the epics steppermotor record, also experienced 
	periodic crashes when running on an operational ioc with other 
	applications, several of which used HiDEOS.  When this system was 
	moved to a spare ioc with no other applications, the crashes ceased.

 Has anyone else experienced such problems with the OMS VM44 ?



 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
    Al Grippo
    Jefferson Laboratory
    Newport News, VA
    757-269-5015
 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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