Experimental Physics and
Industrial Control System

Hello,

I have a requirement for the motor record to have a mode in which it always immediately sends new demand positions down to the driver (always call move).

I believe at present the NTM behaviour does not include this capability.

I am looking for advice as to the best approach to adding this option in the motor record. Or even better, information on how to achieve this with the existing motor record.

See below for a detailed explanation of the requirement.

Many thanks,
   Giles.



I have implemented an extension to deferred moves in the type 3 driver for the Delta Tau Pmac. This new type of deferred move is coordinated so that all axes start and finish at the same time with the longest move determining the speed of all axes. This uses a pmac coordinate system and motion program to control the axes. It is used for the 6 circle diffractometer on I16, all 6 axes are in the same coordinate system - in a deferred coordinated move the driver passes parameters to the motion program giving the new position one or more axes, then executes the program.

The approach has been very successful except that occasionally the driver does not receive all of the demand positions that the client sends. In one instance this week, this resulted in a crash.

I am guessing this happens because the motor record does not always send a demand value when it sees an axis is moving. Consider the following steps


  1.  a previous move of axes kappa and kphi completes and causes a momentary adjustment in ktheta
  2.  ktheta is polled and its in position state is false, so its motor record DMOV is now false (and will be until the next poll in 1/10 seconds)
  3.  client sets PV -> driver mode = coordinated deferred
  4.  client sets new demand position on kappa
  5.  motor record calls move and the driver records the demanded position
  6.  client sets demand on ktheta
  7.  the new demand is for the same direction as ktheta is currently travelling and further than its current demand so NTM behaviour means that the driver is not called yet
  8.  client sets PV -> driver mode = GO
  9.  the driver sends the demanded positions and executes the motion program - but it has only seen kappa demand and ktheta does not move
  10. 1/10 sec after step 2 ktheta is polled and found to be in position - the demand will now be sent to the driver but all the axes are now under control of the motion program until kappa reaches its target.