Check-motor-registers, cmr

At various places the OmsVme58 Tango server ensures the validity of the step position by comparing the internal (software) values and the controller registers. If the internal and controller registers deviate, the following sequence of conditions are tested:

• If the controller is 0 and within the step limits, the controller is loaded with the internal value, assuming that there was a power cycle.

• If the controller is non-zero but deviates from the internal value by shift-right-by-3bits, the internal value is loaded to the controller. This is a workaround for the hardware bug that the position registers are changed by the first homing after re-powering VME.

• If the controller is non-zero and inside limits, the internal value is overwritten by the controller value. We trust the controllers because they should keep track of the motor position.

• Otherwise the disagreement is not resolved automatically.

  We arrive here because the controller register and the internal value disagree and the controller register is outside the limits. How can this happen? Maybe beause of electronical noise or some other application operated the motor independent of Tango.

  • If the motor position is somehow known, write it down. You are safe. After you resolved the register discrepancies, see below, you can calibrate the motor, if necessary.

    If the position is not known, you may inspect the files in the directory /online_dir/MotorLogs. You may also inspect the versions of /online_dir/ipython_log.py (or /online_dir/motor_positions.bck, online.log)

  • Write down the attributes StepPositionController and StepPositionInternal.

  • Inspect the Tango server log file: /var/tmp/ds.log/OmsVme58_<instance>.log, e.g. by:

    $ tail -100 /var/tmp/ds.log/OmsVme58_<instance>.log
    

    or use Astor to inspect the stderr of the OmvVme58 server.

    Search for the last entry of this kind:

    OmsVme58::check_motor_register: Mon Sep  4 12:28:13 2017 
    OmsVme58::check_motor_register: p99/motor/d1.65, controller -100001 != internal -100000 and controller outside limits
    OmsVme58::check_motor_register: p99/motor/d1.65, controller -100001, limits [-100000, 100000]
    OmsVme58::check_motor_register: p99/motor/d1.65, the controller-is-right position is -0.500005 [-0.5, 0.5] 
    OmsVme58::check_motor_register: p99/motor/d1.65, the internal-is-right position is -0.5 [-0.5, 0.5] 
    OmsVme58::check_motor_register: p99/motor/d1.65, see HW manual
    

  • Depending on your decision, whether the controller or the internal value is correct, you have to set the StepPositionController or StepPositionInternal attribute.

  • Check the limits. If you trusted the controller, you have to change the limits.