Allow specifying unused MCS2 channels

[frankdeath]

If there is an unused channel between used channels (channel 0 and 2 are connected to stages and channel 1 is not), it causes timeouts when querying the readback position of the unused channel. This can give the appearance that the driver is taking much longer to poll than the specified idle polling period.

One possible workaround for this problem is to add a way for the used/unused axes to be specified from the iocsh and then make the getAxis methods in the only return an axis pointer for used channels.

[jwlodek]

Ran into this recently where sensors were connected to channels 3-5, but not 0-2, and there was a large delay in response due to the timeouts. Was going to make a PR that allowed for specifying the "first" axis that was connected, but I think as you say being able to have more granular control it would be better.

[Huijuan-Xu]

This issue was found long time ago and codes were added to support the feature. You can find comments in "Pull requests: Add MCS2CreateAxis and Cal/Ref/MCL frequency readback". The request seems not approved.

[kmpeters]

@Huijuan-Xu, the pull request was merged earlier this afternoon:

https://github.com/epics-motor/motorSmarAct/pull/8

I'm working on a new motorSmarAct (and motor) release.

[kmpeters]

An unusedMask argument was added to MCS2CreateController to allow unused axes to be specified:

https://github.com/epics-motor/motorSmarAct/blob/cdcfd093d4717cd96ff5f6183541870bf5e0c323/iocs/smarActIOC/iocBoot/iocSmarAct/smaractmcs2.iocsh#L8-L9

[kmpeters]

I don't have a smarAct controller to use for testing. It might be necessary to add a check for the unusedMask to getAxis:

https://github.com/epics-motor/motorSmarAct/blob/cdcfd093d4717cd96ff5f6183541870bf5e0c323/smarActApp/src/smarActMCS2MotorDriver.cpp#L195-L198

[MarkRivers]

Paul Fenter at ANL has a SmarAct system he brings to our beamline when he runs. You might be able to borrow that for testing.

[kmpeters]

It should not be necessary to check unusedMask in getAxis.

asynMotorController::getAxis returns pAxes_[axisNo]:

https://github.com/epics-modules/motor/blob/6ee5f4ebf44ddc46d989fc97b61d6dcc2c3bbc77/motorApp/MotorSrc/asynMotorController.cpp#L554

The asynMotorController constructor clears the memory it allocates for pAxes_:

https://github.com/epics-modules/motor/blob/6ee5f4ebf44ddc46d989fc97b61d6dcc2c3bbc77/motorApp/MotorSrc/asynMotorController.cpp#L139

The MCS2Controller constructor only creates an MCS2Axis object if the relevant bit of unusedMask is zero: https://github.com/epics-motor/motorSmarAct/blob/cdcfd093d4717cd96ff5f6183541870bf5e0c323/smarActApp/src/smarActMCS2MotorDriver.cpp#L88

The asynMotorAxis constructor is the only thing that sets an element of pAxes_ to a non-zero value: https://github.com/epics-modules/motor/blob/6ee5f4ebf44ddc46d989fc97b61d6dcc2c3bbc77/motorApp/MotorSrc/asynMotorAxis.cpp#L45

And the asynMotorPoller checks for a null pointer: https://github.com/epics-modules/motor/blob/6ee5f4ebf44ddc46d989fc97b61d6dcc2c3bbc77/motorApp/MotorSrc/asynMotorController.cpp#L651-L652

[kmpeters]

Fixed by #8