Question about using profile moves (PVT) will a time pulse output

[MarkRivers]

I would like to start a PVT trajectory, and "simultaneously" start a periodic pulse output that will trigger my detectors. That way I know exactly where on the trajectory each detector image was collected. Ideally I would also like to capture the commanded motor position and the readback error at the same time that each trigger pulse is output. I realize I may not be able to guarantee perfect synchronization, but is the possible at all, and if so how can I do it?

[motorapp]

Let's work on this together.

The output compare function can be used to provide a pulse when the incremental encoder position matches predefined values. The output compare options can be found at the top of the trajectory screen. Output compare requires an incremental encoder and a servo motor.

Output compare (encoder position match) is implemented in hardware and has good timing specifications. The output pulse doesn't depend on the controller servo update period. The servo update period is 976us with TM at the default value of 1000.

Thinking out loud..
The commanded position and error are computed values and depend on the servo update period. Data record and record array data sources offer the best timing, providing updated values every 2nd servo period.

First idea.
The driver could be altered to initiate the record array command at profile start, capturing the required data. The driver user array function can be used to read the result, or the driver could be altered to read the result at profile completion. To obtain the commanded position and error at the pulse time, the correct time or array index is required. Scanning the array for positions that are closest to the predefined output compare positions would find the array indexes of interest. The record array function is limited by the controller memory.

Thoughts?

[MarkRivers]

@motorapp I know about the position compare option. However, it is not suited for my use case, which is general purpose:

• It does not work for open-loop steppers without encoders, which many of our axes are.
• In a complex motion no single axis may be moving all the time. Each may slow down a lot or even stop.

Thus, I want the option for a time-based trigger and position capture in close synchrony with that trigger.

[motorapp]

Apologies, I missed that a time-based output pulse is wanted (blind).

Time-based output pulse:
Could you indicate the desired output frequency and period? All I can think of is SB and CB commands combined with the servo update time period (2^n). I'll keep at it.

Position and error information capture
Recommend investigating if the following Galil features could meet the need.

1. Position capture. AL and RL commands. Capture through an opto isolated input has a 5us delay.
2. Record array. RA, RD and RC commands.

I couldn't see the captured position in the data record. The data record "user data" (ZA command) may be helpful.

[MarkRivers]

Could you indicate the desired output frequency and period?
Frequency 1 Hz - 1000 Hz. Pulse duration not too important, since triggers are edge sensitive.

I think I want to use the record array commands, since those can run at a user-specified frequency, which I would set to match the pulse output frequency.

Mark

[motorapp]

The record array and data record both update at 512Hz maximum, with TM set at default 1000. TM could be lowered to increase the frequency.

Regarding the periodic output pulse, I recommend contacting Galil for their help.

I don't think the below pseudo Galil code would be sufficient, due to timing issues.
Start Loop
SB1;WT ;CB1; WT
End Loop

I've been thinking a STM32H7 nucleo (400MHz + network + cheap) would be suitable for the perodic output pulse. Or another external programmable pulse generator. It could be paired with position capture and record array on the Galil.

[motorapp]

When evaluating the suitability of the Galil record array facility, the Galil EPICS driver's "user array" feature may be helpful.

On the "User Array" MEDM screen, a Galil microcode array name can be specified in the text entry field. Click the upload button to upload the array data to an EPICS waveform record.

[MarkRivers]

On the "User Array" MEDM screen, a Galil microcode array name can be specified in the text entry field. Click the upload button to upload the array data to an EPICS waveform record.

Thanks for that info.

I've been thinking a STM32H7 nucleo (400MHz + network + cheap) would be suitable for the perodic output pulse. Or another external programmable pulse generator. It could be paired with position capture and record array on the Galil.

Each of our stations already have programmable pulse generators. The question is how to synchronize the position capture with the external trigger?

[motorapp]

Connect the external pulse to the digital input required to capture the axis of interest when the pulse occurs. Input 1->Axis A, Input 2->Axis B, etc. The digital input delay is around 5us.

If a controller thread is required for custom code, I recommend aligning the spare axis with the spare thread. Axis A is thread 0, B is thread 1, etc.
The desired thread can be freed by commenting out the relevant GalilCreateAxis call in iocBoot/iocGalilTest/DMC01Configure.cmd lines 88-96. The driver will dump a file _gen.dmc in the iocBoot directory. The _gen.dmc file could be altered in a text editor to add the custom thread required. The updated code file can then be specified in GalilStartController.

User-defined records could be useful because they allow EPICS records to be attached to Galil micro-code variables; below is a description.

User-defined records can be defined in GalilTestApp/Db/galil_userdef_records.substitutions file. To add new variables, I recommend copy/paste the line that defines the "begin" variable and then renaming the variable to the required name. For example,
{0, "MYVAR", "myvar", "VAR", "I/O Intr", 0, 1, 0, 1, "MINOR", "MINOR", "Invalid", "Ok", "MAJOR", "NO_ALARM", "0", "", "YES"}

This will create associated PV's.
DMC01:MYVAR_SP - AO record, double precision float output. Floating point setpoint.
DMC01:MYVAR_MONITOR - AI record, double precision float input. Floating point readback.
DMC01:MYVAR_CMD - BO record, binary output. 0, 1
DMC01:MYVAR_STATUS - BI record, binary input.

These records are defined in GalilSup/Db/galil_userdef_records.template. Feel free to add new record types as required (eg. string).

Information communication
Driver->Controller
Write to the _SP or _CMD record, and the value will be written to the controller variable.

Controller->Driver
To send a value update from the controller to driver, use the following micro code
MG "myvar", myvar
The above line will cause an unsolicited message from the controller to the driver that contains the updated value of the myvar variable.
The custom PV will be updated with the new value.

The controller code can be traced by
camonitor -S DMC01:ERROR_MON (Unsolicited messages without a user-defined record are routed here)
Using the command console at the bottom of the DMC controller screen, tracing can be controlled by:
TR1 - Begin tracing
TR0 - Stop tracing