epics-modules / labjack Goto Github PK

The LJTick-DAC register is write-only, so using a non-zero value for the pollMsec argument to drvModbusAsynConfigure results in the modbus exception 2:

# 2 additional analog outputs, setup to access LJTick-DAC occupying FIO0/FIO1
drvModbusAsynConfigure("LJT7_1_AO_2", "LJT7_1", 0, 16, 30000, 2, 8, 1, "LJT7_module")
2022/04/05 09:00:54.445 drvModbusAsyn::doModbusIO port LJT7_1_AO_2 Modbus exception=2

Changing pollMsec to zero eliminates the error.

There is interest on the part of APS in being able to use the LabJack with the Vibration Monitoring System (VMS) because the Measurement Computing E-1608 has more than 12 month leadtime.

This would require adding streaming support to the EPICS LabJack driver. I have read the documentation about that, and the vendor highly recommends using their high-level LJM library for streaming mode. Streaming mode is rather complex, using non-standard Modbus features, and would probably require changes to the EPICS Modbus support.

The LJM library is free, and is available for Linux (Centos 6.7 and later), Windows, and Mac. On Linux it supports Intel 32-bit, 64-bit, ARMv6, ARMv7l (armhf), and aarch64.

It seems that changing the EPICS LabJack module to use LJM rather than raw Modbus makes sense if we want to use the more advanced features.

The measComp drvMultiFunction.cpp driver could be used as the model and starting point, since the LabJack devices are very similar: analog in, analog out, digital I/O, waveform digitizer, and waveform generator.