Add GPIB transport into QMI [Windows only]

[heevasti]

Description =========== Currently, the QMI transport layer does not have specific handling of a GPIB interface. Even though, not anymore commonly used, it is still present in some instrumentation like Tektronix's AWG 5014 model. And currently this interface is used for the AWG at the RT2 setup.

The GPIB device is usually a device that, when controlled through a PC, has an Ethernet, USB or similar interface to connect to the control PC. On some setups, USB/ethernet Prologix GPIB devices are used. The USB connector works on Linux, Mac and Windows and can use a VCP driver on Windows to 'serialize' the connection. Therefore, we can utilize these instruments with the regular serial/USB/tcp transport interfaces. On the contrary, the National Instrument's GPIB connector although having these and several more interfacing options, the USB connection cannot be used with the present transport implementations. The 'drawback' of the NI GPIB USB connector is that it needs the pyvisa package to be used with SCPI-protocol instruments and works only on Windows. The construction of the string to give to the pyvisa manager is not the same as for USBTMC instruments, which creates the incompatibility.

Proposed addition

When using NI GPIB USB connector on Windows, we need to be able to connect to it using pyvisa. For pyvisa we need to input for target device, which is a string. For this partuclar case, it is in the format "GPIB::X::INSTR" where X is a device number, e.g. 1. We need

• a transport parser class GpibTransportDescriptorParser in the transport.py

  GpibTransportDescriptorParser = TransportDescriptorParser(
  "gpib",
  [],
  {'devicenr': (int, True),
   'timeout': (int, False)})

• a transport_gpib_visa.py module that has main class QMI_VisaGpibTransport which inherits from QMI_Transport.
  • At constructor we want to have input devicenr: int and optional input timeout: int = 40000.
  • We need to override method _open_transport(self) with

    visa_resource = f"GPIB::{self.devicenr}::INSTR"
    rm = pyvisa.ResourceManager()
    self._device = rm.open_resource(visa_resource, timeout=self.timeout, write_termination='\n',
                            read_termination='\n')

  • On this will be added also a try-except and exception handling as appropriate.
  • property _safe_device and methods write and _read_message can most likely be included the same way they are included in transport_usbtmc_visa.py. It is not clear if the static method list_resources() is needed - evaluate while implementing the class.
  • close(self) method should also be in like in QMI_UsbTmcTransport class.
• On create_transport method in transport.py needs to be added handling for string format "gpib:devicenr[:timeout]". A new elif GpibTransportDescriptorParser.match_interface(...) is needed to return the correct transport class.

Affected components

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QMI

Modules to be created

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• qmi/core/transport_gpib_visa.py

Modules to be modified

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• qmi/core/transport.py

Tests to be created/updated

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• tests/core/test_transport.py
• tests/core/test_pyvisa_gpib_transport.py

Documentation to be updated

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• CHANGELOG.md
• Sphinx documentation
• QMI Confluence page

Hardware

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A Windows GPIB-connected instrument with NI's USB-GPIB device.