This is python-usbtmc, a user-space Python module that uses libusb to communicate with USBTMC-capable devices. It works in Linux, MacOS, and Windows.
It aims to be an improvement relative to the older USBTMC support implemented as part of the Python-IVI project, as found here:
https://github.com/python-ivi/python-usbtmc
This older module has several shortcomings, the most important one being that it seems to be no longer actively maintained. Other than that, it has been very useful to us, both in the lab (with a few patches here and there), and as a reference while developing our own usbtmc driver.
USBTMC is a protocol specification for controlling test- and measurement equipment over USB. It is a so-called "USB class". Its specification can can be found at the USB Implementers Forum (USB-IF).
[1] USB 2.0 specification [2] USBTMC_1_00.pdf (40 pages) [3] USBTMC_usb488_subclass_1_00.pdf (30 pages) [4] SCPI specification [5] IEC 60488.1 specification [6] IEC 60488.2 specification
Documents [2] and [3] can be downloaded from https://www.usb.org/sites/default/files/USBTMC_1_006a.zip.
Written in Python.
Depends on the libusb-1.0 library to perform control- and bulk USB transfers as defined by the USBTMC standard.
In Windows things are more complicated than they could be.
- Libusb dependency
- WinUSB
- Registering a driver for your device. Use the "Zadig" program to bind your device to the WinUSB driver.
Supporting USBTMC on test- and measurement devices turns out to be not quite trivial. Many devices out there claim to support USBTMC, but often they show behavior that is not in full compliance with the specification.
This is especially true for lower-cost brands, but unfortunately even high-end devices often shows such non-standard behavior.
This is unfortunately true to an extent that I would recommend not using USBTMC if you can avoid it. If your device supports Ethernet, and you just want to control it using SCPI commands, you're usually much better off just opening a TCP socket to port 5025 (the standard TCP port most modern lab devices implement for SCPI access) and use that.
However, some devices don't have an Ethernet port; and on some devices the USBTMC performance is (surprisingly) better than what can be achieved over TCP. As an example, I have a Keysight 33622A waveform generator that I can upload arbitrary waveforms to. Using USBTMC I can do that at a pretty dismal data rate of about 1.8 MB/s, but using Ethernet is somehow even worse, at 1.0 MB/sec.
Anyway, about those quirks:
This package was tested against any USBTMC devices that I could get my hands on; see the example programs under source/usbtmc_tests/devices/ for the current list.
In the process, I uncovered a bunch of quirky behaviors where devices don't follow the standard to the letter.
Wherever possible, I have tried to come up with a more-or-less generic workaround for the quirky behavior, which overrides the default behavior. The known behavioral quirks are collected, for each type of device, in the "usbtmc_interface_behavior.py" source file. Whenever a device is opened this 'quirks database' is probed to find a corresponding set of behavior hacks. This mechanism allows us to work around many quirks. Unfortunately, this only works for devices I have been able to test.