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pyvisa / pyvisa-py

A pure python PyVISA backend
https://pyvisa-py.readthedocs.io
MIT License
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[COM] Cannot set flow_control to none for serial device Gwinstek PST3202 DC Power Supply #316

Closed mwcmwc12 closed 2 years ago

mwcmwc12 commented 2 years ago

Instrument details

Output of pyvisa-info

Machine Details: Platform ID: Linux-5.13.0-27-generic-x86_64-with-glibc2.29 Processor: x86_64

Python: Implementation: CPython Executable: /usr/bin/python3 Version: 3.8.10 Compiler: GCC 9.3.0 Bits: 64bit Build: Nov 26 2021 20:14:08 (#default) Unicode: UCS4

PyVISA Version: 1.11.3

Backends: ivi: Version: 1.11.3 (bundled with PyVISA) Binary library: Not found py: Version: 0.5.2 ASRL INSTR: Available via PySerial (3.5) USB INSTR: Available via PyUSB (1.2.1). Backend: libusb1 USB RAW: Available via PyUSB (1.2.1). Backend: libusb1 TCPIP INSTR: Available TCPIP SOCKET: Available GPIB INSTR: Please install linux-gpib (Linux) or gpib-ctypes (Windows, Linux) to use this resource type. Note that installing gpib-ctypes will give you access to a broader range of funcionality. No module named 'gpib'

Hi I am running into a weird issue with setting flow_control on this Power Supply. I am using pyvisa-py as the backend. run this simple code:

import pyvisa
from pyvisa.constants import ControlFlow
rm = pyvisa.ResourceManager('@py')
instr = rm.open_resource(
    'ASRL/dev/ttyUSB0::INSTR'
)
instr.flow_control = ControlFlow.none
print(instr.query("*IDN?"))

It throws this error: Traceback (most recent call last): File "simpleserialtest.py", line 7, in instr.flow_control = ControlFlow.none File "/home/xxx/.local/lib/python3.8/site-packages/pyvisa/attributes.py", line 184, in set instance.set_visa_attribute( File "/home/xxx/.local/lib/python3.8/site-packages/pyvisa/resources/resource.py", line 393, in set_visa_attribute return self.visalib.set_attribute(self.session, name, state) File "/home/xxx/.local/lib/python3.8/site-packages/pyvisa_py/highlevel.py", line 658, in set_attribute return self.handle_return_value( File "/home/xxx/.local/lib/python3.8/site-packages/pyvisa/highlevel.py", line 251, in handle_return_value raise errors.VisaIOError(rv) pyvisa.errors.VisaIOError: VI_ERROR_NSUP_ATTR_STATE (-1073807330): The specified state of the attribute is not valid, or is not supported as defined by the object.

However, if I set it to xon_xoff (which the instrument doesn't support) no errors occur. I have tried to separately connect to the instrument using Putty with flow control set to none and it works.

Any suggestions?

MatthieuDartiailh commented 2 years ago

This looks like a bug in pyvisa-py. I will transfer the issue and try to have a look ASAP.

MatthieuDartiailh commented 2 years ago

The offending line is at https://github.com/pyvisa/pyvisa-py/blob/main/pyvisa_py/serial.py#L421

0 should be considered a valid value. Care to make a PR ?

MatthieuDartiailh commented 2 years ago

Also pyvisa should use an IntFlag in place of an Ingenue for this attribute. I never got the chance to fix it and I cannot easily test changes affecting serial resources so if you want to have a look feel free to do so.

mwcmwc12 commented 2 years ago

Sure, I will go ahead and make the changes. Just curious, without looking into it too deeply, why is flow_control's setting not as straight forward as some of the other attributes like parity where parity is just assigns the enum, while flow_control has a bitwise operation AND before the assignment.

MatthieuDartiailh commented 2 years ago

Because the VISA standard says it is actually possible to set multiple ones at the same time and hence behave like a flag. I do not have the VISA reference handy but on can easily find it on the IVI foundation website.

mwcmwc12 commented 2 years ago

Learn something new everyday. Didn't realize you can even mix flow control since I personally never ran into an instrument that had that kind of specification. Thanks for the explanation.

Let me do a quick check in the lab on Monday with these changes and I will issue a PR if things go well.

MatthieuDartiailh commented 2 years ago

Sounds good.

MatthieuDartiailh commented 2 years ago

If you have the time you can also change IntEnum to IntFlag at https://github.com/pyvisa/pyvisa/blob/main/pyvisa/constants.py#L1080. It should be trivial but having somebody test it is always nice.