[COM] usbtmc timeouts with SPD3303C

[mik1234mc]

Dear all,

We use Siglent SPD3303C over usbtmc connection (at debian11) and querying the device over pyvisa times out in most of the cases (only once I got an ID string). Device.write("XXX") works correctly. The issue must be in pyvisa because if I use the usbtmc driver directly, the queries work as expected.

versions:
pyvisa-py in ./.local/lib/python3.9/site-packages (0.5.3)
pyvisa>=1.12.0 in ./.local/lib/python3.9/site-packages (from pyvisa-py) (1.12.0)

query error with pyvisa:

import pyvisa
pyvisa.ResourceManager().list_resources()
('ASRL/dev/ttyS1::INSTR', 'ASRL/dev/ttyS0::INSTR', 'ASRL/dev/ttyUSB0::INSTR', 'USB0::1155::30016::SPD3EDCD3R1335::0::INSTR')
src =pyvisa.ResourceManager().open_resource("USB0::1155::30016::SPD3EDCD3R1335::0::INSTR")
src.query("*IDN?")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/michael/.local/lib/python3.9/site-packages/pyvisa/resources/messagebased.py", line 648, in query
    return self.read()
  File "/home/michael/.local/lib/python3.9/site-packages/pyvisa/resources/messagebased.py", line 486, in read
    message = self._read_raw().decode(enco)
  File "/home/michael/.local/lib/python3.9/site-packages/pyvisa/resources/messagebased.py", line 442, in _read_raw
    chunk, status = self.visalib.read(self.session, size)
  File "/home/michael/.local/lib/python3.9/site-packages/pyvisa_py/highlevel.py", line 519, in read
    return data, self.handle_return_value(session, status_code)
  File "/home/michael/.local/lib/python3.9/site-packages/pyvisa/highlevel.py", line 251, in handle_return_value
    raise errors.VisaIOError(rv)
pyvisa.errors.VisaIOError: VI_ERROR_TMO (-1073807339): Timeout expired before operation completed.

working queries without pyvisa:

>>> import os
>>> d = os.open('/dev/usbtmc0', os.O_RDWR)
>>> os.write(d, bytes('*IDN?\r\n', 'ascii'))
7
>>> os.read(d, 1024)
b'Siglent Technologies,SPD3303C,SPD3EDCD3R1335,1.02.01.01.03R2,V1.3\n'

Michael

[MatthieuDartiailh]

Hi, could you try to mimic your os calls by passing write_termination = "\r\n" and read_termination="\n" ?

My second question is are you sure your device uses USBTMC rather than serial over USB ? I am asking cause the os calls looks suspiciously simple for USB TMC.

[mik1234mc]

Unfortunately, no luck with any termination character combination. I received the ID string just once from about 10 attempts.

The device manual states USB TMC and I am opening /dev/usbtmc0 dev. The USB2serial would be registered as /dev/tty*, I guess.

[MatthieuDartiailh]

Can you have a look at the discussion in #256 (starting at this comment #256 (comment)) and see if this helps in your case. I do not have the hardware on hand to explore this issue.