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SeeedBus: Crash occsionally. #2024
Description
Describe the bug
python-can crashes rarely with the error:
msg = self.bus.recv(0.0)
File "/nix/store/0amvifzhc5sv3p1b29dzwxd53njs74z3-python3.13-python-can-4.6.1/lib/python3.13/site-packages/can/bus.py", line 121, in recv
msg, already_filtered = self._recv_internal(timeout=time_left)
~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
File "/nix/store/0amvifzhc5sv3p1b29dzwxd53njs74z3-python3.13-python-can-4.6.1/lib/python3.13/site-packages/can/interfaces/seeedstudio/seeedstudio.py", line 279, in _recv_internal
end_packet = ord(self.ser.read())
TypeError: ord() expected a character, but string of length 0 found
To Reproduce
Use a while true loop to open the device quickly.
For my use-case, I needed to implement a flush_rx_buffer() function on user-level:
Please ignore my comments in the code, they may be outdated.
def flush_rx_buffer(self):
"""Discarding the received buffer."""
# As python-can does not implement any discarding of old messages, see:
# https://github.com/hardbyte/python-can/issues/1721
# The recv(0.0) is probably a non-blocking function, see:
# https://python-can.readthedocs.io/en/3.3.2/interfaces/socketcan.html
# That non-blocking function should return immediately.
while True:
msg = self.bus.recv(0.0)
if msg is None:
return
Expected behavior
Instead of a TypeError I expected to receive a None.
Additional context
OS and version: NixOS
Python version: 3.13
python-can version: 4.6.1
python-can interface/s (if applicable): seeedstudio
I'm using an asus nuc 15, so quite a fast CPU. I don't remember this error to appear on the slow raspberry pi pico.
Traceback and logs
def func():
return "hello, world!"
Activity
LucienDufour commentedon May 26, 2026
After some investigation I realized that the incoming usb-packets are not "frame-synchronized" (I also see no way to do this in hardware) with the usb-serial converter, so the data is split at arbitrarily positions. A software fix is needed.
The best way to handle this framing issue would probably be a ringbuffer that collects all the new incoming bytes, then processes them as soon as they are correctly processable.
Luz commentedon Jun 3, 2026
In case anyone is interested, I wrote a POC, which works perfectly for my use-cases:
https://github.com/Luz/seeedcan
Would be nice though, if the idea of "the serial buffer and the independent parsing" could be taken over and integrated to python-can.