no response from Kvaser after a long delay between messages

[LekasNet]

Describe the error

When using the Kvaser interface via python-can, the CAN bus can automatically stop transmitting received frames (bus.recv() returns None) after a long period of downtime, even if:

• The CAN bus is still physically active,
• ECU responses are present on the wire (externally verified),
• "bus.send()" continues to run successfully without errors,
• Kvaser driver statistics report status=ok and no bus shutdown status.

As a result, python-can reports false “no response” timeouts, while valid responses exist on the CAN bus.

This happens without causing an exception and does not require a forced reinitialization of the bus to recover.

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For playback

1. Use python-can with Kvaser leaf light v2 or Kvaser U100.

2. Open the CAN bus and connect to it in the normal mode (sending a request → receiving a response).

3. Leave the system in standby mode for a long time (about 1-5 minutes):

   • The application is running,
   • the tire is open,
   • The Kvaser is connected,

• The control unit is connected and turned on.

4. After the waiting period has expired, send a new CAN request.

Observed behavior:

• bus.send() completed successfully.
• bus.recv(timeout) returns the value None until the timeout expires.
• Python exception is not generated.
• External monitoring confirms that ECU responses are present on the bus.

The problem occurs periodically, but can be fixed after sufficient downtime.

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Expected behavior

bus.recv() must continue to return incoming CAN frames after periods of downtime until:

• the tire is open,
• The hardware is connected,
• The driver does not report a bus shutdown or a passive status with an error.

At a minimum, python-can must either:

• automatic recovery or
• returns a clear error indicating that the reception descriptor has become invalid.

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Additional context

This is apparently due to ** inactivity of the Kvaser receive descriptor or internal buffering behavior** after a long downtime.

Observed characteristics:

• Kvaser Driver Statistics Report ('canGetBusStatistics', `canReadStatus'):

  • status=ok

• "Bus load=0.0%"

• no overspending, no bus shutdown

• However, the function bus.recv() does not return any frames.

• Forced bus shutdown and reinitialization restore normal operation.

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Operating system and version:
Windows 10 / Windows 11 (x64) (tested on both)

Python version:
Python 3.9

python-can version:
4.5.0/4.6.1 (tested on both)

python-can interface/s:
kvaser

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Details

Feedback and logs

The Python feedback function does not start.

Example of a diagnostic log collected after the timeout:

[KvaserSnap:frame_write]
statistics=std_data: 0, std_remote: 0, ext_data: 0, ext_remote: 0,
err_frame: 0, bus loading: 0.0%, overspending: 0 status=ok

Additional note:

• bus.recv(timeout=0) returns the value "None" again
• An external CAN analyzer confirms that the ECU responses are simultaneously present on the bus