[Python] python-can Notifier with PCAN-USB drops frames, causing UDS (udsoncan/isotp) requests...

I’m trying to run UDS over CAN using python-can, isotp, and udsoncan with a PCAN-USB interface. When I add a Notifier to log traffic to a BLF file, most of my UDS requests time out, even though the ECU responds (verified in an external CAN trace). Without the Notifier, everything works consistently.

Expected behavior


UDS requests (for example, tester_present) should succeed whether or not I use Notifier for BLF logging.

Actual behavior

• 
  With Notifier: ~90% of requests time out.
  
  
• 
  Without Notifier: all requests succeed.
  
  
• 
  External CAN trace shows ECU always responds promptly → frames are sent but not delivered through Notifier to the UDS client.
  

What I’ve tried

• 
  Adjusted udsoncan request timeout and Notifier timeout
  
  
• 
  Verified PCAN channel, bitrate, and filters
  
  
• 
  Tried BufferedReader, AsyncBufferedReader, and a custom polling loop → same issue
  
  
• 
  Manually polling with bus.recv() works consistently
  

import can
import isotp
import udsoncan
from udsoncan.connections import PythonIsoTpConnection
from udsoncan.client import Client
from udsoncan.exceptions import TimeoutException
from udsoncan.configs import default_client_config

bus = can.interface.Bus(
bustype="pcan",
channel="PCAN_USBBUS1",
bitrate=500000
)

isotp_params = {
'stmin': 5,
'blocksize': 40,
'wftmax': 0,
'tx_data_length': 8,
'tx_padding': 0x55,
'rx_flowcontrol_timeout': 5000,
'rx_consecutive_frame_timeout': 1000,
'max_frame_size': 4095,
'can_fd': False
}

addr = isotp.Address(isotp.AddressingMode.Normal_11bits, txid=0x7E0, rxid=0x7E8)
stack = isotp.CanStack(bus=bus, address=addr, error_handler=None, params=isotp_params)

final_filename = "log_file.blf"
logger = can.BLFWriter(final_filename)
notifier = can.Notifier(bus, [logger])

conn = PythonIsoTpConnection(stack)
with Client(conn, request_timeout=2, config=default_client_config) as client:
try:
response = client.tester_present() # 3E 00
print("Response:", response)
except TimeoutException:
print("UDS request timed out!")

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