USB Tx buffer overflow undetected

[Nakakiyo092]

Description of the bug

CANable fails to detect a USB transmit buffer overflow most of the time. Message is lost without error.

To reproduce

I made a script to produce a buffer overflow, which is provided at the end of this post. It sends 200 V commands at once then checks the reply. I got only 154 replies and one of them was corrupted as follows:

...
b158aa7 github.com/normaldotcom/canable2-fw[CR]
b158aa7 github.com/normaldotcom/canable2-fw[CR]
ldotcom/canable2-fw[CR]
b158aa7 github.com/normaldotcom/canable2-fw[CR]
b158aa7 github.com/normaldotcom/canable2-fw[CR]
...

It is obvious some of data was lost. However the result of E command showed no error.

CANable Error Register: 0

Expected behavior

Buffer overflow in this case is quite normal, but CANable should detect it and notify of the error.

Script to produce buffer overflow

overflow.py

import time
import serial

# connect to canable
# device name should be changed
canable = serial.Serial('/dev/ttyACM0', timeout=1)

# send a lot of command without receiving data
# maybe 200 is not enough depending on environment
for idx in range(0, 200):
    canable.write('V\r'.encode())

# recieve all reply
rx_data = b''
while True:
    time.sleep(1)
    tmp = canable.read_all()
    rx_data = rx_data + tmp
    if len(tmp) == 0:
        break

# print reply
rx_data = rx_data.replace('\r'.encode(), '[CR]\n'.encode())
print(rx_data.decode())

# check error
canable.write('E\r'.encode())
time.sleep(1)
print(canable.read_all().decode())

canable.close()

My environment:

Ubuntu 24.04.1 LTS
Python 3.12.3
pyserial 3.5

[Elmue]

This will not happen anymore with the new Slcan 2.5 firmware https://netcult.ch/elmue/CANable%20Firmware%20Update