SLCAN problem with VSCOM USB-CAN Plus

Joakim1 · February 8, 2019, 10:42am

Hi,
I am trying to use the GUI tool with the “USB CAN Plus” dongle from VSCOM under Windows 10, but GUI tool does not get any ACK from the SLCAN driver when trying to set it up.

Has anyone used this combination, and has any idea what the problem is? Does the VSCOM dongle even support SLCAN in Windows (I can only find references to Linux in their documentation)?

regards,

Joakim

pavel.kirienko · February 8, 2019, 11:06am

There may be a problem on either end of the channel. There is no strict specification of the SLCAN tunneling protocol, so every implementer has to make their own assumptions, thus possibly disrupting cross-vendor compatibility. Consider connecting to your device via a simple serial line terminal emulation program (e.g. PuTTY works well on Windows) to investigate what is going wrong during the initialization sequence. The implementation of the SLCAN driver used in the GUI tool can be found in the Pyuavcan repo. The initialization part is specifically here:

github.com

UAVCAN/pyuavcan/blob/b757ead922171bb27bb8320f3d03e5fc4d9858a0/uavcan/driver/slcan.py#L415-L443


# Sending an empty command in order to reset the adapter's command parser, then discarding all output
send_command(b'')
try:
    wait_for_ack()
except DriverError:
    pass
time.sleep(0.1)
conn.flushInput()


# Making sure the channel is closed - some adapters may refuse to re-open if the channel is already open
send_command(b'C')
try:
    wait_for_ack()
except DriverError:
    pass


# Setting speed code
send_command(('S%d' % speed_code).encode())
conn.flush()
wait_for_ack()

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P.S. I personally found the hardware from VSCOM to misbehave frequently and to be generally unreliable, but it may have no relation to your current issues.