The gs_usb interface support

[jxltom]

The gs_usb is the interface for Geschwister Schneider USB/CAN devices and bytewerk.org candleLight USB CAN devices such as candlelight, canable, cantact, etc. Refer to https://github.com/torvalds/linux/blob/master/drivers/net/can/usb/gs_usb.c and https://github.com/candle-usb/candleLight_fw

This PR implements the general driver for gs_usb devices based on pyusb, tested on Windows/Linux/Mac.

It looks like one of the gs_usb device cantact is supported in #853. However, that interface might diverge from gs_usb since it is going to add CAN FD support. This PR is more universal for gs_usb devices. Since this interface is using pyusb as backend, it has better crossplatform compatibility.

[codecov]

Codecov Report

Merging #905 (17f05d7) into develop (72c4ac9) will decrease coverage by 0.42%.
The diff coverage is 4.44%.

@@             Coverage Diff             @@
##           develop     #905      +/-   ##
===========================================
- Coverage    70.76%   70.34%   -0.43%     
===========================================
  Files           71       72       +1     
  Lines         7061     7106      +45     
===========================================
+ Hits          4997     4999       +2     
- Misses        2064     2107      +43     

[hardbyte]

Overall looks very clean, just minor comments mostly around documentation.

Bit of a shame to not have support for periodic messages or filtering.

[hardbyte]

@ericevenchick any chance you could provide your thoughts?

[ericevenchick]

@jxltom is right, CANtact is diverging a bit from gs_usb to add FD support. There's already a gs_usb_fd Linux kernel module for this: https://github.com/linklayer/gs_usb_fd

The goal was to keep support with the original gs_usb, but that's not my standard to modify. The gs_usb_fd module supports normal gs_usb devices, and FD devices provide a flag to show they have support.

[jxltom]

Hey @hardbyte thanks for your time for reviewing. I've already updated the PR according to the comments. Just let me know if there are more concerns. Thanks!

[hardbyte]

Thanks for making all those changes this looks good to merge.