Difference between USB Serial in Windows and Linux

Question

I bought a Variense VMU931 inertial measurement unit (IMU) for a robotics project at school, and I am struggling to get it to reliably communicate with my laptop in Ubuntu. I am using C++ with termios to connect to it using 8n1 no parity blah blah blah. I've tried EVERY permutation of settings I can think of, and I still cannot reliably send commands to the IMU.

I called Variense support and spoke to the engineer that wrote their software, and he said it is a known issue. Evidently it works perfectly in Windows (and the Windows demo software worked fine with my device), but neither of us is aware of a significant difference between the USB Serial emulation in Windows and in Linux.

The constructor at the top of this file shows how I am opening and configuring the port:

https://github.com/jsford/FFAST/blob/master/VMU931/src/vmu.cpp

Any help would be great. I've been tearing my hair out over this! Thanks!

Answer 1

Use the cu utility for running tests with different parameters.

To debug the issue: run the USB packet capture with Wireshark on Linux directly and also on a Windows VM running in VirtualBox/VmWare. Compare the traffic.

Check which kernel module is chosen and loaded for that USB device. Use /sys/ filesystem for that: this virtual fs has information from kernel about what's used. Also, the lsmod -kind of commands show the kernel module usage. The driver choice for USB depends on something like <usb-manufacturer-id>:<usb-product-id> .

Put some printf s into the kernel module to see where is fails. Use the DKMS build system for rebuilding the kernel module. There is a config file somewhere in Linux to blacklist/whitelist the kernel modules - useful to make sure that the right one is loaded.

That's what I was doing to fix a driver of an USB-serial device.