How to reverse engineer a USB controller and read raw serial data in Linux

Question

I have a generic USB controller from a Brazilian brand based on a Chinese layout (Shanwan) that, despite installing the driver that comes with the Retropie and correctly configuring the digital inputs, does not correctly map all axis of the analog sticks.

I would like to use this opportunity to learn more about device debug, USB driver creation and reverse engineering USB devices to contribute to the open source community in that matter.

I want to know which Linux tools, references and documentation can describe this process of making a custom driver and allow the reading of raw USB serial data to remap this raw outputs to a retropie-friendly output.

Answer 1

What you need to do if you want to learn about USB on a low level is read up on USB drivers in LDD3 and carefully study /drivers/usb/usb-skeleton.c in the Linux repository. You should also have a good idea about how the USB protocol is specified. USB in a Nutshell is a good place to start.

You can use dmesg to see the specifics of the USB controller from the kernel's perspective. You can then modify the usb-skeleton to handle that specific device. From there you will need to probe the endpoints of the device, and initially preferably map them to nodes in the /dev-system. Once that is done, you can use a user land program to read and write to the endpoints, trying to figure out exactly what they do. From that information you can then write a HID driver that interfaces your USB device.