usb_cdc integration into uFork/uCode

[dalnefre]

As mentioned in this introductory post, we're hoping to integrate the usb_cdc module into the uFork/uCode microcode processor. We've taken an approach similar to the uf16 integration, combining the Verilog files into a usb_cdc library for integration into the uCode processor on the Fomu as a serial UART-USB bridge.

Unfortunately, the current integration fails to enumerate. I would assume that USB device enumeration could complete successfully without any USB-UART data flowing, as long as the pin configurations and clocks are provided correctly. We've tried to follow the example given in soc.v for the Fomu

We are primarily experienced in software development, so perhaps we've made a simple mistake that could be found with a quick code-review. We also don't have much in the way of tooling for hardware/firmware development, so it's difficult to observe the behavior of the device itself. Any help would be appreciated.

[ulixxe]

Hi Dale, a thing that has to be corrected is the "output" declaration of both usb_dp and usb_dn pins in cpu_top.v. They are "inout" as you can find in uf16soc.v (usb_p/usb_n).
I hope that solve the problem.

[dalnefre]

Thank you for this correction! These details are so easy to overlook.

I've changed D+ and D- to inout. Sadly, the USB device still does not enumerate. I will go back and compare your implementations to mine and try to find additional overlooked details.

[dalnefre]

Found and fixed inverted logic for reset signal. The USB-Serial bridge is now working and connected as console i/o for uFork/uCode. Thanks for your help!