[USB2_Soft / UART Loopback] Error in Communication Device Class (Abstract Control Model) / Zero length descriptor references

[Semnodime]

usb2_soft

usb_uart_loopback.gprj

dmesg ->

[  +0,000000] usb 1-4: new high-speed USB device number 1 using xhci_hcd
[  +0,156252] usb 1-4: New USB device found, idVendor=33aa, idProduct=0000, bcdDevice= 1.00
[  +0,000007] usb 1-4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[  +0,000002] usb 1-4: Product: USB2Serial
[  +0,000001] usb 1-4: Manufacturer: Gowinsemi
[  +0,000619] cdc_acm 1-4:1.0: Zero length descriptor references
[  +0,000004] cdc_acm: probe of 1-4:1.0 failed with error -22

[kyonmiriam]

Hi, I have understood your problem.
Sorry we haven't had time to test on Linux yet because we lack such a device.
But I guess this issue may be caused by a small bug in the USB descriptor. We can see such a line of error prompts in USBTreeView.

This corresponds to line 212 in the src/usb_descriptor.v file in the project. You can see that h02 is written here.

Maybe changing this to h00 and rebuilding the project will help.

[kyonmiriam]

After careful inspection, it was confirmed that there was an error in the USB interface descriptor related content in the previous demo.

The relevant content has now been corrected. The demo has been updated and additionally tested on Linux and macOS. You can try the updated demo.

As you can see, now Linux can recognize it normally as /dev/ttyACM0 . We tested on Ubuntu 22.04 and openSUSE tumbleweed, and the demo works fine.

@Semnodime