can't make it work on tang nano 9k

[svofski]

Hi! I'm trying to make a demo work on my board, so far I only have very limited success.

I'm using Tang Nano 9K with pins 25, 26 set up with builtin pull down and 22 ohm series resistors. Then there's a USB-C breakout board and an OTG adapter. I monitor the output on the serial console and observe error LED.

1. When unplugged, error LED is blinking at approx. 1Hz
2. When I plug a keyboard, mouse or a gamepad, blinking stops, the error LED switches off.
3. The console doesn't display anything.

I tried attaching GAO to see if the system is alive. There definitely is some activity when a device is plugged or after reset. However I can't ever get anything to actually be reported and the devices also remain in uninitialized state (powered up, but status leds blinking etc).

It's worth noting that I had to swap DM and DP lines. When they are unswapped, there's no action that I can detect at all. I verified that the connections are fine from the board all the way to the pins inside of the USB receptacle. On a basic test project I could verify that the pins work for both input and output.

Devices that I tried: 8bitdo SN30pro (with all variants of X/Y/A/B on powering up), a no-name radio dongle mouse, a no-name radio-dongle keyboard, an Aula Aegis USB keybard.

I'm perplexed because there's not a lot that could go wrong in this setup. Do you have any ideas what I could try to debug this?

Here's a capture shortly after reset or replugging a keyboard dongle:

The trigger is a falling edge of usb_dp. It doesn't ever trigger again unless I replug the dongle.