The reason it doesn't read from dupterm here is because the esp32 port (and esp8266) use os.dupterm_notify() instead, which forces a read of the dupterm sources from Python. Eg call that function when it's known that there is input to read.

Probably it should also read dupterm from mp_hal_stdin_rx_chr() as per this PR (and to be consistent with other ports), but it needs some thought as to the consequences of this change.

Ah. Thanks, that explains a lot.

This is a chicken/egg problem in my case.

I'm using the read (and ioctl+poll) methods of the object I'm hooking into dupterm to run the asyncio loop for a few milliseconds / until there's a character to be read. If asyncio doesn't run, the port doesn't get polled, nothing notices that there's data, thus nobody calls dupterm_notify. Oops.