> mk: don't know how to make 'acm.h' in directory /sys/src/cmd/usb/serial
Sorry, I thought that was already in the distributed version. I've updated
the serial.tar file, so it should be complete now if you try again.
> And how do I read data (if possible, not through C)?
Set the baud rate with
echo b9600 >/dev/eiaU?/eiaUctl
and then you can receive data with
cat /dev/eiaU?/eiaU
or set up an interactive conversation, as Steve Simon suggested, with
con /dev/eiaU?/eiaU
More information is in the manual - uart(3), usb(4), con(3)