DevGuide/USB-Serial
USB serial telemetry
Application
Until now you will need an external FTDI cable/chip or a pair of modems if you want to test and debug a Paparazzi system in your lab. This serial USB removes the need for this. It is possible to get telemetry through the same USB interface that you use for download. This USB serial might also be used to connect to an on-board payload processor (e.g. BeagleBoard).
Usage
The PCLK is increased to 30MHz (at least 18MHz, thanks for the info, Andre) to make the USB work properly. It is connected instead of Uart0 or Uart1 and uses the transparent PPRZ format. Just replace your telemetry with:
<subsystem name="telemetry" type="transparent_usb"/>
The USB serial will connect as a modem through /dev/ttyACM0 on a Linux system. Use this as device for the Paparazzi link application. The baudrate can be set to any value as it is fully virtual.
sw/ground_segment/tmtc/link -d /dev/ttyACM0