I used to read the page https://ardupilot.org/dev/docs/raspberry-pi-via-mavlink.html to connect my RPI to FMU end December 2019.
Now that I look at the page the content of the page has been updated and several critical information disapearded.
An example: From https://www.researchgate.net/publication/323683430_Communicating_with_Raspberry_Pi_via_MAVLink you can read “On newer versions of Raspberry Pi 3 the uart serial connection may be disable by default. In order to enable serial connection on the Raspberry Pi edit /boot/config.txt and set enable_uart=1. the build-in serial port is /dev/ttyS0. Once MAVProxy has started you should be able to type in the following command to display the ARMING_CHECK parameters value”.
This used to be visible on the web last month but not anymore
Hope someone can help me to retrieve the December 2019 content