Getting to run SEL4 on a Raspberry Pi 3B

For a University project I am doing some experiments with SEL4 on a Raspberry Pi 3B. I have followed the steps on this website to install SEL4 on the Raspberry Pi using UBoot:

After the installation I have some problems with reading the RS232 output from the booting process using Minicom on Ubuntu, I am using a baudrate of 115200 8N1, is this the correct setting? The only output I am seeing is some random characters. I am using this shield to connect a RS232 cable. My project supervisor suggested that it might be necessary to use a null modem to read the RS232 signal, is this the case for this project?

I was also thinking to just skip reading out the boot process and directly connect to the SEL4 OS. Is this a possibility, and can I do this by connecting a monitor to the Raspberry Pi, or do I need to log in to the OS using a usb or ethernet connection?

I hope there is someone who could help me with this and it would be fun to start doing my experiments using the SEL4 OS.

Thank you in advance,

Nick Moone
Student BSc Computer Science
University of Amsterdam
The Netherlands

115200 8N1 is correct. I don’t really see a reason why this would not work, docs says it exposes GPIO14(TXD) and GPIO15 (RXD). However, you might indeed need null modem cable crossing TX/RX. Does the UART shield work when you install Linux on the RasPi?

For practical reasons, there is no need to use RS232 nowadys, a simple USB/UART adapter with 3V logic levels (e.g. Adafruit CP2104 Friend - USB to Serial Converter : ID 3309 : $5.95 : Adafruit Industries, Unique & fun DIY electronics and kits or 1PCS Great IT CJMCU CP2102 MICRO USB to UART TTL Module 6Pin Serial Converter UART STC Replace FT232 NEW for Arduino|usb random|usb computerusb computer remote control - AliExpress) would be sufficient. Just connect the pins from 2x20 GPIO header directly. TX is pin 8, RX is pin 10 and GND is pin 6 (see As with the null modem cable, you need to cross RX and TX, ie. connect RX to TX and TX to RX on the USB/UART adapter.