03 UART1 garbled output, solved

[kruthers64]

(Just in case anyone else tries this in 2025 or later and bangs their head for days against garbled output from the mini UART...)

I'm trying this tutorial on a Raspberry Pi 3b revision 1.2 board. I got stuck on tutorial "03 - UART1" because I could only get garbled output instead of "Hello World" over the serial interface.

Very long story short, I'm using current firmware and at some point Raspberry Pi changed the default core clock on boot, which changes the base value used for calculating baud rate. One fix is to force the core clock to 250 MHz by creating config.txt and adding the following line:

core_freq=250