RISC OS 5.30 on a new card

TL;DR backup your CMOS, cmdline/txt and config/txt from !Boot.Loader

I finally got around to upgrading from 5.28 to 5.30 on my Pi 4B. On trying to write to the SD card I found it had become read only. It’s only used for the DOS partition to load RISC OS ‘kernel’, as the CMOS is set to boot from my SSD on SCSIFS, but it was an old 8GB one previously heavily used in a Linux Pi and took that opportunity to fail. I remembered to take a copy of the CMOS file from the card and then binned it. I found another old 8GB SD card, burnt the 5.30 disk image on it, and copied in the CMOS file.

I was surprised when 5.30 booted in a low res welcome screen and left me in a 640×480 desktop. I tried changing the monitor definition file, but the maximum resolution was 1920×1080 rather my usual 2560×1440. That resolution wasn’t available in any of the other MDFs either. Then I remembered I might have had some settings in config.txt and cmdline.txt, so got the SD card out of the bin and had a look. cmdline.txt had disable_mode_changes and config.txt had quite a few settings including defining the 2560×1440 mode and raising the hdmi_pixel_freq_limit to allow it to be used. After putting those on the card, 5.30 booted correctly.

So if you are making up a new RISC OS image, remember to copy those three files from your hold one, to prevent lots of head scratching.