Delete me: Installing RISC OS on the Raspberry Pi 4 (Rev #3)

Overview

This is the procedure to use if you want to run RISC OS 5.27 on the Pi 4B but need to construct the SD card image from Windows/macOS/Linux (i.e. you haven’t got another RISC OS machine).

Getting started

You will need the following items:

• A class 10 MicroSD card (8GB minimum).
• The “RISC OS Direct” image from https://www.riscosdev.com/direct/
• The Beta RPI ROM archive (BCM2835Dev.5.27.zip), available from the Downloads page.
• Up-to-date Raspberry Pi 4 firmware (start4.elf and fixup4.dat) from the GitHub page.

Preparing the SD card

• Unpack the RISC OS Direct archive and use a utility such as Win32DiskImager (Windows) or Etcher (Linux/macOS) to copy the image to the MicroSD card. This will create an SD card in a suitable format, but only the first 8GB of the card will be usable by RISC OS.

• The RISC OS Direct image has an old RISC OS ROM installed: this file must be removed before proceeding. Open the DOS partition on the SD card (this will usually be the only one accessible) and delete the file “RISCOS.IMG”. Do not delete any of the other files.

• Unpack the BCM2835Dev.5.27.zip file and copy the new “RISCOS.IMG” file to the DOS partition on the SD card.

• Now copy the Raspberry Pi 4 firmware (START4.ELF and FIXUP4.DAT) to the DOS partition on the SD card.

• Edit CONFIG.TXT to add the following 3 lines to the start of the file:

[pi4]
enable_gic=1
[all]

The file should look like this when you have finished:

[pi4]
enable_gic=1
[all]
disable_overscan=1
fake_vsync_isr=1
framebuffer_swap=0
gpu_mem=64
init_emmc_clock=100000000
ramfsfile=CMOS
ramfsaddr=0x508000
sdtv_mode=2
kernel=RISCOS.IMG
max_framebuffer_width=2560
max_framebuffer_height=1440
hdmi_pixel_freq_limit=25000000000

• As a final check, the DOS partition should – at minimum – contain the following files:
  CMDLINE.TXT
  CMOS
  CONFIG.TXT
  FIXUP4.DAT
  RISCOS.IMG
  START4.ELF
  Any other files will be ignored by the Pi 4 bootloader.

Card preparation is now complete. Remember to dismount the SD card before unplugging it.

Using the SD card in the Pi 4

You will need EITHER a USB-C hub with Power Delivery (this may only work with newer Pi 4 board revisions)¹ OR an alternative method of powering the Pi 4 (e.g. via the GPIO pins) so that a conventional USB hub can be used.

1. Connect a USB hub to the USB-C (power entry) port. If the USB hub does not support Power Delivery, supply power to the Pi 4 by another means (e.g. via the GPIO pins).
2. Connect a keyboard and mouse to your USB hub.
3. Connect the HDMI cable to the left-hand HDMI port.
4. Optional – Connect the Ethernet port to your broadband router (or equivalent network port with Internet access).
5. Insert the SD card into the Pi 4 and power on. If all is well, the system will boot to the RISC OS desktop with a good screen resolution (e.g. 1920×1080).

Problems you may experience:

• A USB hub with Power Delivery may not work if you have an older Pi 4 (hardware revision 1.1 or 1.2)¹. Power Delivery should work if you have hardware revision 1.4 (as used on the 8GB Pi 4).

• You may find that the desktop is displayed at a low resolution (e.g. 640×480). You can increase this to 1920×1080 via Configure > Screen in the usual way².

¹ If you have board revision 1.1 or 1.2, you may have to supply power by another means (e.g. via the GPIO pins).

² If you are still experiencing problems with low screen resolution, have a look at the Video options page on the Raspberry Pi website.

Further information

See Using RISC OS on the Raspberry Pi for information applicable to all models of Raspberry Pi, including the Pi 4.