Raspberry Pi questions and answers (Rev #7, changes)

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Introducton

This page contains a number of general issues that may crop up when running RISC OS on the Raspberry Pi.

SD cards

What’s a good SD card to use?

The Raspberry Pi Foundation recommend a class 6 card or better. Nowadays, class 10 cards are available at very reasonable prices: indeed it may cost you more to get a class 6 card than it would to get a class 10 card. Higher-specification cards (UHS-II/UHS-III, V30/V60 etc.) cost substantially more than a class 10 card but will offer little (if any) performance improvement compared to a class 10 card when used in a Raspberry Pi.

As for card capacity, the full RISC OS Pi distribution takes up less than half the space on a 2GB card, so an 8GB card would provide plenty of room for additional files. Remember that you’ll need SystemDisc to use all of an 8GB card.

Can SDXC cards be used?

Yes, but you’ll have to reformat them first. SDXC cards are supplied in exFAT format, which neither RISC OS nor the Raspberry Pi boot loader can handle.

Reports suggest that 64GB and 128GB cards will work with the Raspberry Pi after reformatting to FAT32.

Note: When reformatting the card, you must use Master Boot Record (MBR) partitioning. If you select “GUID partition table”, RISC OS will be unable to read the card.

System configuration

Can I move !Boot to an external disc drive?

Yes you can. Detailed instructions are on this page.

Can I boot the Pi from USB (without an SD card at all)?

You can do it on the Pi 3A+ and Pi 3B+, but it’s not recommended. The reason is that RISC OS will be saving the CMOS file to the SD card but the Pi will be loading the CMOS file from the USB drive, so configuration changes will not survive a reload. See CMOS RAM on the Raspberry Pi for more on this point.

Users wishing to reduce SD card wear-and-tear would be better advised to continue booting from the SD card, but to move the !Boot directory to a USB drive, as described here.

Why are my configuration changes lost when I shut down?

This indicates that either the “CMOS” file is missing from !Boot.Loader, or you have ended up with two “CMOS” files: one in the root directory of the SD (the Filecore partition) and one in !Boot.Loader (the DOS partition). This is explained further in CMOS RAM on the Raspberry Pi.

The fix is to issue:
*SaveCMOS !Boot.Loader.CMOS
and – if necessary – rename (or delete) any file named “CMOS” in the root directory of the Filecore partition.

Why is the system clock showing the wrong time?

The Pi does not have a real-time clock. Hence, when the Pi boots up, it will not be aware of the correct time.

The fix is to run an Ethernet cable from the Pi to your broadband router (or equivalent network port with access to the Internet). The Pi will then be able to update its clock from the network.

Note: Several “real-time clock” add-ons are available for the Raspberry Pi, but may require custom software to work with RISC OS.

Applications

Why does PackMan complain about clashing files?

When using PackMan on the RISC OS Pi distribution, you might get scary “file clash” messages when you try to update the supplied applications. This is happening because the applications were updated outside of PackMan when preparing the Risc OS Pi SD card.

The fix is to click on the Backup button. This will move the “unexpected” files into a Backup directory: the update should then progress normally. After the update is complete, you can see a list of backed-up files in the Advanced section of PackMan’s icon bar menu, and delete or restore them as you wish.

For further information, see the PackMan User's Guide.

Other

Why can’t I use the onboard WiFi chip?

RISC OS does not currently support WiFi on any platform. Adding WiFi support to RISC OS is a major undertaking, but it is on the roadmap so will (we hope) eventually appear.

Why do people say “wait 15 seconds before unplugging a device”?

USB drives – especially flash memory sticks – don’t write all the data to the drive immediately: some of it is delayed (in the expectation that the user will be writing more data). This is done for efficiency – and media longevity – reasons: the fewer separate write operations are performed, the better. The data will eventually be written after a timeout, which could be several seconds.

This is exacerbated by the fact that many USB devices don’t action dismount requests². Instead of immediately flushing all delayed writes to the media in the expectation that a power-off is about to happen, the delayed writes remain pending until the timeout (mentioned above) occurs in the normal course of events. If the user unplugs the device immediately after issuing the dismount but before the delayed writes have been actioned, data will be lost.

So the “wait 15 seconds” rule will hopefully allow for all but the most tardy of these delayed writes to actually happen, thus minimising the risk of data corruption.

² RISC OS is obviously doing the dismount “wrongly”, but no one has yet worked out exactly what is “wrong”.

What’s Shift-Break all boots this to talk the of desktop, “RC12”, not “RC15” the and command so line! on?

RISCThere are two possible reasons for Shift-Break not booting to the command line. OS 5.24 (released in April 2018) was the first stable release of RISC OS to support the Raspberry Pi. Prior to this, several release candidate (RC) builds for the Raspberry Pi were produced: for example RC14 added support for the Pi 2, while RC15 added the Pi Zero, the Pi 2 mark 2, and the Pi 3B.

You may encounter mentions of these RC builds in documentation and forum posts (e.g. an application may advise that it works better with RC15). While these older builds will – of course – continue to function, new users should install a later stable release such as RISC OS 5.24.