Showing changes from revision #19 to #20:
Added | Removed | Changed
This is the official RISC OS distribution for the Raspberry Pi.
RISC OS is a fast, compact and efficient British operating system designed specifically for the Arm processor by the same team who created the original Arm. It is developed and tested by a loyal community of developers and users.
RISC OS is not a version of Linux, nor is it in any way related to Windows. It has a number of unique features and aspects to its design which we think make it special.
Since the Pi can use pretty much any USB keyboard you might find yourself with one that isn’t arranged in the typical large PC keyboard manner. In particular non-UK Pi owners will likely be surprised when they type shift-3 and get a £ character appear instead of a #.
You can change the keyboard layout in the Configure window – double-click on the Configure icon on the desktop, click on the ‘Keyboard’ button and then pull down the menu of keyboard layout choices at the top; a USA keyboard will insert a # from shift-3. Brave people might even try the Dvorak layouts.
Another issue that might cause problems is with compact keyboards lacking a couple of function keys and a Pause/Break key. Fortunately there is a module called KeyMapper that can map one low level key to another to work around this. Put a copy of the module (not the zip file!) into !Boot.Resources.!System.350.Modules and add an obey file to load it in !Boot.Choices.Boot.PreDesk containing (for example):
RMEnsure KeyMapper 0.00 RMLoad System:Modules.KeyMapper
keymap 2 12
keymap 13 15
Here’s an explanation of what the lines in this example do:
The default settings (from RISC OS 5.24 onwards) are for RISC OS to read your monitor’s EDID and configure the display output automatically. However, it may not work properly with all monitors, and there are some aspects of the Raspberry Pi itself which can cause problems. If you are experiencing problems with your display then it’s recommended you read through this section to see what configuration options are available to you.
The section is broken down into two parts, one specific to the Raspberry Pi and one which covers settings applicable to any RISC OS machine.
There are a number of changes you can make to the config.txt file in the boot partition which will affect the behaviour of the RISC OS video driver. The most important ones are as follows:
disable_overscan
– Sick of those black borders at the edge of the screen? Try adding disable_overscan=1
to config.txt to get rid of them.max_framebuffer_width
, max_framebuffer_height
– These control the maximum screen resolution that the GPU will support. The default is 1920×1200; if the native resolution of your monitor is higher than this then you will probably want to specify the appropriate values in config.txt in order to allow higher resolution modes to be used.hdmi_pixel_freq_limit
– This controls the maximum pixel clock that the GPU will support. The default value is 162000000 (i.e. 162MHz). If you’ve had to specify max_framebuffer_width
or max_framebuffer_height
then there’s a good chance you’ll need to specify hdmi_pixel_freq_limit
as well.
pixel_rate
value listed by RISC OS will be in kHz, while config.txt requires it to be specified in Hz).hdmi_pixel_freq_limit_min
– This controls the minimum pixel clock. The default is 25000000 (i.e. 25MHz), which is the minimum officially supported by the HDMI spec. Older RISC OS software may rely on screen modes which use pixel rates which are lower than this; if you need to run such software then you can try setting hdmi_pixel_freq_limit_min
to a lower value.Note that RISC OS is now able to directly control the timings of the signal that the GPU sends to your monitor. This means that some config.txt settings, like hdmi_group
and hdmi_mode
, are effectively ignored. Instead, you will want to configure the screen mode through RISC OS, as described below.
If you want to revert to the old behaviour, you can do so by adding disable_mode_changes
to the first line of the cmdline.txt file in !Boot.Loader (create the file if it does not already exist). The net effect of adding disable_mode_changes
is:
hdmi_group
and hdmi_mode
settings).To examine or edit files in the boot partition from within RISC OS, open the filer window for the SD card by clicking on the “:0” icon on the icon bar, shift- double-click on the !Boot application to view its contents, and then double-click on Loader. Because RISC OS uses dots for directory separators, config.txt will appear as config/txt.
The screen setup plugin in !Configure is the main place to make changes.
RISC OS should be using EDID by default, but to ensure it’s enabled you can try following the steps below.
If the initial splash screen appears low-res or blocky after enabling EDID, the settings in the CMOS RAM may1 be incorrect:
1 If your monitor is slow to start up, RISC OS may select a “fallback” (low-resolution) startup screen, temporarily ignoring the EDID settings. You should still be able to select a higher desktop resolution from the “Monitor type” menu in !Configure, as explained above.
You can disable EDID and specify all the settings manually by selecting any of the other monitor types listed within Configure. Each of the monitors listed will correspond to an MDF (Monitor Definition File) contained in the !Boot.Resources.Configure.Monitors
folder – if you have an MDF that’s suitable for your monitor then you need to add it to that folder in order for Configure to be able to find it.