RPCEmu and RISC OS 5 on Mac OS X (Rev #12, changes)

Introduction

History, RISC OS 5 and software compatibility

Early ARM processors had a combined 26-bit program counter and status register, rather than separate 32-bit program counter and status registers.

For a time processors had both 26-bit and 32-bit modes, with the former being phased out by ARM. In October 2002 RISC OS 5 was released using only the 32-bit mode, required because 26-bit mode processors were no longer available – the last being the StrongARM used in the RiscPC.

Most software written in BBC BASIC has no compatibility issues, and in many cases software written in C merely requires a recompilation of the source code, where available. However, some software is reliant on features specific to 26-bit mode and needs updating before it will work.

Recent developments have made RISC OS 5 available for the RiscPC (StrongARM/ARM610/ARM710) and A7000/A7000+ (ARM7500/ARM7500FE).

A ROM upgrade is available to install on real hardware. The following installation notes will allow you to run RISC OS 5 on an emulated RiscPC on a Mac running macOS.

These notes are based on testing

• The authors of this installation sequence have been using RPCemu on Mac OS X for a number of years, under Snow Leopard, Lion, Mountain Lion and Mavericks (10.9), without issue.
• A development build of RPCEmu 0.9.3 for 64-bit versions of macOS is now available. This build is known to work on macOS Mojave (10.14), macOS Catalina (10.15) and macOS Big Sur (11.2).

Installing RPCEmu from scratch

If you have an older version of RPCEmu already installed, see Upgrading from an older version of RPCEmu below.

Installation

1. Download the zip archive of RPCEmu 0.9.3a – be sure to get the ZIP archive, not the DMG package.
2. Open the zip archive, and copy the applications “RPCEmu-Interpreter” and “RPCEmu-Recompiler” to the Applications folder (either drag them over the Applications entry in the Finder sidebar, or onto the Applications folder on the dock).
3. Create a data folder within your Documents folder (e.g. Documents/RPCEmu) and copy the contents of the “Data” directory from the RPCEmu distribution archive.
4. Download an IOMD ROM image from the downloads page. The recommended ROM is labelled IOMD 5.28 stable (softload).
5. Unpack the ROM archive and copy the file “riscos” from \soft\!Boot\Choices\Boot\PreDesk\!!SoftLoad\riscos /soft/!Boot/Choices/Boot/PreDesk/!!SoftLoad/riscos into the Documents/RPCEmu/roms directory. The other files aren’t needed and can be discarded.
6. Download a HardDisc4 image from the Miscellaneous downloads page. The recommended version is labelled HardDisc4 (self-extracting) – this should give you a file called “HardDisc4.5.28.util”.
7. Copy this file to Documents/RPCEmu/hostfs as “HardDisc4-util,ffc” – take care to keep the ,ffc (comma ffc) ending which will be translated by RPCEmu to produce the metadata filetype for RISC OS.

Configuration

1. Open the Applications folder and double-click on the RPCEmu-Recompiler icon to launch it (you may need to right-click and choose Open for the first time, as newer versions of macOS try to discourage running potentially unsafe code).
2. A dialogue box will appear, asking you to choose a data directory – choose the RPCEmu folder created earlier.
3. Ignore the TaskManager error and click on the RPCEmu item in the menu bar and then Preferences…
4. Select the SA110 (StrongArm) processor option, select 128MB or more RAM, and 2MB VRAM. You may also wish to enable sound.
5. Quit and re-open RPCEmu (it may not auto-restart for you).
6. After the restart the emulator will stop at a * prompt. This is because the system is not currently configured correctly to boot into the desktop – type desktop to start the desktop GUI. Cancel the error ‘Machine startup has not completed’.
7. Click HostFS, on the iconbar, to open the root directory.
8. Double-click on the HardDisc4-util to extract the HardDisc4 contents. Wait a while. Double-click the HardDisc4 directory that has been created to open it. Cancel the error ‘No Boot application has been run’, and hold shift down while dragging the entire contents of HardDisc4 to HostFS:$ (this moves, rather than copies, everything to the root).
9. Press f12 and issue the following commands
   Configure FileSystem hostfs
   Configure Boot
10. Press enter twice to return to the desktop then press ctrl-shift-f12 to shutdown.
11. Click the macOS Close button.
12. Click on the RPCemu-Recompiler icon in the Applications folder to re-launch RPCEmu.
13. When RPCemu is launched, it should now boot to the desktop. All further configuration of RISC OS is personal preference. Access the configuration section of RISC OS by a single click of the Menu (middle) mouse button over the cog icon on the far right of the iconbar.

Networking

The explanation over on the RPCEmu web site works reliably on the NAT option, but the bridging option is untested.

Briefly it comes down to this:

Emulator configuration
Run RPCEmu and open the networking configuration (up on title bar)

1. Click Settings
2. Click Networking
3. Select the “Network Address Translation” option and click OK). OK.
   The Emulator will restart.

RISC OS Networking Configuration
When RISC OS has rebooted, click the “Menu” (middle) button on the mouse over the Switcher icon (cog on the right of the icon bar – bottom right of screen) and the select the Configure option in the menu.

1. Click the Network icon in the window that appears.
2. Click the Internet icon in the window that appears.
3. Click Enable TCP/IP Protocol Suite, then click the Interfaces icon.
4. In ‘Interfaces’ make sure EtherRPCEm is selected and click the Configure… button.
5. Choose DHCP; and Click Set. The window closes.
6. Click the close option in the Interfaces window.
7. Click the close option in the Internet window.
8. Click Save in the Network window.
9. Click “Reset now” in the window that appears.

Testing
After the reboot press Ctrl and F12 simultaneously to reach a task window showing a command prompt.

• Type ifconfig -a
  The response should show the rpcem0 interface has an address of 10.10.10.10

• Type gethost www.google.com
  The response gives the IP address of the www server at google.com domain

• Type gethost -t www.google.com
  The response will now include the time it took for your DNS server to respond.

• Type gethost -x -t 8.8.8.8
  The response will give the hostname (it’s dns.google) of the address you typed typed, and the last line will be the time it took for yourDNS server to respond.

Limitations

• The emulator does not support IDE harddiscs hard discs orCDROM. The OS does, but the emulator has a data loss bug.
• If you do not configure the emulator to use 2MB VRAM, you may get redraw issues in the RISC OS desktop.
• The Restarting Restart button, on the Shutdown window, should be avoided, because it seems not to reset everything.RISC OS (Ctrl-Break, the Restart button on the Shutdown window, SYS “OS_Reset” etc.) does not work properly – you will get a “Bad PC” error from RPCEmu. Instead, you should shut down RPCEmu and restart RPCEmu.
• As stated at the top: RISC OS 5 uses the processor in 32 bit mode. There is no provision for mixing 26-bit mode and 32-bit mode applications on the same machine – legacy applications will first need updating.

Networking limitations

• Using the NAT option you are hidden from your local network network, so sharing of resources between the emulator and other computers on the network does not work.
• The NAT setup uses one specific IP in a /24 subnet (10.10.10.0/24), if your local network uses this same range this networking setup will not work. Change your router settings to use a different IP range.

Upgrading from an older version of RPCEmu

• Obtain the RPCEmu distribution archive “RPCEmu-0.9.3a-Release.zip” as mentioned above.RPCEmu-0.9.3a-Release.zip as mentioned above.
• Delete (or move elsewhere) your existing versions of “RPCEmu-Interpreter” and “RPCEmu-Recompiler” – they are most likely to be installed in the “Applications” folder.
• Install the updated versions of “RPCEmu-Interpreter” and “RPCEmu-Recompiler” in the Applications folder.
• In your existing Data directory, create a “netroms” folder (alongside “hostfs”, “poduleroms” and “podules”).
• Copy “EtherRPCEm,ffa” from the “netroms” folder of your RPCEmu distribution archive to the “netroms” folder you just created.
• Open the Applications folder, right-click on “RPCEmu-Recompiler” and choose “Open”. Acknowledge the warning screen(s) that appear.
• Double-click on “RPCEmu-Recompiler” to launch RPCEmu. This should load to the RISC OS desktop.
• You may need to enable networking, as explained above.

After starting RPCEmu, you may discover that “mouse capture” mode is not working properly. To fix this, proceed as follows:

• Go to System Preferences > Security & Privacy > Privacy > Accessibility and untick the entries for “RPCEmu-Interpreter” and “RPCEmu-Recompiler”.
• Close the System Preferences window.
• Start RPCEmu and untick “Follow Host Mouse” so that macOS is aware that RPCEmu wants to control the computer.
• Reopen the System Preferences window and tick the entries for “RPCEmu-Interpreter” and “RPCEmu-Recompiler”.System Preferences > Security & Privacy > Privacy > Accessibility and tick the entries for “RPCEmu-Interpreter” and “RPCEmu-Recompiler”.