RISC OS Open Port on the Archimedes

Dumb question, but is it technically possible to backport RISC OS 5 to the Archimedes? Just a lil bit of a thought experiment as I was tinkering with such ideas.

Not sure how far back this goes though https://www.riscosopen.org/forum/forums/1/topics/19061

Realistically no, but there is mileage in cherry-picking a number of modules from a RISC OS 5 build and integrating them with the kernel and modules from RISC OS 3.1 ROMs to form something usefully modern to create updated ROMs – see the ‘RISC OS 3.2’ project on stardot.

Three things come to mind beyond just creating a new HAL and video driver for the Archimedes:

• The ARM2 and ARM3 don’t run in 32-bit mode like later processors do.
• The Archimedes uses a separate memory controller. I think all currently supported machines use ARM integrated MMUs, so I don’t know if there’s much precedent for supporting other MMUs in the current code.
• I don’t know what the RAM requirements are for RISC OS 5. The IOMD version doesn’t specify any requirements beyond “a RiscPC or A7000”, so I’d assume it works with the earliest models with 2 or 4 MB RAM, but that’s a much more common amount on Archimedes machines.

There’s probably other stuff that I haven’t thought about, and there is still some remaining code for supporting older machines. It would be excellent to have a freely distributable Archimedes ROM that can be used with emulators, but only time will tell on what the best approach to that is.

Plus…

• Unpicking anything VIDC2 specific as the VIDC1 is a simpler beast.

• Ditto IOMD → IOC

• Plus possibly sorting out all the bits in the OS/BASIC/etc that deal with deep colours. There’s only so much you can fake via ColourTrans, especially when your best 256 colour mode is really 64-plus-tints in the bizarre/annoying VIDC1 format.

• The MEMC was mentioned above. Don’t forget it’s a bit peculiar. Which is why the page size was 8K/16K/32K depending on how much memory was installed….
• …not to mention there may need to be some sort of OS support for >4MB machines that have multiple ones daisy chained.

• Just about several billion references to the CPSR to sort out (and any MSR/MRS instructions). I’d hope most of this is hidden in CPU specific macros, but…

It’s doable, certainly, but I feel that it would likely take way more time and effort than could reasonably be justified.

I don’t know what the RAM requirements are for RISC OS 5. The IOMD version doesn’t specify any requirements beyond “a RiscPC or A7000”, so I’d assume it works with the earliest models with 2 or 4 MB RAM, but that’s a much more common amount on Archimedes machines.

Just booted RPCEmu / RISC OS 5 Direct to desktop with 4MB + 2MB VRAM and there’s 760KB free.

Just booted RPCEmu / RISC OS 5 Direct to desktop with 4MB + 2MB VRAM and there’s 760KB free.

I was using RISC OS 5 on a 4MB A7000 at the weekend and the two biggest RAM uses were: the theme sprites and the map for the harddisc.

Not loading the theme sprites will get you a big chunk back (the boot sequence skips loading them on RISC OS 3.10). There was about 1MB free on the A7000, so I’d say the minimum spec requirement for RISC OS 5 is probably 4MB.

Cameron: you have email (or see Announcements re XP1Dr2SVG).

is it technically possible to backport RISC OS 5 to the Archimedes

No. The lack of address space restricts DynamicArea creation, which in turn means anything that relies on DA’s (such as current FileCore) has to use the RMA. It also obviously means anything that relies on DA’s won’t work.

I did backport DA creation, but it’s very restricted only allowing up to 4 new DA’s and a max of 2MB to cover all DA’s – if I remember correctly.

As Stuart has mentioned the RISC OS 3.20 project was an attempt to bring the Archimedes ROM up-to-date and add TCP/IP and other modern requirements to the ROM to reduce the RAM requirement.

It’s not gained much traction though for two reasons:

1. it needs an as-yet unavailable ROM carrier to support a larger ROM
2. several RO5 Modules need recompiling to work from ROM

I’ve not updated it for several years and there are various issues I need to resolve, some of which are due to it being based on RISC OS 3.19 and other related to bugs in 26bit WindowManager etc – which might have since been resolved.

I think the last thing I did was to dynamically re-static-link C-based ROM Modules when it’s built, to allow some further additions…but it’s been a while, I don’t honestly remember.

Testing is a bit of a problem due to the lack of a carrier module for physical hardware and Arculator has a bug that causes large ROMs to fail. I think I did the bulk of the initial testing with RedSquirrel.

TCP/IP for RISC OS 3.20? Was there any pre-RISC PC machine that could use it?

TCP/IP for RISC OS 3.20? Was there any pre-RISC PC machine that could use it?

I have an R260 (A540) with network podule – I never managed to get it to work.

I have an R260 (A540) with network podule – I never managed to get it to work.

Curious – we used to use NFS over TCP/IP all the time, esp. with A540s.

Was there any pre-RISC PC machine that could use it?

Yes. I have (had?) a network podule in my A5000 that I think had some sort of flash to store modules and it worked (just about) with Windows 3.1 and 95. The details are fuzzy as it was ages ago, but it was definitely doing TCP/IP (and the hard part was getting 3.1 to do it).

On ebay “Ethernet Access Network 10 Base 2 Mini Podule Acorn A3000/3010/3020/4000 AEH72”

Curious – we used to use NFS over TCP/IP all the time, esp. with A540s.

Might depend on the podule. I came to the conclusion there was no driver for my podule. I can be wrong. Does not seem likely now I write it. Maybe not available in the standard release.

I had the R260 restored to mint condition and then left it in its box (for 30 years).