Porting to Acorn

[silcreval]

I'm porting a development platform to the RiscPC (and ultimately older machines). Its a bit of a long term project - and just for fun - but I think it will be useful to developers who like to dabble. I'm not going to give details here - thats for another post - but I have a few questions.

I'd like this to be useful to as many users as possible, including the older Archimedes systems. The minimal requirements will be very low to ensure this.

My questions are :

1) what is the base RiscOS I should target ? My current system (when its working) is a Risc PC 3.7 and I have a 4.02 upgrade, but I'm guessing older machines are 3.1 or earlier. What is a good target OS as an absolute baseline that will work on any machine? I assume older machines were upgradable in some way as far as OS was concerned so the minimum isn't 1.0 ?

2) On floppy disk only platforms - I assume the older machines are floppy only - how much memory is available?

3) What is a good screen resolution and colour depth that will work on all machines?

4) Are there any good emulators for the older machines. These are hard to find and expensive so I will need to emulate these.

[IanJeffray]

1) what is the base RiscOS I should target ? My current system (when its working) is a Risc PC 3.7 and I have a 4.02 upgrade, but I'm guessing older machines are 3.1 or earlier. What is a good target OS as an absolute baseline that will work on any machine? I assume older machines were upgradable in some way as far as OS was concerned so the minimum isn't 1.0 ?

There's not much point in considering anything earlier than RISC OS 3.1 - even the earliest machines can be upgraded to (and generally are upgraded to) RISC OS 3.1. Be aware that such machines top out at 25-35MHz ARM3 and 16MB, but 8MHz ARM2 and 4MB is really your baseline. If you target RiscPC, then I'd suggest you can probably sensibly consider 200Mhz StrongARM and RISC OS 3.7 as a base level.

2) On floppy disk only platforms - I assume the older machines are floppy only - how much memory is available?

There was a very lowly 512K Archimedes A305, but I'd suggest all machines really being 'used' will now be upgraded to 4MB. Taking a machine past 4MB (except for the A540) requires significant extra 3rd party hardware, so if you're going to target earlier machines, you should really ensure things fit within 4MB.

3) What is a good screen resolution and colour depth that will work on all machines?

That's a bit trickier to answer. 640x256 was a 'baseline'. All machines will do that, at up to 8bit colour. But it wouldn't be unreasonable to target 640x480 these days. Be aware that an ARM2/ARM3 machine running 640x480 with 8bit colour will be slowed down noticably by the video controller 'stealing' RAM bandwidth from the CPU, so if you don't need 8bit, 4bit colour is a better choice - particularly on ARM2 machines. Note that on pre-RiscPC machines, 1,2,4 bit colour modes are palettised (selectable colours) but 8bit colour is essentially a fixed 8bit palette.

4) Are there any good emulators for the older machines. These are hard to find and expensive so I will need to emulate these.

Arculator is all you need. But "hard to find and expensive" isn't necessarily true...

[silcreval]

Thankyou for the above - thats really useful. More details on the project soon - I'll post them here.