[Rpcemu] Thoughts on RPCemu development

Ed Avis eda at waniasset.com
Fri Aug 31 22:46:21 BST 2007

Tom Walker wrote:

>In my fast A5000 emulator though, I'm trapping a handful of 
>mouse SWIs and writing the Windows mouse position straight 
>into RISC OS zero page.

Ah, zero page!  I remember that from the 6502.  Didn't realize it was used on ARMs but then I never did any ARM assembler.  Is it just a case of poking x and y coordinates into a couple of addresses?  Why not do that on every mouse movement rather than trapping the SWIs?

[automated mode generation]

>To my knowledge such a utility doesn't exist - on a real 
>machine you would have to set up the sync settings as well, 
>which probably can't be reliably automated.

I remember various dodgy programs on Acorn User monthly discs and the like that would spit out mode definitions, and I used one to generate an extra large 800x288 mode or something to get the most screen space out of my CM8833.  I'll have a hunt round HENSA etc. to see which program is best.

>You'd also run into the memory limit often - A5000 hardware 
>has a limit of 480k on screen memory, and that can't be 
>changed without rewriting the memory manager.

I was wondering about that.  There was the G8 from State Machine or something like that, a more upmarket rival to the ColourCard, which required special software to use the whole megabyte of VRAM.  It does appear that 480K is a hard limit.

>For this one you'd have to trap the mode change, to set the 
>initial palette to what RISC OS is expecting. Then you'd have 
>to intercept PaletteV to redirect changes to the new 256 
>colours palette.

I see from <http://wss.co.uk/pinknoise/Docs/Arc/ColourTran/NewCTrans.html> that ColourTrans in RISC OS 3.1 is already capable of handling 256 colour palettes.  So no need to rewrite that module.  Got to admit I have no idea how to intercept PaletteV.

>I think ARX would win the uselessness stakes.

Other candidates: the Brazil monitor program included with Springboard, or indeed the new ARM7 second processor <http://www.sprow.co.uk/bbc/armcopro.htm> whose software is actually a mini RISC OS reimplementation, just enough to run BASIC.  All of these would require somewhat different hardware, of course ;-P.

I think the Amiga emulators have it easy: games on that system were usually run by booting directly from the game diskette.

>PS Register for the mailing list! I have to authorise every 
>post you make at the minute.

I've done that and also asked the list to be added to <http://gmane.org/>, if that's okay.

Ed Avis <eda at waniasset.com>

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