Re: A 6502 emulating a VIC-II (sort of)

Michal Pleban wrote on 05.06.2022 21:17:
> tokafondo wrote on 05.06.2022 21:04:
> 
>> But there would be also fast graphics routines that would be executed 
>> by that 6502 and not the main one, because that graphics 6502 would 
>> run several times faster than the main CPU. The VIC-II actually run at 
>> ~8MHz, didn't it?
> 
> What you are asking for kind of already exists. It's called Parallax 
> Propeller. It is a RISC CPU that is meant to emulate I/O chips in 
> software. It has lots of instructions specifically tailored to emulating 
> I/O.
> 
> So now, let's put things in perspective. The Propeller in my CBM-II VGA 
> interface runs at 80 MHz which is the maximum. To be able to emulate a 
> monochrome text-only 80x25 screen at 640x480 VGA resolution, I need to 
> have four threads (out of 8 available) - one to actually output the data 
> into the DAC and three to render the data based on the text screen - 
> because one is too slow, there needs to be a pipeline of three.
> 
> Now that's (a) without color (b) text-only and (c) without sprites. This 
> very simple task already occupies 50% of an 80 MHz RISC chip that is 
> specifically made for this kind of solution. If you wanted color, 
> graphics and sprites, you would need at least an order of magnitude 
> higher clock, which is not available. And I think that's actually still 
> too low, because sprites are VERY hard.
> 
> So, unless your 6502 is clocked in the GHz area, no way.
> 
> Regards,
> Michau.