[Coco] Coco4 thoughts

[jdaggett at gate.net]

On 3 Jan 2009 at 22:07, Joel Ewy wrote:

> BookWorm wrote:
> >> 480Kbytes. Inside the FPGA this is easy to do.
> >>     
> >
> > Are you putting the RAM *inside* the new GIME? That woud be perfect.
> >
> > Would the CoCo 4 you're talking about use a 68000 or some imaginary
> > new chip? If it's a 68k, why not memory map it in the CoCo 3, and
> > put it on a big fat hairy new RAM board? It could share 2 meg with
> > the 6809, use your amazing new chip, or the original, and run OSk in
> > a NitrOS-9 window. This way we could still have our real CoCo 3, and
> > all that "advanced" stuff the 6809 is supposedly "too slow" for.
> >
> >   
> A 6809 core running at an effective clock rate of about 21MHz would
> probably give an 8MHz 68000 system (Atari, Amiga, original Macintosh
> come to mind) a run for its money.  And if you had a 16-bit data path
> to memory the 68K wouldn't even get points for bus width.
> 
> I've got a Digilent Spartan 3 1000K board on the way, so I'm going to
> try out Gary Becker's FPGA CoCo 3 soon.  I'll put up a blog detailing
> my experiences.
> 
> I really want to run some programs that take a lot of time on the CoCo
> and see what they feel like at approx 21 MHz.  Particularly things
> like decoding GIF files, and Sockmaster's HiColor display.  The latter
> might be a challenge because the timing will be completely off at the
> higher clock rate, and I'm not sure what the VGA timing will do to it
> as well. Oh, and then there's the fact that the CPU09 doesn't use the
> same instruction timing as a real 6809.  But I could certainly see how
> long it takes to process the image, and with a little work, adapt
> Sock's program to the CPU09.
> 
> More to come when I get my development board...
> 


Joel 

John's CPU09 is fillu spftware compatible. There should be no instruction 
changes. Yes it is true that some instructions do work with less cycle time. So 
critical timing routines will be way off at 21 MHz. 

The Spartan 3 Starter board is a nice one. I plan to migrate to the Nexys 2 
board. There I do not have to modify the board for 256 color for the VGA. It 
also has more RAM although it is PSDRAM.

james