[Coco] Why do we need a CoCo 4? (Long irrelevant rant)

[jdaggett at gate.net]

On 29 Dec 2008 at 11:00, Bill Barnes wrote:

> The PLUS to the fpga idea is, we can extend the 6809/6309 core, if
> need be to include real 16-bit and even possibly 32-bit operations by
> creating op-codes that the 6809/6309 haven't used or reserved... we
> could have a 681609 or 631609 on our hands that way. Possibly using
> the 6309 trick and have a third mode (6809,6309,631609).

Yes one could expand the 6809 core. As far as I know there is no 6309 IP 
core in existance, yet. What I have coded is still early in design. The 
register stack and the ALU are rather easy to code. Doing the rest and 
achieving decent speed is a bit more taxing. Right now the ALU has a max 
of  10 nS combinatorial delay from input to output. Now to get the rest to 
move that fast. 

Yes I have ideas of what could be done to improve the 6809/6309 core. 
One would be to do what RISC controllers do, pipeline fetches. That is 
doable in an FPGA. 

Multimode processor is doable but would take up a lot of resources on the 
chip if there is significant differences. That now takes the computer out of 
the realm of hobby sized FPGAs and what could be done in a QFP 
package. Very large FPGAs , >500K gates, are all BGA package. That 
requires 6/8 layer PCB design. One alternative is to code the processor in 
such a way that when you synthesize it you can tell it which processor you 
want. This is done with one core that is either a Z80, 8080, fast Z80 or the 
GameBoy processor. That core runs at 35MHz. I also have a core that is 
selectable for a 6502, 65C02, or 65C816 by two pins.

To do an enhanced opcode is really a nightmare in getting consesus on 
what to add and what not to add. Personally I would like to see more 
instructions like that in the HC11/HC12. BRCLR and BRSET are nice 
instruction. The IDIV and FDIV are more fucntional than what the 6309 
has. That also requires someone to rewrite assemblers and any compilers 
for new instructions. That is out of my realm of expertise. I am a hardware 
dude that can do some programming. 

james