Actually, after looking at the code I thought most of the instructions
wouldn't be that difficult. SLEEP would require a little work to
fully implement but imitating it's functionality from a software
viewpoint might not be so bad.

As for mmu every address decode has to use the mmu registers... which
may or may not be a big deal. I just started to look at the code so I
really don't know yet.

Serial ports should be simple.

--- In zxgate@yahoogroups.com, "Andrew McMeikan" <andrewm@o...> wrote:
> MMU and serial ports are likely a lot simpler than the instruction
> set. I am into Z180's so I'll probably try to do something there but
> I am not so experienced.
>
> I have just recently got some larger fpga's so will be doing some
> more soon, a 16k zx81 fits very comfortably in a XCV1000E, 8K Ram
> zx81 fits in a XCV800.
>
> I can not fit things in as well as Daniel as I am only using xilinx
> tools.
>
> I think I will try some of the onchip stuff from the z180 but I am
> not up to tackling the microcode yet.
>
> In the meantime I am seeing how fast I can get a ZX81 to go in fast
> mode (anyone got a use for a 200Mhz ZX81?)
>
> cya, Andrew...
>
> --- In zxgate@yahoogroups.com, "James Diffendaffer"
> <jdiffendaffer@y...> wrote:
> > Have you worked on any of this? I'm mostly interested in the TRS80
> > since it's what I learned to program on. I am also interested in
> > adding 64180 compatibility to the processor core... however I'd
> > probably just start with instructions rather than the MMU, serial
> > ports, etc.
> >
> > --- In zxgate@yahoogroups.com, "Daniel Wallner" <jesus@s...> wrote:
> >
> > > I will make sure that the
> > > Spectrum's RGB and S-Video outputs work and possibly fix the ZX81
> > > and TRS80 problems but that's it.
> > > Only the ACE is at the moment complete and there are lots of
> things
> > > to do, especially on the TRS80 and the Spectrum.
> > > Is anyone interested in doing this?