Re: RFC : SOME IDEAS FOR THE APPLE II FPGA'ers

["mdj" <mdj.mdj@gmail.com>]

Jorge Chamorro Bieling wrote:

> How much an Apple II would it be if there was no real Apple II at all ?
> The Apple II as a concept ?

In essence,  yes, although the same holds true of the accelerator card
concept. The Apple II aint much more than a 6502, expansion plane and a
video generator at the end of the day, and what you're proposing only
preserves the 'original' expansion plane :-)

The Apple II is very much a 'concept', which expands far beyond just
the original motherboards made by Apple, into the expansion hardware
made by Apple and others, and into the software. To me, the Apple II is
not it's motherboard.

> Don't you think you should "forgive" all the poor old Apple IIs in the
> world their slowness, and do the the best that you can to circumvent it,
> instead of trashing their MLBs in the first place ?
>
> I believe there's still plenty of room to speed them up a lot.

I think the already available accelerators get pretty close to 'close
enough' in terms of speeding up the Apple II. If all you achieve is
replacing these with a more accessible part, that's a worthy goal, but
I think it's a bit of a waste of what an FPGA can do

> Redesigning the slot interface because it's slow, in favor of a faster
> one, is not an upgrade, is an, I don't know,
> maybe an evolution: "Apple II EVO 4".

Not redesign, reimplement. The problem with using a slot to accelerate
the machine is that in doing so you break compatibility with a lot of
devices. You could avoid much of this by using a slot, and the original
processor socket as well, like IIgs accelerators do. But as amazing a
feat of engineering these devices are, that only applies to 1980's
engineering possibilities. They carry with them a number of issues -
break compatibility, impose power issues upon the bus, have a
aesthetically ugly and unreliable 'umbilical cord' back into the
motherboard.

The umbilical approach was the most effective solution back then, but
don't you think, had it been more economically feasibel for AE or Zip
Technologies to replace the entire board, avoid all the compatibility
issues and produce a far superior product for less money, then that's
exactly what they would've done?

I have no desire to make a 'better' Apple II compatible bus, with the
exception of making it more compatible with existing hardware than can
be achieved by retaining the existing physical implementation.

> Isn't it better to speed it up as much as possible, but trash as little
> as possible in the process ?

Yes!

> The disk II interface looks to me like the most important thing that
> should not be trashed in the process.
> It's at the same time the hardest problem.

It's the most difficult thing to virtualise, that's for sure. In terms
of not trashing it, all you need is a compatible slot for a disk II
controller, which I intend to keep.

> Even though I agree, it may not be a good idea to try to design a new
> platform. There's a thin line that has to be drawn somewhere.

Not a new platform, a modern recreation of an existing platform. I
agree there's a line that must be drawn, but in my mind, that line is
between what's feasible and what's not.

> The slot interface is not too bad, not very limiting.
> I would not like to trash it.
> In an unaccelerated Apple II, it's full potential is not achieved at
> all. It's the 6502's fault. The faster CPU controlled (not DMA)
> throughput is 1/(LDA+STA cycles) MegaBytes per second.
> This figure is a pitiful (1/8)MBps, or 125 KiloBytes per second..
>
> In an accelerated Apple II, either the STA or the LDA come/go to fast
> ram, and the other will require a single slow Apple II cycle, so it's
> throughput skyrockets to 1MegaBytes per second.. !
>
> Does not sound good enough ?

In practice (remember, there are already accelerators out there) this
doesn't happen. There is simply too much interaction with the original
I/O subsystems to get anywhere near this speed.

In practice, you have to write back to the bus a lot more data than you
think. You can't, for instance, not write back data changes to
$2000-$3FFF because graphics mode is disabled. You can't tell in
advance that the application wasn't pre-rendering. Ok, so you're
replacing the video output controller as well, that solves that
problem. You still need to write through the screen holes in the text
page. It works, but any device that 'sniffs' information about the
video buffer off the bus is now rendered inoperable.

Once you've shifted enough of the Apple II's functionality onto your
card to achieve your performance goals, you're left with the mainboard
being nothing more than 6 expansion connectors and a keyboard decoder.
Talk about a butcher job ;-)

If this were software, I'd call this approach to the solution
intractable; the complexity is just too high.

> Yes, in a sense, we are all wasting our time.

Mais non! We're stimulating our sense of creativity within a field
we're all obviously passionate about, and posing ourselves interesting
and intricate intellectual challenges. The only was this exercise could
be improved is to convert our internet connected PC's to pedal power
;-)

Matt