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Re: RFC : SOME IDEAS FOR THE APPLE II FPGA'ers
Jorge Chamorro Bieling wrote:
mdj <mdj.mdj@gmail.com> wrote:
(Pardon me for responding to both the quoter and the quotee...)
I like the idea of fitting in a standard slot except, in terms of
complexity, it's almost equivalent to an FPGA based replacement board,
and in some ways is actually harder. For one, you have to design the
layout in such a way that it doesn't foul anything up when plugged into
a real Apple II. Secondly, you're constrained your options in terms of
acceleration, since you have to operate in terms of the real Apple II
environment to remain compatible with the bus. This means that many
potential acceleration ideas are unimplementable,
How much an Apple II would it be if there was no real Apple II at all ?
The Apple II as a concept ?
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 agree, and also doubt the real-world benefits of speeding them up
beyond, say, 20MHz.
It would be crazy to throw out the baby with the bathwater, just to
get the possibility of a 200MHz processor that no one could tell was
running that fast when actually using the system.
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".
Isn't it better to speed it up as much as possible, but trash as little
as possible in the process ?
You can't speed up the Apple bus without obsoleting almost every
card ever made for it. That is a non-starter.
You could, in principle, add a second, faster peripheral bus for future
expansion, but that would be expressing what I fear is an unreasonable
hope.
and worse, you have to accept all the compatibility restrictions that
existing accelerators have.
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.
And it keeps the bus at 1MHz, for sure.
So, implementation complexity goes up, and the quality of the end
solution goes down. Maybe I'm underestimating the complexity of
replacing the whole board a little bit, but I think that worst case, we
end up with a far more flexible solution for commensurate effort.
Flexibility for flexibility's sake is a fool's errand. The Apple II
is already a marvelously flexible design.
Try this. Construct some actual use scenarios and then evaluate them
against some "extension" ideas. Try out different processor speeds--
1MHz, 10MHz, 100MHz, 1000MHz. Try out different memory capacities--
1MB, 10MB, 100MB. Try out "Apple bus compatible" and "non-Apple bus
compatible". See what use scenarios benefit from various choices.
But *don't* assume a boatload of new software to take advantage of
whatever new goodies you can imagine--because we all know that it
won't--can't--happen. (This restriction actually simplifies the
construction of realistic use scenarios considerably.)
For example, consider an Appleworks 3 user with a 500KB database or
spreadsheet. Consider a die-hard developer assembling a large program
or compiling a big Pascal program. Consider a game player trying to
get to level 9 of something.
Now measure the use of various system resources, identify bottlenecks,
and evaluate the performance characteristics of an "extended" system
under various design alternatives.
This methodology will give you a real handle on the cost-benefit
tradeoffs that any real design effort must make--and it will be
enlightening.
"A system-level problem is almost never what you think it is."
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.
The slot interface is not too bad, not very limiting.
I would not like to trash it.
Yay!
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..
Yep, Zip Chips help! Of course, that bus is running flat out while
achieving 125KB/sec, fetching instructions--which is why caching is
such a help.
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.. !
Actually, only the loads go to fast RAM, the stores usually go to both
fast RAM and to the bus--you never know who's listening. ;-)
Does not sound good enough ?
I think a 20-25MHz "Zip Chip" would be a wonderful thing. DMA
compatibility is of marginal value with fast programmed I/O.
Getting something operational can happen relatively quickly, and adding
mind boggling performance enhancements down the track is relatively
easy. Nobody's end goals are compromised, and virtually no extension
that any of us can dream up is made difficult/impossible. It's a
win-win
Except that this approach throws out the many hundreds of existing
Apple II peripherals--bad trade.
In fact, the only real 'downside' I can see to this approach is that
once such a thing exists, it pretty much destroys the 'market' for any
future, and possibly existing Apple II expansion hardware. But then,
from my perspective, this is actually a good thing, since ultimately
consolidating everything into a unified solution creates a larger
'potential' market, since people don't have to wait a potentially
endless amount of time to acquire the system they'd like, by competing
with everyone else for the precious few components that appear on ebay
each year.
So much for the "joy of the hunt"... ;-)
A new platform... ?
Sounds like it. And how is this different from a good emulator running
on a modern system? It seems to have all the same limitations in terms
of driving Apple peripherals and cards. And it is hard and not done,
while emulators and modern platforms are easy and done!
I would however like to highlight that when it comes to the Apple II,
that I am in no way motivated by profit, only love, and when
considering the way anything I'd like to be a part of reaches the
supposed 'market', think "Apple ][ Reference Manual"
Yes, in a sense, we are all wasting our time.
As long as we're enjoying it, it isn't wasted...
-michael
Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it is seriously underused."