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Re: FPGApple + ARM?
Jorge Chamorro Bieling wrote:
Michael J. Mahon <mjmahon@aol.com> wrote:
Of course, an FPGA is "soft" *hardware*, so it could also implement
just about any extension you could imagine.
Yes, Michael, but a-priori.
Instead, if it is being emulated you could have the instructions
redefined by the software, live, while running.
You could for example
-add custom opcodes of your own to the 6502 set
-redefine existing ones (ever wanted to branch far?), or
-define an opcode to do the job of a routine or a whole program, or
-redefine all the opcodes for those of another micro, or
-design a set of opcodes that is best suited for a particular app, or
-etc..
I guess the idea of *dynamically* changing the instruction set
still seems a little wierd. I was involved in the design of the
Burroughs 1700/1800/1900 series, which had dynamic microcode and
multiple (application language dependent) instruction sets, but
it wasn't a great idea then, and it still isn't. You need good
compilers for each variation that you design, and that is not an
easy problem. And the performance benefit is negligible, since
its all being done in software anyway.
Dynamically reconfiguring *hardware* is an idea that has had
some work done on it, but, except in special cases, it also is
regarded as not very useful in practice.
-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."