Michael J. Mahon wrote:
The only thing you can really eliminate is the boot ROM. The software
will still have to run the 2MHz state machine and communicate with the
PC to dump off nibble streams (that the PC could decode/encode with its
own RWTS. Essentially every function that exists in the Apple must be
provided--except the boot ROM.
Of course, if you'd like a PC emulator to be able to use the emulated
drive like a real drive, then the emulator would also have the boot ROM!
It depends if you want compatibility with protected software or not. If
you're interested only in unprotected disks, you can implement the
entire RWTS setup on a microcontroller and simply communicate this back
and forward to the PC over whatever I/O channel you prefer.
I've considered this before, and I think we've discussed it at length.
Personally I'm not interested in doing the project unless I can come up
with a way to access the disk at the nibblized level to handle copy
protection, and it remains to be seen whether or not this is feasible
over USB, where the timing is far from being deterministic. The
question of whether it is deterministic enough is probably only
answerable through experimentation - something I'm not keen on.
I have a 18F2455 lying about in case I have a brainwave. Hopefully at
some point I can study the USB specs and see what's feasible. There are
a number of transfer modes available that I simply do not understand at
this stage.