Re: An USB interface for Disk2?

["Bryan Parkoff" <nospam@nospam.com>]

Mike,

> Quite a few interesting ideas here.
>
> I'm not sure that the whole track approach would work all that well. For 
> reading, you have to know the sector layout or at least the number of, and 
> how to identify sectors, in order to determine when you have circled 
> around and have completely finished reading the track.  One you have done 
> that, you might as well read and write sectors.
>
> This implies implementing at least part of the RWTS in the 
> micro-controller, which doesn't bother me, too much.  However, copy 
> protected SW may require a special RWTS implemenation in order to be read.
>
> So far, high level analysis make me think that a modern micro-controller 
> should have plenty of power to accomplish the job of the Disk II 
> controller hardware and the RWTS, without significant additional HW 
> assistance.
>
> The USB mass storage option may be an interesting way to go, but I'm not 
> particularly excited about delving too deeply into USB having spent some 
> fustrating time at work trying to manage a project that involved an USB 
> device interface.  However, it may be worth the effort and some kind of 
> translation from USB mass storage to what essentially is RWTS should be 
> doable.

    I think what you refer standard RWTS and special RWTS are not important. 
The important is the timing.  Disk II micro controller card uses 2 MHz.  It 
is a good idea to put 14.3MHz osc chip in the USB printed circuit.  Let 
14.3MHz osc chip runs at 2 MHz endlessly in a loop.  Only six commands (I 
don't remember the total commands.) can be responded through USB.  Six 
commands controls Disk II in hardware to respond read, write, and seek, etc. 
Then data is read from floppy disk and store it into RAM buffer before data 
from RAM buffer is ready to be transferred to PC RAM through USB cable.  The 
Apple II Emulator is ready to read PC RAM.
    The problem is that PC has different timing like 3GHz.  It is too fast. 
RAM buffer is designed to wait for the commands before data from RAM buffer 
can be read from or write to floppy disk at 2MHz.  I am sure that 
copy-protection floppy disks will work.
    I suggest to rethink the design of USB for Disk II using RAM buffer. 
RAM buffer contains the information in track and sector.

Bryan Parkoff