USB Universal Floppy Disk controller - test-drb@ccmp.vtda.org

14 Mar 2005

...
 From: "9000 VAX" <vax9000 at
gmail.com>

On Mon, 14 Mar 2005 20:51:10 +0000, Jules Richardson 

 What about cost? (irrespective of how the device physically connects to
 the host machine)

 I forsee four goals to make it useful:

   o  Cheap
   o  Simple to build by anyone with a few electronics skills.
   o  Open 'source' (all schematics etc. available)
   o  Easy / quick connectivity

 Catweasel seems to lose out on 1, 3, and 4 - and 2 isn't relevant in its
 case. Can't comment on how nice its software API is as I haven't looked
 at it yet, but doubtless a bunch of us on this list could come up with
 something that'd cater for all tastes (plus the really low-level
 software would all be open source anyway!)

 Personally I'm not a fan of a USB version though; I'd rather have
 parallel as pretty much any machine has a parallel port - USB limits me
 to newer PCs and Macs (plus software interfacing *might* be harder).

 Priorities seem to me to be (highest first):

   o  Reading disks
   o  Writing back a disk image
   o  Decoding disk data on host machine
   o  Modifying disk data on host machine, re-encoding back to floppy

 Happily, that's probably order of complexity too, easiest first :) (I am
 coming at this from a preservation point of view, rather than being able
 to create disk images for use with emulators, say) 
Luckly I have experience with both ADSP2181 and a CPLD/FPGA. I built
my own little board to read out the internal memory from an ADSP2181,
designed signal generation board with ADSP2181, and wrote thousands of
lines of ADSP2181 code. On the other hand, I built a QBUS MSCP SCSI
with Xilinx CPLD and now working on an Altera CPLD.

I didn't read much of floppy controller but in my preliminary opinion,
CPLD/FPGA is a better fit. If you use a 2181 here, you utilize only
the (synchronous) serial port which can be easily built with a CPLD. A
CPLD on parallel port has another advantage, that you might be able to
eliminate a microcontroller which I guess is needed for a USB
sollution. I don't have knowledge of USB so please correct me if I am
wrong.

vax, 9000

Hi Vax
 What you say is true. I would suspect that it would be
possible to do all of the work in a CPLD, even for the
USB chip that I saw. Still, the ADI device has enough horse
power to do a lot of data reduction. It also has the
possibility to handle the writing back to a disk,
including pre-comp. Again, all this has the possibility
to be done in the CPLD as well but I think that incremental
development in a software environment is easier than
...
 from a Verilog/VHDL level.  I expected to use the
processors ability to analyze the
data to help to do data reduction from an over sampled input.
This could be done on a PC with just the raw data as you
state( again, even with the CPLD ). USB might not be fast
enough to handle the over sampled data. By local data
reduction, one can minimize the buffering requirements.
 In order to make a open source that all can use, you'd
need to provide a compiler. ADI gives one an assembler
that can be use for free.
 Still, if you went ahead and did this on your own, that
would be great! I'm not sure if I could find the time
to fiddle with it for at least a few months. All efforts
here will be greatly appreciated. Having the code in
Verilog/VHDL would also help to avoid obsolescent.
Chips like the ADI2181 only have a few years before being
obsoleted. Both should have the advantage that one can
add enhancements as other types of disk media are added.
Dwight