Floppy to FPGA?

I'm currently working with an old imaging device whose only output is a
floppy drive which only allows transferring 6 images at a time (due to
floppy disk size constraint). I had the idea of implementing an FDC
(floppy drive controller) on an fpga then connecting the drive cable to
the fpga and using the fpga to stream the images through a serial port
thus bypassing the disk size constraint. Can anybody comment on the
feasibility of this project and perhaps point me to some existing VHDL
code? Otherwise, does anyone have any other feasible ideas?

    Thanks.

fslearner <junkaccount616@gmail.com> wrote:
>I'm currently working with an old imaging device whose only output is a
>floppy drive which only allows transferring 6 images at a time (due to
>floppy disk size constraint). I had the idea of implementing an FDC
>(floppy drive controller) on an fpga then connecting the drive cable to
>the fpga and using the fpga to stream the images through a serial port
>thus bypassing the disk size constraint. Can anybody comment on the
>feasibility of this project and perhaps point me to some existing VHDL
>code? Otherwise, does anyone have any other feasible ideas?

Implementing an fdc controller in fpga should be a piece of cake. The signal
is 1 Mbps at tops asfaik. It's proberbly MFM encoded signal, otherwise it's
likely GCR or FM. 1.44M/1.2M discs are 500 kbps. 720k/360k = 250 kbps.

The signal consists of a pulse for every magnetic flux asfair. If you use an
oscillator to count the number of clocks between these pulses. You can derive
data from there.

On a higher level you have to pay attention so that your host only read disc
data when it has been completed, and fat is consistent. Should you erase
or in other way alter "floppy" your scanner device better be aware of this.
Through the signal 'discchange' wire or simply instruct it on console.
Your fpga can also imitate two floppys btw, by useing the select signals.

A quick approach is to add one those usb-fpga kits. And tie floppy i/o to it.

Don't forgett that floppy idc36 is 5V.. ;)

fslearner schrieb:

> I'm currently working with an old imaging device whose only output is a
> floppy drive which only allows transferring 6 images at a time (due to
> floppy disk size constraint). I had the idea of implementing an FDC
> (floppy drive controller) on an fpga then connecting the drive cable to
> the fpga and using the fpga to stream the images through a serial port
> thus bypassing the disk size constraint. Can anybody comment on the
> feasibility of this project and perhaps point me to some existing VHDL
> code? Otherwise, does anyone have any other feasible ideas?
>
>     Thanks.

should be doable. there is one guy who has floppy disk host interface
done by 100% software with some small microcontroller. So with FPGA
you defenetly can do it. but I bet you need todo it all from scratch.

Antti

 "Antti" <Antti.Lukats@xilant.com> wrote:
>fslearner schrieb:
>
>> I'm currently working with an old imaging device whose only output is a
>> floppy drive which only allows transferring 6 images at a time (due to
>> floppy disk size constraint). I had the idea of implementing an FDC
>> (floppy drive controller) on an fpga then connecting the drive cable to
>> the fpga and using the fpga to stream the images through a serial port
>> thus bypassing the disk size constraint. Can anybody comment on the
>> feasibility of this project and perhaps point me to some existing VHDL
>> code? Otherwise, does anyone have any other feasible ideas?
>>
>>     Thanks.
>
>should be doable. there is one guy who has floppy disk host interface
>done by 100% software with some small microcontroller. So with FPGA
>you defenetly can do it. but I bet you need todo it all from scratch.
>
>Antti

Doable, no doubt, but you need more information than just the specs of
the interface between floppy and controller.
With an FPGA you can recover the raw data sent to the floppy as well
as the head positioning and motor on/off commands.
You will need details about the file system structure in the floppy to
allow you to interpret these data and commands to recover the files
you want to send out.

As an aside, I worked for a company that made a system that simulated
a magnetic tape drive, for similar purposes.
Instead of filling a tape reel and then remove it and physically
transport it to a different location to process the data, "fake" the
drive, collect the data from the tape interface and stream it over the
Internet for processing.

fslearner wrote:
> I'm currently working with an old imaging device whose only output is a
> floppy drive which only allows transferring 6 images at a time (due to
> floppy disk size constraint). I had the idea of implementing an FDC
> (floppy drive controller) on an fpga then connecting the drive cable to
> the fpga and using the fpga to stream the images through a serial port
> thus bypassing the disk size constraint. Can anybody comment on the
> feasibility of this project and perhaps point me to some existing VHDL
> code? Otherwise, does anyone have any other feasible ideas?
>
>     Thanks.

Steve Wozniak designed the Apple II floppy disk interface, many years
ago, using a few TTL chips, IIRC.

Leon

fslearner wrote:
> I'm currently working with an old imaging device whose only output is a
> floppy drive which only allows transferring 6 images at a time (due to
> floppy disk size constraint). I had the idea of implementing an FDC
> (floppy drive controller) on an fpga then connecting the drive cable to
> the fpga and using the fpga to stream the images through a serial port
> thus bypassing the disk size constraint. Can anybody comment on the
> feasibility of this project and perhaps point me to some existing VHDL
> code? Otherwise, does anyone have any other feasible ideas?
> 

My understanding is that you want to create a replacement device for
the floppy drive so that you can stop having to shuffle data back and
forth.  This would mean that the FPGA device would have to fully
emulate drive and the disk itself and to be completely transparent to
the test equipment that you are using.  That's not a trivial project.

Why not just use something like the Delkin Flashpath SmartMedia Floppy Adapter
http://www.amazon.com/gp/product/B00000JI3H/002-8914784-7568866?v=glance&n=172282
it looks like you might need to add a driver to the system, but your test
equipment is likely running Windows under the hood anyway so this might be
possible.

If your test equipment has a spare IDE location then you could also just use
a straight IDE to CompactFlash like this one.
http://www.acscontrol.com/Index_ACS.asp?Page=/Pages/Products/CompactFlash/IDE_To_CF_Adapter.htm

Ed McGettigan
--
Xilinx Inc.

"Leon" <leon.heller@bulldoghome.com> writes:
> Steve Wozniak designed the Apple II floppy disk interface, many years
> ago, using a few TTL chips, IIRC.

Five TTL chips, one 555 timer, and a 256x8 PROM for a state machine.

There is a second 256*8 PROM to store boot code, but that is logically
independent of the disk controller functionality.

However, the reason this worked is that it didn't have to be compatible
with anything else in the world.

The trick to making a good FDC is having a robust data separator.  Simple
techniques don't work well with marginal cases.  Even a single DPLL doesn't
solve the problem, because you need to deal with pulse shifting from the
magnetic media independently of tracking frequency variations due to motor
speed.  A second-order DPLL works pretty well though.  There was a lot of
work done in this area in the 1980s.  WD and SMC had US patents (which should
have expired by now) on some clever second-order DPLL designs.

Odds are, this equipment is way too old to have a 3.5" floppy -or- an
IDE port.  Most likely, it's a 5.25" inch drive, mayby FAT12 360K,
mayby not.

It's still very doable.  I've done something almost the same to the MFM
interface on an old hard disk drive.

Snag the -entire- data stream, sector/track headers and all into
memory.  A 360K floppy will fit into 1/2 meg of memory.

Use a micro to sift through the image to find the data fields of the
sectors.  Then find the file system in those.

If the micro has a usb port, you can emulate a flash key.  Or write out
to a SD/MMC card.  Or whatever.

It was a fun project; remember that the device will be reading as well
as writing, if there's a file system on the "disk".

I remember seeing someone already did it, but with a microcontroller 
rather than an FPGA. Google for "semi-virtual disk". It is using an 
Atmel AVR uC to simulate a floppy. Works for both FM and MFM formats.

-Alex.

Alex Freed <alexf@mirrow.com> wrote:

>I remember seeing someone already did it, but with a microcontroller 
>rather than an FPGA. Google for "semi-virtual disk". It is using an 
>Atmel AVR uC to simulate a floppy. Works for both FM and MFM formats.

http://www.thesvd.com/

Seems to be a PIC 16C65b @ 20MHz + 256kByte sram in essence.

Schematic+PCB:
  http://www.thesvd.com/SVD/Downloads/SVD-Instructions.pdf