[Coco] Status update and your input on the Floppy Disk Controller emulator for the CoCo

[Frank Pittel]

Steve,

When you first mentioned the concept I misunderstood what you were doing
and thought that it would be just a floppy controller and I wasn't interested
since I already have a bunch of them. :-) What you discribe here is very different
then what I first thought. I also like the idea of keeping it simple. Get
something out the door now and add features later as they make sense!! I would
suggest that you stick with the fat filesystem of the cards and use the .dsk
format. That way us linux users can backup the cards and existing tools would be
able use the "disks" directly without the need for additional tools.

I hope that you get something out soon and look forward to getting one!!

The Other Frank



On Wed, Jun 01, 2011 at 12:04:26PM -0700, Steve Bjork wrote:
> Earlier this year, work start on a Floppy Disk Controller emulator
> for the CoCo. This device would plug into a CoCo and emulate the
> functions of the Western Digital Floppy Disk Controller and Floppy
> Disk Drive. In place of the Floppy media, the device would use a
> SDHC memory card to store the floppy disk data.
> 
> Since the device would emulate the WD1793 and the other components
> on the Tandy Floppy Disk controller, it will work with most color
> computer software without any software patches. (Even most copy
> protected software.)
> 
> At the last CoCoFest, I received a lot of helpful input on the
> device. Some of the ideas ranged from adding a Network interface to
> talk to a host computer to a video circuit for 256 colors. But the
> best suggestion was KIS (Keep It Simple) so the device could be
> designed and build in the shorted time possible.
> 
> With the fact that others are working on both USB and Network
> interfaces for the CoCo, there is no need for the FDC emulator to
> anything more than the FDC and SDHC memory card. There will be a PC
> program for transferring data to the SDHC card and back. You could
> even use DriveWire or CoCoNet to talk to Host PC and will using the
> FDC emulator. These options should handle any need to talk to a host
> PC for getting data to and from the device.
> 
> The current design uses two micro-controller. The first is a small,
> but very fast chip to emulate the WD1793 and Tandy logic of the FDC
> pak. The second micro-controller handles the track format and data
> information stored in the SDHC card. The total cost of both
> micro-controllers cost less than $10 in single unit quantities.
> 
> The FDC emulator will have a number of setup switches and LEDs for
> configuring and status information. The first four switches will be
> the disk write protect switches. (Much like the write protect tabs
> on a floppy disk.) An eight way switch is the Boot configuration
> selector to load one of eight different drive/disk configurations
> with an auto boot option. A special “write protect all” switch that
> will keep the SDHC from being wrote to even if the CoCo start
> running bad code. (Handy for writing test code.) The LEDs will
> display drive motor on and Access for of the four drives plus a SDHC
> write protected status and access lights.
> 
> In addition to the FDC emulator mode, the device can run in special
> transfer mode for maxim throughput to the SDHC card. The
> applications of this mode range from OS-9 drivers to John W.
> Linville’s CoCo Video Player.
> 
> With the basic design of the FDC emulator now locked down, the type
> of CoCo Floppy Disk Controllers needs to be addressed. Both Tandy
> FDC paks are for the most identical from the software point of view.
> But there are third party devices with a few changes here and there.
> The question is, are they compatible (on the software) to the Tandy
> FDC pak. If not, what changes would I need to support to make
> software designed for them to work on FDC emulator?
> 
> The next item is the drive select lines. The standard Tandy setup
> uses 4 drive select lines to select drives 0 to 3. There was also a
> semi-standard of using drive 4 select line as the head select line
> for double sided drives. Are there any other configurations for the
> Drive Select lines than these two?
> 
> Thank you for your input,
> 
> Steve Bjork
> 
> 
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