Minimig+USB floppy drive question?

[kvasir]

I had a question about Minimig, and was hoping somebody more familiar with the hardware involved would be able to answer. I have an old USB-base external floppy drive, and was wondering if a custom USB port could be adapted to the Minimig for floppy access? I know that Amiga floppies have 2 "zones" on them, because of a variable speed on the read/write head. I'm not too familiar with standard USB floppy control, and don't know if it would be possible to either adjust the USB floppy drives read/write speed or even the disk motor speed at the sector that the Amiga disk's magnetic media would change "density"? And if USB offers that kind of control, a DD or HD Amiga floppy were could be read directly as DF0:, instead of (from what I understand) a .adf file from a SD card?

[boing4000]

That could (in theory) work. First you (or someone else) have to create an USB Port in Verlog and implement it into the Amiga hardware. Then this USB Port has to be adapted as an Amiga floppy port and then the data stream has to be synchronized.
In that case DD and HD floppy disks could be used due to the internal adaption to the different ports.

USB just need 2 wires and Spare-I/O offers it. +5V to supply the external USB Floppy will be gain directly from the power plug.

To be honest I can not do that by myself. If some developers would work together, it may be possible.

[beller]

I'd personnally rather see development time spent implementing a second virtual drive for the Minimig.  In order to run the bouncing ball demo, for example, I've got to do a shuffle of the .adf files since it's not on my worbench disk....

Hopefully someone is already working on this!

Bob

[Oli_hd]

Just a FYI the LS120 drives cant read Amiga floppies when on an Amiga, only PC 720kb/1.4Mb disks (and LS120's) so I would think a normal PC usb floppy drive would have the same problem. I think its something to do with sector sizes but have never read up on it.

[amigadave]

USB on the MiniMig has been discussed here before and IIRC it was explained that the code to implement USB in the MiniMig's FPGA would not fit.  I also think there were other reasons it could not be done, but don't remember the details of the argument.

[freqmax]

I have digged deeply into the intrisics of "USB-floppydrives" some years ago. They are completly rigid, and can't read anything but standard PC-floppies. Unless you replace their ASIC controller chip.

Electrical wise it's possible to hack some I/O ports on the Minimig FPGA (Spartan-3 XC3S400) to act as an USB port.
Software wise it would require some serious HDL-coding better spent on fixing the blitter. And take precious space from other software code needed.

So reading Amiga floppies by any density with USB-floppydrive is a dead end. Unless you want to do some serious hardware engineering.

Amiga uses more sectors per track. Different sector gap aswell I think. And possible different sync bits. Add to that the PC floppy controllers are really braindead. So they aren't flexible enough to do any efficient reading of Amiga floppydiscs.

An easier approach is infact to just wire the RD+GND pins from the floppy to the FPGA and level convert from 5V to 3.3V! Then you can just modify the Minimig floppy code to take it's MFM input from a real device.

[kvasir]

Interesting that, wasn't sure what would be required to adapt the usb floppy. Looks like more effort than its worth, though I also have an external Amiga DD floppy drive, A1000 vintage. (It has the color checkmark logo on it, even), might be easier to rig that up. The usb idea was a bit more attractive to me due to the external USB floppy drive I originally bought for my laptop is really slim, and more portable than the old A1000 drive. Another about the USB drive, though. Would it be possible to burn another ffpga or flash rom to replace this ASIC controller chip, or is this not standard enough to be worthwhile?

[tokyoracer]

Best question i'v ever seen on the Minimig subject. If it can/does have that support I think I will be looking into one myself.

[Oli_hd]

Would it be possible to burn another ffpga or flash rom to replace this ASIC controller chip, or is this not standard enough to be worthwhile?

The key thing about the minimig is its code is available so you could put it on any make of FPGA you wanted. (or even CPLD although it would be a bigger CPLD than Ive ever seen, it would need thousands of microcells)

The only problem is larger chips are normally BGA (they have solder balls under the chip that act as legs) which cant be soldered by most home DIY'ers so you would need either a developers board made by the FPGA company or to get a design made for you.

As for making it an ASIC I would think that was a bad idea as when a revised minimig core comes out you would need to make a new chip. :-/

[freqmax]

Two quick solutions:
1) Rewire with a cable capable of connecting RD, Step, Head, etc.. Then connect this to the spare I/O of the Minimig or similar.

2) Buy an FPGA-on-USB-stick. And program it with proper code. And wire it instead of the original controller.

Pay attention to 3.3V vs 5V issues thoe.