More than 2 FDDs on a PC (was Archiving software)

Dave Dunfield dave04a at dunfield.com
Sat Dec 17 09:19:03 CST 2005


> BTW it's not complicated at all to support a secondary FDC (shut down the 
> primary if it's on the same DMA), the programming is the same.

ImageDisk already has an option to specify the FDC hardware address,
however I do not have a system with two controllers, so I have not gone
any further toward supporting dual FDCs. What do I need to do to "shut
down" the primary FDC - it is just a matter of setting bit 3 in the Digital
output register (See description below).

If this is the case, you could try poking this bit with a debugger, and then
running ImageDisk with an optioh of "IO=372" for the secondary controller
address. If this works, let me know and  I'll include an option to disable the
primary controller.

The documents I have describe the "Digital output register"
as:

  7 = 0 Reserved
  6 = 0 Reserved
  5 = 1 Enable drive 1 motor
  4 = 1 Enable drive 0 motor
  3 = 0 Enable diskette interupts and DMA
  2 = 0 Controller reset
  1 = 0 Reserved
  0 = 0 Select drive 0
        1 Select drive 1


>From the information you posted, I gather that the logical extension
to this is:

  7 = 1 Enable drive 3 motor
  6 = 0 Enable drive 2 motor
  5 = 1 Enable drive 1 motor
  4 = 1 Enable drive 0 motor
  3 = 0 Enable diskette interupts and DMA
  2 = 0 Controller reset
  1 = 0 Select drive 0-1        11 = Drive 3
        1 Select drive 2-3  ie:  10 = Drive 2
  0 = 0 Select drive 0-2        01 = Drive 1
        1 Select drive 1-3        00 = Drive 0

Is this correct?

Again - I do not have such a controller, so it would be very hard
for me to test and maintain the software - If I make the changes
to support this, are you (or anyone) willing to test it?

Regards,
Dave

--
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:
                http://www.parse.com/~ddunfield/museum/index.html




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