Re: Two concurrent floppies?

David C Niemi (niemi@wauug.erols.com)
Tue, 3 Jun 1997 22:39:44 -0400 (EDT)

>Alan Cox (alan@lxorguk.ukuu.org.uk) Tue, 3 Jun 1997 22:01:37 +0100 (BST)
>> I have (for no other reason than it looks pretty cool) two 3.5" HD
>floppy
>> drives, and it seems that I can only have one running at any given time.
>> eg. dd if=/dev/fd0 of=image0 bs=64k & dd if=/dev/fd1 of=image1 bs=64k
>> will only read from 1 drive at a time. This is obviously not a big
>> problem, and I tend only to notice when dd'ing RH install disks, but I'd
>> be interested to hear whether this is a chipset/fdc thing of a driver
>> problem.
>
>Neither the floppy controller nor the motherboard DMA can do two things
>at once. This is actually a right pain in the arse with floppy tape
>drives.

You can get some interesting results from copying floppy to floppy (cp
/dev/fd0 /dev/fd1 is sufficient). I have seen the two floppies sync up so
one reads a track while the other seeks if they are similar types. Using
bs=64k won't help anything on Linux, though, as typical floppies use 18K
sizes anyway and only on other OSes like SunOS4 do you really need to use
explicit block sizes.

As for floppy parallelism, in theory you could simultaneously use 2
floppies by putting them on separate floppy controllers at different DMA
and I/O addresses. Alain Knaff and I added support for multiple FDCs long
ago (one active at a time), but it is rarely used, and I don't think we
ever moved one over to another DMA channel. Floppies are just not that
exciting nowadays, the only application I can think of for multiple FDCs
would be some sort of low-end floppy duplicator machine.

David
Niemi@wauug.erols.com 703-810-5538 Reston, Virginia, USA
--- Wonders can be worked given enough intelligence and persistence.
--- Miracles, on the other hand, still require divine assistance.