[Coco] Connect CoCo Floppy drive to Windows PC

[Steven Hirsch]

On Sun, 18 Jan 2009, Gene Heskett wrote:

> On Sunday 18 January 2009, Bill Barnes wrote:
>> IIRC, the PC Floppy controller is "sleeping" because when they designed it,
>> they designed the supporting structure to reset the FDC chip every time the
>> sector 0 sync hole came along. The CoCo didn't do that. Because of this
>> there is an unused gap between the sync and chip "reset" recovery before it
>> can write or read to the disk. It's in that gap, where the CoCo writes
>> because it isn't clobbered over the head every sync to reset, that the PCs
>> have a difficult time reading or writing to a CoCo disk that was formatted
>> on a CoCo. Formatting a CoCo disk on the PC eliminates the unreadable time
>> frame, as far as the PC is concerned, and the CoCo could care less that
>> that gap exists.
>>
> I had heard there was a gap timing problem occasionally, and it has bothered
> the coco.  But this is the first time I've read a cogent explanation of it.
> Thank you.

I'll add to that.  It's something I've noticed when moving disks back and 
forth.  Once it's been formatted on a CoCo, my Linux box chokes on it. 
Other way around works fine.


> FWIW Bill, I find that when I am doing nitros9 disk images here in this linux
> box, Fedora 8, generic kernel local build, that I must first format the disk
> on the coco in order for it to work correctly, otherwise dd gets a tummy ache
> a few sectors into the write and dumps out.  If anyone knows the secret of
> properly formatting a coco disk on linux, I would appreciate a hand.
> Software to use, command line to use, etc, please.

Exactly the opposite from my experience.  I _can_ tell you that the disk 
parms are incorrect on many systems.  Here's what I had to do on a Xubuntu 
7.04 box:

Install 'fdutils'

Check the media descriptor in /etc/mediaprm.  On my box, COCO360 and 
COCO720 used an extraneous 'zero-based' flag.  This is certainly incorrect 
for 5.25" diskettes (haven't tried the 3.5 yet).

Run the 'floppymeter' utility with a scratch diskette and let it calibrate 
for any variance in drive speed (creates a control file called 
/etc/driveprm.

Format diskettes by:

- Insert diskette in drive

$ setfdprm /dev/fd0 COCO360

$ superformat /dev/fd0 COCO360

Copy image:

$ dd if=<image_file> of=/dev/fd0 bs=256

Adjust names to suit your system.  The important issue to always execute 
setfdprm with the target disk in the drive.

Steve


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