[Coco] Re: Floppy drive/OS9 issue

[Carey Eugene]

Andrew;

> Something that I am trying to understand, though: Joel, you said that
> RSDOS/Disk BASIC was never updated to use double-sided drives. I could
> have sworn, though, that with the FD502 disk system this was the case? I
> had a friend that had such a system (before I got my FD502 controller to
> replace my bad FD501 controller), and I could have sworn that with the
> drive he had you could put in a double-sided floppy, issue a DRIVE 1
> command, and read/write the other side? Maybe I am just not remembering
> things right? I am wondering if my memory is faulty, or if its a
> hardware/software issue?

You can do that with the fd-502.  Just a simple patch.  I've got a few
programs in the disks I sent you that can do that.  (Actually, most of those
programs are probably for the CC2 and will copy the roms, overwriting the
existing patched cc3 rom image.  Since the CC3 already has the rom in ram, 
you'd just need the patch, which would be a single poke (per drive) into rom 
space, I think.)

**HOWEVER** doing that is not safe.  At least not for rsdos.

The problem is that rsdos (& programs, esp. those that talk to the rom) wont
know that drive 1 is really just the back side of drive 0.  It will think it
truely is another drive.

And therefor it will expect the drive head to stay in the same place it was
when it was last accessed.

But since drive 0 & 1 are actually the same, the head will change and you
can get garbage data.  Or worse, write garbage data.

I remember doing that long ago and damaging some files.  I learned the hard
way that it wasn't always reliable.

Oh, it seemed to work right a lot of times.  But not always.  Sometimes it
screwed up.

It's been a long time and I don't remember what types of programs caused
problems, but I definetly remember having problems and as a result, I gave
up on using the back side of disks as drive 1.

That's why I kept making 'flippy' disks and why so many of the disks I sent
you are flippies.

(Oh, another issue is that some programs bypass the coco rom and talk
directly to the floppy hardware.  For example, Deft Pascal.  As a result, it
wouldn't know anything about drive 0/1 unless you patched it too.)

Carey