Re: Apple floppy adaptor. I'm stuck!

["Michael J. Mahon" <mjmahon@aol.com>]

Tristan Mumford wrote:
> Michael J. Mahon wrote:
>
>
> > Tristan Mumford wrote:

<snip>

> > > By the way. The slow stepping gives the PC floppy that satisfying "GRONK"
> > > sound of the apple drives.
> >
> > The Apple stepping algorithm is much more sophisticated than the PC's.
> > It accelerates and decelerates the stepping rather than just stepping
> > at a constant rate, reducing the total time to seek.  (Of course, the
> > time constants were chosen for a Shugart Associates SA390, so the
> > software seek could be speeded up quite a bit for newer drives.)
>
>
> When I was looking at the head stepping routines I was quite pleased
> noticing the acceleration/deceleration.
> Yeah, it could be sped up a lot. But given everything else, why bother? A
> speed increase at the cost of compatibility.

There's really no compatibility issue unless you plan to mix types
of floppies on Disk ][ Controllers on your system.

The simplest form of the patch is a single-byte change to a built-in
delay routine.  For DOS 3.3, that's all it took to make all the seeking
and wait times about 40% of what they were.  All disk operations were
sped up (except data transfer), and, since the disk was fast enough,
all the data was just where it was supposed to be--so the disks were
perfectly interchangeable.

But that must not be a big consideration for you, since the disks
you write will be readable only by your drive.

> Judging by the function of the stepping routines and the breakdown of the
> method of stepping in UTA2, I would say I am properly decoding all normal
> states of the step phase lines. However if there is other software that
> forces it to activate other combinations it will just consider that an
> illegal combination, do nothing and happily aid in destroying the contents
> of the disk :)

Sounds fair.  ;-)

> > > Another possibility I guess is that I have some kind of weird error in
> > > the head movement causing it to move to the wrong tracks.
> > >
> > > Is there some kind of low level format that I can do on an apple floppy.
> > > I tried the ProDOS format, but it looks like it only does track 0,
> > > somewhere in the middle, and track35? I just got that from watching the
> > > head movements.
> >
> > Then there is something wrong with the head movements, because both DOS
> > and ProDOS format all 35 tracks, starting with track 0.
>
>
> Hmm... I'll have to give it another good looking over. I'm going to change
> the names of a couple of the "#define" directives in my code for
> readability as it is. Ie change my "UP" and "DOWN" to "IN" and "OUT" for
> head direction reference. I suspect that I have a case of double
> backwardsness, causing the head to step in the right direction but the
> filtering logic not to work right.
>   
>
> > > I'm hoping I can get this issue sorted, because it's nearly done! I hope
> > > I can get it working right, because I actually decided to use a
> > > calculator to figure out final storage capacity *Gasp!*. A 2HD disk
> > > should hold 640kb. In it's current form a normal 2HD disk appears as one
> > > big single-sided 160 track disk.
> >
> > Several places in the Disk ][ driver/RWTS think that a disk has at most
> > 40 or so tracks--like recalibration.
>
>
> D'oh! I wonder what I can do about that. Because I have ultimate control of
> the head I guess I could make a single floppy into 4 x semi-virtual 40
> track drives. The uC keeps track of the trackcount, direction, and side of
> disk so it shouldn't be too hard at all.

It shouldn't be too hard to find out where the "seek out xx tracks"
constant is--though it may be an immediate in a few places...

-michael

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