Re: Zip Chip programming info / disk image?

[bieling@terra.es (Jorge Chamorro Bieling)]

Linards Ticmanis <ticmanis@gmx.de> wrote:

> Jorge Chamorro Bieling wrote:
> 
> >>>> -loop to wait for data coming from the disk (*).
> >>> Doesn't have to be exact, as long as it's not too *slow*.
> >> ...except if the program in question is a nibble copier -- in that case
> >> speed does matter.
> > 
> > I thought this loop just keeps waiting for the msb bit to be set in the
> > read register. 
> > The problem with a processor that is too fast is that the loop may end
> > before the disk data got into the read register ?
> 
> No... usually the loop runs forever, until data is there.

Is that what happens when you power it up without disk ? 
(keeps waiting there forever)

But, if you boot and then remove the disk you'll get i/o errors..?
So somehow it quits instead of entering an endless loop.

> 
> > Does a nibble copier read from the disk in a different way ?
> 
> Yes... it counts iterations of this loop to determine which bytes are
> sync bytes. If the loop runs far more often than is normal, this 
> detection won't work,

I though a nibble image was the raw data, as read from the read
register:

0.- Turn on drive, move to a track, setup for reading
1.- Is msb set in the read register ? if not set goto 1
2.- Save this byte
3.- been reading long enough ? if not long enough goto 1
4.- You've read during more than a whole revolution of the disk, so
you've got all the data in this track.

More or less, that's how I thought it worked.
-- 
Jorge Chamorro Bieling