Re: 3.5 unidisk

[dempson@actrix.gen.nz (David Empson)]

Drew <goggledrew@gmail.com> wrote:

> On 25 Feb, 17:18, "Bill Garber" <willy4...@garberstreet.com> wrote:
> > "Drew" <goggled...@gmail.com> wrote:
> > > I picked up a faulty 3.5 Unidisk and replaced the insides of it with a
> > > standard GS 3.5 drive 800k internal. All seems to work, which is good,
> > > but under GS/OS though i can format and all works the drive seems to
> > > be access every few seconds. Is this normal? Doesn't happen on my IIC
> > > and only seems to be under GS/OS. It was more out of interest
> > > really :)
> >
> > Yes, it is normal. You will also find that it happens on the IIc Desktop
> > program. Memory failing, can recall it's real name, MouseDesk?  Maybe?
> >
> > Anyway, yes, the 3.5" Unidisk is a Smartport drive, so is polled every
> > few seconds.
> 
> Ok was just odd seeing it flash every few seconds. The normal GS
> drives don't do it so wasn't sure it was normal :). Thanks for
> clearing it up Bill.

Actually the Apple 3.5 Drive _is_ polled every second in the same way.
It just happens so quickly that you barely see it. You have to be
watching the LED closely to notice it.

In the case of the Apple 3.5 Drive, GS/OS is polling the "has the disk
been changed" status flag, which requires selecting the drive via the
IWM, sending a register select command, reading an input then
deselecting.

In the case of the UniDisk 3.5, the same procedure is followed but it is
done by the processor inside the drive. The computer has to select the
UniDisk 3.5, send a command packet, then the UniDisk 3.5 sends a
response packet. This takes longer than a quick poll of an Apple 3.5
Drive. I expect the UniDisk 3.5's processor also has a "minimum
activation period" timer on its LED so it leaves the LED on longer than
necessary.

-- 
David Empson
dempson@actrix.gen.nz