Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!nfsun!eklektik!danbabcock
From: danbabcock@eklektik.UUCP (/dev/ph1)
Newsgroups: comp.sys.amiga.tech
Subject: Disk drive ready signal/drive clicking
Message-ID: <1732@eklektik.UUCP>
Date: 10 Apr 90 21:47:31 GMT
Reply-To: danbabcock@eklektik.UUCP (/dev/ph1)
Organization: Computers, Gerbils, and Games in the Basement, Pgh, PA
Lines: 34

dannys@csd4.csd.uwm.edu wrote in <3342@uwm.edu>:

> ...I left the RDY line connected to the autoconfigure
> part of the interface circuit but not connected to any drive signals.
> Why does this work? Does software wait 500ms after motor-on before doing
> any read/writes? I would think you would wait for the RDY line to become
> active...

I would assume that the trackdisk.device waits 500ms before bothering
to check the ready line. After all, the ready line does not generate an
interrupt, so this is the most efficient method. However, almost all
custom disk code that I have seen (this includes many games and 
probably copy programs as well) uses the disk ready signal exclusively;
they just sit in a loop waiting for it to be asserted.

> What is software doing to make the drives click? (etc.)

The drives are supposed to latch the disk change signal when the drive
steps a track, so the Amiga steps the drive periodically to determine when
a disk is changed. All the code does is step one track, inverting the
direction each time. I don't recommend defeating this in hardware; it 
would probably be incompatible with many programs. There is an easy
way to defeat this in software, though - just change the code to step
in one direction instead of alternating directions. Many drives have logic
to detect when they have stepped past track zero (track zero is the
outermost track) and refuse to step further - but still latch the disk
change signal! The change may be made directly via a one-bit patch on
the kickstart disk (if you're a 1000 owner) or in EPROM (if you're a
500/2000 owner with one of those kickstart switchers) or by using
SetCPU (if you're a '020-with-MMU or '030 owner) or by using a program
such as NoClick (anyone). In fact, I wrote the first version of NoClick
(it didn't work very well, but other people fixed it up).

-- Dan Babcock / voice (412)-373-1753