Path: utzoo!attcan!uunet!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Newsgroups: comp.sys.amiga
Subject: Re: low level drive access
Summary: Drive select needed?
Keywords: icky direct hardware frobnication
Message-ID: <5292@cbmvax.UUCP>
Date: 22 Nov 88 04:06:30 GMT
References: <3593@crash.cts.com>
Reply-To: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Organization: Commodore Technology, West Chester, PA
Lines: 40

In article <3593@crash.cts.com> steelie@pro-charlotte.cts.com (Jim Howard) writes:
>Everyone, please refrain from flaming me!  I know direct
>hardware "hacks" tend to get frowned upon...

Ok, flame withheld, but you'd better have a darn good reason...  :-)

>Im attempting to simply move the disk head 1 track toward
>the center of the spindle.. Here's how Im doing it..
> 
>    bclr  #1,$bfd100
>**  ^^specify direction
> 
>    bclr  #7,$bfd100          ;turn on the motor
>    bclr  #0,$bfd100          ;first half of step pulse
>    bset  #0,$bfd100          ;second half of step pulse

Did you select a drive?  Something like (pardon my C):
	ACIAB->prb |= 0x78;		/* Unselect all drives */
	ACIAB->prb &= ~0x80;		/* Turn on the motor (if desired) */
	ACIAB->prb &= (0x08<<drivenum);	/* Select the one we want */
	ACIAB->prb &= ~0x02;		/* Specify direction */
	ACIAB->prb &= ~0x01;		/* First half of step pulse */
	ACIAB->prb |= 0x01;		/* Second half of step pulse */

I think I have the order correct, but I'm sure someone will correct
me if I don't.

>Now, why doesnt this do anything?  Im not exactly sure whether
>I am supposed to set up all the bits, and turn on the disk DMA,

Ouch!  (DMA is for the actual transfer of bits to/from memory, and
you'd better tell it where to start reading and writing before you
activate DMA).
-- 
					-=] Ford [=-

"The number of Unix installations	(In Real Life:  Mike Ditto)
has grown to 10, with more expected."	ford@kenobi.cts.com
- The Unix Programmer's Manual,		...!sdcsvax!crash!elgar!ford
  2nd Edition, June, 1972.		ditto@cbmvax.commodore.com