Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Direct hardware drive access
Message-ID: <20211@cbmvax.commodore.com>
Date: 31 Mar 91 04:36:22 GMT
References: <2147@pdxgate.UUCP>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 48

In article <2147@pdxgate.UUCP> bairds@eecs.cs.pdx.edu (Shawn L. Baird) writes:
>With the recent flamage/discussion I've revitalized some of my interest
>in trying my hand at direct disk reading. I've included a small snippet
>of code and will say that I can't even get the drive light to come on.
>The code enters with Disable() having been called and all DMA turned
>off (I'm not using any disk DMA for stepping out to track 0, so this
>shouldn't be a problem should it?). The goal is to step the disk out to
>track 0.

	I assume you've taken over the machine, or you've called GetUnit()
to obtain control of the disk hardware.

>		; step to the outside of the disk in drive 0 (I wish)
>		and.b	#$7f,ciaaprb		; select motor

	I would use #~CIAF_DSKMOTOR, that way you don't have to remember
the value of 15 million hardware bits.

>		and.b	#$f7,ciaaprb		; select drive 0

	This should be #~(CIAF_DSKMOTOR!CIAF_DSKSEL0) - you're in a timing
race to see if dskmotor goes high before the disk notices it has been selected.

>diskready:	btst.b	#5,ciaapra		; check DSKRDY
>		beq.s	diskready
>		or.b	#$02,ciaaprb		; set step direction
>checktrack0:	move.l	#3000,d0

	For safety when doing calibrates, we usually use 4ms.

>		jsr	wait
>		btst.b	#4,ciaapra		; check DSKTRACK0
>		bne.s	disktrack0
>		and.b	#$fe,ciaaprb		; step out
>		or.b	#$01,ciaaprb
>		bra.s	checktrack0
>disktrack0:	or.b	#$88,ciaaprb		; unselect drive 0

	If track 0 is set when you go into calibration, you must step in until
the track-0 indication goes away, delay a settle time (15ms on top of the
4ms step), and then reverse direction and search for track 0).

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
Thus spake the Master Ninjei: "To program a million-line operating system
is easy, to change a man's temperament is more difficult."
(From "The Zen of Programming")  ;-)