Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!rphroy!caen!hellgate.utah.edu!csn!ub!dsinc!bagate!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Direct hardware drive access
Message-ID: <20215@cbmvax.commodore.com>
Date: 31 Mar 91 08:42:25 GMT
References: <2147@pdxgate.UUCP> <mykes.0840@amiga0.SF-Bay.ORG>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 89

In article <mykes.0840@amiga0.SF-Bay.ORG> mykes@amiga0.SF-Bay.ORG (Mike Schwartz) writes:
>	bsr	StepDelay
>	rts
>You can use
>	bra	StepDelay
>Which saves 34 clock cycles and 2 bytes.

	One of the oldest optimizations known to mankind (and compilers with
tail-recursion/etc optimizations will do this too - even a simple peephole
optimizer can catch this).

>; Turn Amiga drive motor on:
>MotorOn	clr.l	tdError
>		lea	CIAB,a0
>		move.b	#%11111111,(a0)
>		move.b	#%01111111,(a0)
>		move.b	#%01000111,d0
>		or.b	tdDriveBits,d0
>		move.b	d0,(a0)
>	; wait for disk to come up to speed
>		move.l	d4,-(sp)
>		move.w	#750/3,d4
>.wait		bsr	StepDelay
>		dbra	d4,.wait

	First, the persons code you replied to was far better than this.
You're waiting .75 seconds (750 ms) on every motor-on.  We spec that floppy
drives on the Amiga MUST be up to speed in .5 seconds.  Also, the disk hardware
as a ready signal, to tell you when it's up to speed.  Many drives come up to
speed far faster than .5 seconds, or may have just been turned off and are
still close to speed, etc, or may have been on already, etc.  The person who
you responded to looped checking dskrdy.  The best way to to wait .5 seconds,
checking dskrdy every so often (2.0 trackdisk checks it every .1 seconds).

>		move.l	(sp)+,d4
>		move.l	tdError,d0
>		rts
>
>; Turn Amiga drive motor off:
>MotorOff	move.l	#CIAB,a0
>		move.b	#%11111111,(a0)
>		move.b	#%10000111,(a0)
>		move.b	#%11111111,(a0)
		^^^^^^^^^^^^^^^^^^^^  not needed, doesn't hurt
BTW, you could have coded that routine 2 bytes shorter and 12 cycles shorter,
if you care so much about space/speed.

>		rts
...
>; Step toward track 80:
>StepRight	move.l	#CIAB,a0
>		move.b	#%01000111,d0
			   ^		Interesting, that's DSKSEL3
					Ever test this code with 4 drives?
			        ^	Interesting, that's outwards (toward 0)
					This stuff of CIAB is not needed.
					(though a different one is)
>		or.b	tdDriveBits,d0
>		move.b	d0,(a0)
>		move.b	#%01000100,d0
			   ^		Interesting, that's DSKSEL3
				^	Interesting, that's inwards (toward 80)
The hardware manual says DSKDIREC MUST be set correctly BEFORE step is set to
0.  You must be lucky not to have hit a drive that actually requires it yet.

>		or.b	tdDriveBits,d0
>		move.b	d0,(a0)
>		move.b	#%01000101,d0
			   ^		Interesting, that's DSKSEL3
>		or.b	tdDriveBits,d0
>		move.b	d0,(a0)
>		move.b	#%01000111,d0
			   ^		Interesting, that's DSKSEL3
				^	Interesting, that's outwards again
					This stuff of CIAB is not needed.
>		or.b	tdDriveBits,d0
>		move.b	d0,(a0)
>		bra	StepDelay

	And where is your settle routine?  (I suspect you merely didn't
include it - you need 15ms settle after finishing seeking (on top of the
step delay!)

-- 
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")  ;-)