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From: jcs@crash.cts.com (John Schultz)
Newsgroups: comp.sys.amiga
Subject: Re:  NoiseTracker V2.0 out!
Summary: Sounds/Interrupts
Message-ID: <3992@crash.cts.com>
Date: 18 Aug 90 16:56:52 GMT
References: <9008120043.AA03382@jade.berkeley.edu> <0oPVN2w162w@valnet.UUCP> <1990Aug17.104306.17285@gdr.bath.ac.uk>
Organization: Crash TimeSharing, El Cajon, CA
Lines: 39

In article <1990Aug17.104306.17285@gdr.bath.ac.uk> mapjilg@gdr.bath.ac.uk (J I L Gold) writes:
>One of the major uses of Soundtracker is to produce scores for demos/games
>or whatever. In order for this to work the player routine must be called in a 
>50Hz vertical blank interrupt. As far as I can make out, the MED player routine 
>functions as a separate task, and so will not work in a program where the
>system call Forbid() has been made to turn off multitasking (ie games, demos...)
>Or am I showing my ignorance again?
>Comments? Help? 

  A VBlank interrupt is not necessary, as the audio hardware generates
interrupts after the last word of data has been fetched. This allows
audio interrupts to stuff the registers with the next sound before the
first has finished. As long as DMA is not turned off, the next sound
will continue immediately after the previous sound.  See the Amiga
Hardware Manual for more info.

  On the subject of stopping sounds immediately and starting a new sound
cleanly, what's the best way to do this? Currently I do:

	move.w	d2,intena(a0)		; disable 7-10 (aud) interrupts
	move.w	d2,intreq(a0)		; clear any 7-10 interrupts

	move.w	d6,dmacon(a0)		; shut off dma for both channels
	move.w	#0,ac_dat(a3)		; write directly to output (to stop)
	move.w	#0,ac_dat(a4)		; write directly to output (to stop)
	move.w	#1,ac_per(a3)		; fast period (less waiting)
	move.w	#1,ac_per(a4)		; fast period (less waiting)
	move.w	#$c000,intena(a0)	; enable
wasteloop
	move.w	intreqr(a0),d5		; wait for interrupt
	and.w	d2,d5			; test against current mask
	beq.b	wasteloop		; not yet occurred
; Interrupt has occured, channel is stopped.
	move.w	d2,intreq(a0)		; clear two 7-10 interrupts

  Is there a better way to do this?


  John