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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: ALSO seeking DMA peripheral controller example!
Message-ID: <20669@cbmvax.commodore.com>
Date: 15 Apr 91 22:21:53 GMT
References: <1991Apr5.110637.1@happy.colorado.edu> <1991Apr6.144654.10699@grebyn.com>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 31

In article <1991Apr6.144654.10699@grebyn.com> ckp@grebyn.com (Checkpoint Technologies) writes:
>In article <1991Apr5.110637.1@happy.colorado.edu> kskelm@happy.colorado.edu writes:
>>     It seems like I read somewhere in the docs that one should NOT take
>>over the bus [for any length of time?].  

>"Should not" is really in the light of being a good neighbor.  There's
>nothing in the Amiga system that I've seen that gets hurt if you keep
>the bus permanently, except that no further work gets done.

You can miss interrupts if you keep the bus too long.  Ideally, anything that
needs immediate interrupt response has an IOP to manage it, but that's not 
always true in practice.  The on-board serial port and some of the Zorro II
bus serial ports need pretty regular interrupt servicing or they fail.

>Most DMA hard drive adapters (significant exception: A2090A) must
>tolerate being unable to get on the bus for LONG periods, because of the
>chip RAM contention thing.  And the motherboard has no logic for timing
>out a takeover and throwing you off (this might have changed for the A3000,
>I'm not sure).

There's nothing you can legally do to throw a Zorro II bus master off the
bus, even if it's being a hog.  So we recommend that Zorro II bus masters don't
act like hogs.  A Zorro III bus master gets time scheduled for it by the bus
master, and can be gated on or off on a cycle by cycle basis.  

>First comes the logo: C H E C K P O I N T  T E C H N O L O G I E S      / /  

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      "That's me in the corner, that's me in the spotlight" -R.E.M.