Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mit-eddie!ll-xn!ames!pasteur!ucbvax!CORY.BERKELEY.EDU!dillon
From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Interrupt Server, Parallel port
Message-ID: <8804282319.AA04553@cory.Berkeley.EDU>
Date: 28 Apr 88 23:19:52 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 30

>I understand that I will have to add an interrupt server to the chain that
>is already attached to the 8520 (called "PORTS", I think).  I have set up
>my UART to assert the "FLAG" interrupt on the 8520, but my question is,
>how do I check this bit in the interrupt register without clearing the
>whole register?  Actually, since somebody higher up in the chain (timer
>interrupts, for example) already had to check this register, it must
>*already* be cleared (it automatically clears on reading).

	Exactly.  There is *Nothing* you can do!  You can't read the
register manually because it will screw up all the other servers on
the chain, meaning that you *MUST* use FLAG as an interrupt only.

	Also, note that PC/FLAG is activated/acknowledged by a read
or write to (port B?) and you can't get around that either.

>Perhaps the PORTS server passes this register along somehow, but if it
>does, I have no way of knowing.  As far as I can tell, the system
>interrupt servers are undocumented (correct me if I'm wrong - I've got
>the original "white" manual set).

	If you set up your server to work with the FLAG interrupt, the
server will be run when a FLAG interrupt occurs.  Perhaps I am 
confused as to your use of the line.  If you want to use FLAG as a
digital input, you can't.  Also, if you are trying to receive serial
data on the line, good luck... the timing is too critical to be able
to do it with an interrupt on that chain.

>phil@eos.arc.nasa.gov

			-Matt