Path: utzoo!attcan!uunet!mcsun!hp4nl!phigate!ehviea!leo
From: leo@ehviea.ine.philips.nl (Leo de Wit)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Using Timer A to replay a sample
Message-ID: <892@ehviea.ine.philips.nl>
Date: 27 Sep 90 09:30:03 GMT
References: <1990Sep24.122920.15704@irscscm.UUCP> <891@ehviea.ine.philips.nl>
Reply-To: leo@ehviea.UUCP (Leo de Wit)
Organization: Philips I&E Eindhoven
Lines: 26

In article <891@ehviea.ine.philips.nl> leo@ehviea.UUCP (Leo de Wit) writes:
|Your do_snd routine must be coded as an interrupt routine; that is, it
|must end in a rte instruction; not only that, it must also mark
|(clear?) a bit in the I/O range (sorry, have to look this up),

The sequence for timer A is (I looked it up):

my_timint
    ... do your stuff here ...
    bclr #5,$fffa0f
    rte

The documentation I have says that in order to clear a bit in a MFP
register, you have to write 1's into the other bits; this is in
contradiction with the above (which is analogous to the ROM code). The
bclr instruction to memory does both read and write a byte (correct me
if I'm wrong), but this does not guarantee that 1's are written to the
other bits (they must have been there already).

The explanation for this instruction was something like: the 68K
notifies the MFP that interrupts may be delivered; I wonder what
happens if one is being delivered before the rte (this is theoretically
possible, and my spurious interrupt problem seems to indicate
practically too).

    Leo.