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From: pete@stc.UUCP
Newsgroups: net.micro.cpm
Subject: Where's the DMA Address?
Message-ID: <647@stc-b.stc.UUCP>
Date: Fri, 18-Oct-85 05:00:24 EDT
Article-I.D.: stc-b.647
Posted: Fri Oct 18 05:00:24 1985
Date-Received: Mon, 21-Oct-85 06:02:43 EDT
Organization: STC Telecoms, London N11 1HB.
Lines: 34
Xpath: stc stc-b stc-b stc-a


        Put briefly, I need to know how I can find the address of
        the current DMA area.

        Expansion:

        I'm running CP/M-80 Ver. 2.2. This enables me to set the DMA to
        anywhere I like; fair enough, there's a system call for it
        (26). But I can't find any way to set it back to what it was
        before, only the default at 80H.

        The reason I want to do this is that I'm designing a print
        spooler for my home system, a Gemini Multi-Board system,
        using an area in my RAM-disk for the spool file(s) and
        interrupts from a real-time clock to drive the despooling.
        Now, sooner or later my interrupt routine is going to want
        to read a sector from the RAM-disk when an application
        program has set the DMA address to somewhere other than the
        default area. If I restore the DMA address from that used by
        the despooler to the default - Blooey!!

        I can't find this data in my Digital Research manuals.

        Any help would be very welcome.

        If there is a lot of interest, I'll summarise to the net.

        Many thanks,
-- 
	Peter Kendell <pete@stc.UUCP>

	...mcvax!ukc!stc!pete

	'Only too far is far enough'