From alsa-devel-owner@alsa.jcu.cz  Thu Dec 17 21:28:36 1998
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Date: Thu, 17 Dec 1998 15:25:20 -0500 (EST)
From: Kenneth Crudup <kenny@panix.com>
Message-Id: <199812172025.PAA05560@panix2.panix.com>
To: alsa-devel@alsa.jcu.cz
Subject: Re:  i'm a bit confused about PCI DMA versus Bus-Master..
Reply-To: alsa-devel@alsa.jcu.cz
Sender: alsa-devel-owner@alsa.jcu.cz
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  in a sample implementation of a dos C program for the maestro II chip,
  instead, i found the Bus-Master way to let the chip control the bus and
  go to read the memory directly.. (so i understand ;-)

Yes, that's best. With PCI, there's no "DMA" really to set up; you just
let the card do the transfers on it's own via requesting the PCI bus.

  In the "real DMA" case, i believe,  the interrupt comes at the _end_ of
  the DMA transfer.

Yes. Same with PCI "DMA". It lets you know that the transfer (which occurs
"out from under you") has finished.

  Instead, in the C source that i can browse, there is an autonomous timer
  (named BOB timer), that is programmed before the bus master transfer
  start, and raise an interrupt asynchronously (obviously before the
  playback come to the end of the buffer).

Leave that C source from ESS alone; it's confused me more than it has
helped me.

	-Kenny, still hacking on it


