From owner-freebsd-hackers Mon Aug 21 10:22:33 1995 Return-Path: hackers-owner Received: (from majordom@localhost) by freefall.FreeBSD.org (8.6.11/8.6.6) id KAA01155 for hackers-outgoing; Mon, 21 Aug 1995 10:22:33 -0700 Received: from irz301.inf.tu-dresden.de (irz301.inf.tu-dresden.de [141.76.1.11]) by freefall.FreeBSD.org (8.6.11/8.6.6) with SMTP id KAA01113 for ; Mon, 21 Aug 1995 10:22:24 -0700 Received: from sax.sax.de by irz301.inf.tu-dresden.de with SMTP (5.67b+/DEC-Ultrix/4.3) id AA03645; Mon, 21 Aug 1995 19:22:18 +0200 Received: by sax.sax.de (8.6.11/8.6.12-s1) with UUCP id TAA23873 for freebsd-hackers@freebsd.org; Mon, 21 Aug 1995 19:22:18 +0200 Received: (from j@localhost) by uriah.heep.sax.de (8.6.11/8.6.9) id TAA06361 for freebsd-hackers@freebsd.org; Mon, 21 Aug 1995 19:10:28 +0200 From: J Wunsch Message-Id: <199508211710.TAA06361@uriah.heep.sax.de> Subject: Re: How to abort a DMA transfer ? To: freebsd-hackers@freebsd.org Date: Mon, 21 Aug 1995 19:10:28 +0200 (MET DST) Reply-To: freebsd-hackers@freebsd.org In-Reply-To: <199508211340.XAA23788@genesis.atrad.adelaide.edu.au> from "Michael Smith" at Aug 21, 95 11:10:41 pm Reply-To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) X-Phone: +49-351-2012 669 X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Content-Length: 1076 Sender: hackers-owner@freebsd.org Precedence: bulk As Michael Smith wrote: > > If the scanner is using the old Omron mechanism, or a compatible, data is > only sent to the interface, and thus the DMAC, as the user moves the scanner > (clocked via an encoder driven off a roller). If the user stops moving the > scanner before the intended number of lines have been read, there's > no way for anything on that side to know. Either the driver can time out > and cancel the transfer, or it can wait 'till a new one is requested. Not an ideal basis for using DMA transfers. > Personally, I'd try to run the card on interrupt (if it generates one) - > my general opinion of the PC's DMA implementation is not flattering 8) It's an ugly crock, and the only reason the floppy driver is stuck with using it is that the hardware design essentially requires to transfer the floppy data via DMA. (PIO is unacceptable, and per-byte interrupts are neither supported nor extremely useful.) -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ Never trust an operating system you don't have sources for. ;-)