Date: Wed, 28 May 1997 06:25:41 -0400 From: Randall Hopper <rhh@ct.picker.com> To: Bernie Doehner <bad@uhf.wireless.net> Cc: multimedia@FreeBSD.ORG Subject: Re: DMA and fxtv. Message-ID: <19970528062541.49315@ct.picker.com> In-Reply-To: <Pine.BSF.3.95.970527195528.1231A-100000@uhf.wdc.net>; from Bernie Doehner on Tue, May 27, 1997 at 07:58:49PM -0400 References: <Pine.BSF.3.95.970527195528.1231A-100000@uhf.wdc.net>
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Bernie Doehner: |FINALLY getting somewhere. I just ran fxtv with the -noDirectV switch and |it was rock solid. Interactive response time was horrible, but I didn't |lose any frames, picture was sharp, and NO CRASHES. | |At least I can live with this for the time being. Good deal! If it's eating too much CPU, bump up the FRAME_TIMER_DELAY_MS setting (#define at the top of tvcapture.c). This'll slow down the rate at which the frames are grabbed from the driver buffer. Now as far as analyzing why this doesn't crash you...hmmm. It's interesting. 30fps are still being kicked out by your TV card. However, it's not remaining only on the PCI bus, blasting onto your video card directly; it's being forced into the memory bus and dumped in the driver's capture buffer. This is then being sampled periodically by fxtv, coaxed into an XImage, and tossed to the XServer that then blits it to the frame buffer. What's interesting is it seems there'd be just as much PCI traffic in both cases--even a bit more in the non-direct-video case because the occasional upstream ximage blit has to compete with the downstream video from the TV card. Something just strange about PCI-to-PCI DMA on your MB chipset or your Stealth 3D 2000 I guess. Randall
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