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Date:      Wed, 28 May 1997 14:37:27 -0700
From:      John-Mark Gurney <jmg@hydrogen.nike.efn.org>
To:        Randall Hopper <rhh@ct.picker.com>
Cc:        Bernie Doehner <bad@uhf.wireless.net>, multimedia@FreeBSD.ORG
Subject:   Re: DMA and fxtv.
Message-ID:  <19970528143727.32928@hydrogen.nike.efn.org>
In-Reply-To: <19970528062541.49315@ct.picker.com>; from Randall Hopper on Wed, May 28, 1997 at 06:25:41AM -0400
References:  <Pine.BSF.3.95.970527195528.1231A-100000@uhf.wdc.net> <19970528062541.49315@ct.picker.com>

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Randall Hopper scribbled this message on May 28:
> 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.

actually...  this doesn't seem to help.. and it's probably the same
reason fxtv doesn't go to sleep when the Bt848 is writing directly to
video memory...

> 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.

this is interesting to as XImage mode works for me too... maybe it's the
video card that isn't handling the stream well or being out of spec then
messing up the bus...  hmm... don't somebody on hackers/current have a
pci bus analyzer?

> 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.

hmm.. guess this points more to the video card if we can watch Ximage
video fine...

-- 
  John-Mark Gurney                          Modem/FAX: +1 541 683 6954
  Cu Networking

  Live in Peace, destroy Micro$oft, support free software, run FreeBSD



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