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To: Thomas Roell <roell@crab.xinside.com>
cc: Randall Hopper <rhh@ct.picker.com>, multimedia@freebsd.org
Subject: Re: Bt848 driver & Wincast -- some success 
In-reply-to: Your message of "Wed, 12 Feb 1997 08:06:51 MST."
             <199702121506.IAA08268@xeno.xinside.com> 
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Date: Wed, 12 Feb 1997 13:18:27 -0800
From: Amancio Hasty <hasty@rah.star-gate.com>
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Hi,

The Bt848 can burst to different address pending on the frame . All this
controlled by a "Risc Program" which the Bt848 executes during the
video capture process.



This is a simple loop in the driver. What is doing is loading 
into physical memory : 
	"write to this address N number of pixels"
	"write to this address M number of pixels"
N+M has is the total width of pixels desired.

for even frames , I start bursting the frame data to the start of the buffer
for odd  frames , the starting addres of the capture buffer is "buffer+pitch".



    for (i = 0; i < (rows/interlace )  ; i++) {
      *dma_prog++ = inst;
      *dma_prog++ = target_buffer;
      *dma_prog++ = inst3;
      *dma_prog++ = target_buffer + b;
      target_buffer += interlace*(cols * pixel_width); 
    }

If you wanted to do double or tripe bufferring  then it will be a simple
matter of loading into the host memory and appropiate program
which starts to burts the frame at the desired address in memory
    
Where is the list of dual display capable cards ? 8)

	Cheers,
	Amancio


>From The Desk Of Thomas Roell :
> In your message of 11 February 1997 you write:
> 
> > Hi,
> > 
> > You need the B848 Databook from Brooktree if you want to hack on the
> > driver, period.
> > 
> > What is your CPU and motherboard chipset, example Natoma or Triton...
> > 
> > If you have a Mercury chipset, then you don't have enough PCI bandwith 
> > to drive a 640x480 32bits picture. Also try playing with the PCI parameters
> > in your BIOS. Your PCI clock rate should be around 32 or so and not 60 or
> > higher.
> > 
> > You can try 320x240 with something like 15bits or 8bits color depth.
> > 
> > The ghostimage that you are experiencing in your system is an indication
> > that your PCI chipset is not able to keep up with the Bt848.
> > 
> > The driver does not have the ioctls to transfer video to memory and
> > is not hard to add . I can provide this feature before the end of 
> > the week;however, if you want to take advantage of this feature
> > then you will have to ask the XFree86 team or peruse thru their 
> > release notes for an appropiate video card which supports linear
> > frame buffering.
> 
> *smile* Or Xi Graphics (the artist formerly known as ...)
> 
> Actually writing YUV422 and 320x240 makes more sence that 15bpp or
> 8bpp TrueColor. The graphics chip can do the color-space conversion.
> 
> What I'm really curious about is whether the Bt848 can do
> doublebuffering. I mean an even field into buffer A and an odd field
> into buffer B.
> 
> - Thomas
> -- 
>              Thomas Roell   /\       Ein Nasshorn und ein Trockenhorn
>              Xi Graphics   /  \/\ _    spazierten durch die Wueste,
>       roell@xinside.com   /   /  \ \    da stolperte das Trockenhorn,
>                          / Brumpft! \    und's Nasshorn sagte: "Siehste!"