Let’s see
640 X 480 X 4 bytes/pixel X 120 frames/second = ~400 MB/sec
Add 33% interaction overhead = 533 MB/sec
AGP 1X theoretical bandwidth = 266 MB/sec
AGP 2X theoretical bandwidth = 533 MB/sec
AGP 4X theoretical bandwidth = 1066 MB/sec
Since real systems will generally get at best about 75% of max throughput,
you need AGP 4X to even have a chance.
But it’s worse than that.
Standard AGP use has the program write data to memory and the AGP pull it
from memory. So your load against memory bandwidth is 2*533 = 1066 MB/sec.
The current best memory technology, DDR, is speced to a max throughput of
2100 MB/sec. So you’re already using half of the available memory bandwidth.
And that 2100 is a very optimistic number that assumes that every cycle
transfers payload data. In other words, it’s a peak not a sustained rate. In
a real system you also have memory refresh, address changes, precharge time,
and so on. The better PC systems will actually get 1600-1700 MB/sec so if
you pick your hardware carefully you can move the data and have some
bandwidth left over to run the CPU.
So figure you’ve got 500 MB/sec available to run the CPU and to bring your
data in from whatever the source device is.
I suspect this doesn’t work. If your source data is uncompressed it uses all
of the remaining bandwidth. If it’s compressed, you save data bandwidth but
increase the amount needed to feed instructions to the CPU.
In summary, you might get this to work on a carefully selected system, it
I’d be surprised.
Why do you need 120 frames/sec when the human eye can’t perceive much over
30 at best?
++PLS
-----Original Message-----
From: Max Paklin [mailto:xxxxx@yahoo.com]
Sent: Wednesday, February 20, 2002 7:16 PM
To: NT Developers Interest List
Subject: [ntdev] Re: How to achieve higher frame rate WDM Stream classs
mini drivers
I would guess that data rate is too high for whatever bus you push it
through. It could also be that video card performance is insufficient to
handle data rate in question.
Just in case make sure that maximal data rate you specify in
VIDEOINFO/VIDEOINFO2 format structure for corresponding stream is
sufficient to cover worst case scenario. I don’t think it’ll help though.
Max.
— “Srikanth.R.K.” wrote:
> Hi,
>
> I have developed a stream class mini driver, which talks to bus drivers
> for
> getting video data. In this case, I have a specific need in which I need
> to
> achieve upto 120 frames/second in 640x480 display mode. Till now, I am
> unable to do so. I am able to achieve around 120 frames/second ONLY in
> 160x120 video mode. As the frame size increase, the frame rate decreases
> drastically.
>
> Can anyone let me know how to achieve higher frame rate (120 frames/sec)
> in
> 640x480 video mode?
>
> Thanks
> Srikanth.R.K.
>
> —
> You are currently subscribed to ntdev as: xxxxx@yahoo.com
> To unsubscribe send a blank email to leave-ntdev-$subst(‘Recip.MemberIDChar’)@lists.osr.com
__________________________________________________
Do You Yahoo!?
Yahoo! Sports - Coverage of the 2002 Olympic Games
http://sports.yahoo.com
—
You are currently subscribed to ntdev as: xxxxx@ticketmaster.com
To unsubscribe send a blank email to leave-ntdev-$subst(‘Recip.MemberIDChar’)@lists.osr.com
—
You are currently subscribed to ntdev as: $subst(‘Recip.EmailAddr’)
To unsubscribe send a blank email to leave-ntdev-$subst(‘Recip.MemberIDChar’)@lists.osr.com