[e2e] TOEs and DVDs

[David P. Reed]

The early PC DVD players used DVD decoder chips that had direct access to 
the video frame buffer.  These chips primarily accelerated two inner loop 
aspects of MPEG decoding: expanding the DCT data, and implementing the 
motion compensation (which amounted to memory-to-memory BLTs in the frame 
buffer).   The  CPU read data into primary memory buffers, then sent that 
data to the DVD decoder chips in the form of commands to do various 
operations.   Memory bandwidth was not a problem, even with early PCI buses.

There were MPEG software decoders, of course, but there was a period when 
the bulk of the installed computing base did not have sufficient processor 
power to do the work, and the video frame buffers (being dual ported 
memories) were not on a fast enough bus for the processor to read and write 
back for the motion compensation code.   The solution for cheap systems was 
to make the frame buffer access from the CPU faster (Intel did this as part 
of the sequence of changes including AGP), and the SIMD Intel architecture 
extensions were designed to do stuff like the DCT better.

Today it is still the case that DVD decoding may be offloaded, but now 
to  "3D accelerator" chips where possible, and the GPU is now a full 
vector/matrix piplelined signal processor with its own frame buffer (at 
Stanford I hear that they are using GPUs for general numerical algorithm 
acceleration).

Don't know what this has to do with a TOE, exactly.  The main point is that 
better buses and additional processors eventually evolve away from 
specialization to be general purpose resources.  There's very little reason 
to assume a task is so specialized that its acceleration can't be achieved 
as part of a more general solution.
At 02:29 PM 4/8/2004, Craig Partridge wrote:

>Hi folks:
>
>I was rethinking the TOE discussion in my head earlier this week and hit
>a question that I thought someone here might know the answer to.
>
>It seems to me that playing a DVD on a computer is a very similar problem
>to sending or receiving networking data, in the sense that typically the
>data is going from one peripheral to another with the processor mediating.
>And one of our problems is that the stuff (memory infrastructure) around
>mediating processor is slow relative to the data rates we wish to achieve
>between peripherals.
>
>Now, today, I suspect that DVD bandwidth doesn't stress a memory system.
>But it surely did a few years ago.  What did the video crowd interested
>in making general puropse computers into competent DVD players do in
>response?  Something like a TOE -- something else?
>
>Thanks!
>
>Craig
>
>E-mail: craig at aland.bbn.com or craig at bbn.com