Today I got a new, highly demanding piece of code working in our drivers. What it does is to receive streaming video from multiple 1394 cameras using a single DMA context on the 1394 adapter. Up till now each camera would have its dedicated DMA context. Since there are only four of those on most 1394 adapters, you could only receive 4 camera video streams per adapter. If you needed more you had to install a second 1394 adapter, etc.
DMA Multiplexing was a feature that we have been talking about for years in Unibrain. It would always get pushed back in the schedule since it was considered a "complex" item. Finally we did it. Of course there is more dirty work to get done, but the tricky part is over, and the important result is that the multiplexing DMA context can really handle some serious load without flinching.
I know some people like sneak technology previews so here is a photo of one of my test PCs displaying 6 cameras using a single DMA context:
If you zoom on the actual 5MP picture (1.5MB download), low on the right side you can see the 1394 bus topology, consisting of two PCs (nodes 0 and 9), six cameras, 1 repeater (node 1) and 1 analyzer (node 3). The monitor is on the blue node (node 0).
CPU usage (37%) is pretty decent for a slightly dated single CPU system.
Of course there is no way you can verify, just by looking at the photo, that all six video streams are on a single DMA context. You'll have to trust me on that :-)
Have fun!
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