Sensoray 817 - Manual (Page 6)

6
Operation
Video capture
Model 817 contains four identical video capture and processing units (VCPU), each of
which handles 4 input video channels. Each VCPU employs a 4-channel video decoder
to convert analog video into digital, and a powerful digital signal processor (DSP) to
capture digitized video and handle various processing tasks: frame decimation, caption
overlay, JPEG compression, status reporting, etc.
The data from each DSP is sent over an internal 66 MHz 32-bit PCI bus to a PCI Express
bridge, which connects to the host computer’s PCI Express slot.
Each channel is set up independently of the others. Once the capture on a particular
channel is enabled, the required data (JPEGs and/or bitmaps, status information) is
transferred to the host using DMA, i.e. without any host’s intervention. That results in a
very low percentage of CPU time taken by capture process alone, and most of the
computing resources being available for the application software. Below is a screen
capture of the Windows Task Manager window taken while one model 817 board was
capturing at a maximum frame rate on all channels (no display of captured images,
Pentium D 2.8 GHz).