Sensoray 615 - Manual (Page 3)

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Introduction
Model 615 is a multifunctional video capture board. It allows simultaneous capture of JPEG
compressed full resolution images and scaled down uncompressed images from 16 video inputs at
a combined rate of close to 30 (25 for PAL/SECAM) frames per second. The board has a 16-to-4
video crosspoint switch connected to 4 image capture channels (decoders), and one JPEG
compression engine. The crosspoint switch is used to connect any 4 of 16 video input signals to
the decoders. The output of any decoder can be connected to the compression engine under
software control. While the image is compressed and written to the output buffer, a scaled down
uncompressed image is also being written to the buffer. Once the output of both compressed and
uncompressed images is complete the board is ready to capture again.
A text caption of 64 characters may be overlayed on the compressed image. The position, size,
and color of the caption are controlled through software.
The following general approach is implemented in the software. During the initialization the driver
creates 2 queues: a command queue and a buffer queue. The application puts commands in the
command queue. Each command controls the following features: whether JPEG capture is enabled
or disabled, which channel (decoder) the image is captured from, which channel of the crosspoint
video switch the selected decoder is switched to after the capture is complete, whether the caption
(text overlay) is on or off, caption color selection, interlacing mode (currently only one mode is
available). See the description of COMMAND structure below.
The driver captures the uncompressed and compressed images into a buffer (see the description of
BUFFER structure below) and puts the buffer into a buffer queue, from which the application
retrieves the completed buffers as necessary. Both queues are organized as FIFO’s (first in first
out).
The following algorithm can be implemented to poll all 16 channels in a cycle (assuming that
initially input1 is connected to channel0, input2 to channel1, input3 to channel2, and input4 to
channel3):
capture from channel0 (input1), switch channel0 to input5;
capture from channel1 (input2), switch channel1 to input6;
capture from channel2 (input3), switch channel2 to input7;
capture from channel3 (input4), switch channe3 to input8;
capture from channel0 (input5), switch channel0 to input9;
capture from channel1 (input6), switch channel1 to input10;
capture from channel2 (input7), switch channel2 to input11;
capture from channel3 (input8), switch channel3 to input12;
capture from channel0 (input9), switch channel0 to input13;
capture from channel1 (input10), switch channel1 to input14;
capture from channel2 (input11), switch channel2 to input15;
capture from channel3 (input12), switch channel3 to input16;
capture from channel0 (input13), switch channel0 to input1;
capture from channel1 (input14), switch channel1 to input2;
capture from channel2 (input15), switch channel2 to input3;
capture from channel3 (input16), switch channel3 to input4.