User`s manual

STOC USER’S MANUAL ©2005 VIDERE DESIGN
In sending video information over the IEEE 1394 bus, the STOC device
uses 16 bits/pixel: 8 bits/pixel for the left image, and 8 bits/pixel for the
disparity image (default mode). Thus, the disparity image must be
compressed. For the first implementation of the STOC, the lower two bits
are truncated. Future implementations will use companding (lower values
are preserved, higher values are compressed) and 24 bit/pixel IEEE 1394
modes.
3.4 50 Hz Operation
Indoor lighting, especially from fluorescent fixtures, can oscillate at the
frequency of the electrical supply. If the image frame rate does not divide
evenly into this frequency, there can be moving horizontal bands of
alternating light and dark moving in the output.
For countries with 60 Hz power such as the United State, the frame rates in
the third column of Error! Reference source not found. are ideal. In
many other countries, the electrical line frequency is 50 Hz. For these
countries, there is a mode to change the frame rates of the STOC to sub-
multiples of 50 Hz. These frame rates are shown in the last column of
Error! Reference source not found..
The frame rate mode of the STOC device can be changed by using the
Firmware Parameter dialog – see Section
7.7.
3.5 Multiple Devices
Multiple STOC devices can be attached to the same IEEE 1394 bus. When
streaming video at the same frame rate, they are synchronized, so that they
capture images at the same time.
Each IEEE 1394 PC Card or PCI Card defines a separate IEEE 1394 bus.
The two or three ports on the card all belong to the same bus, as does any
IEEE 1394 hub connected to these ports. Separate PC Cards and PCI Cards
cannot be connected to each other.
The number of devices that can simultaneously send video is determined by
the maximum bandwidth of the bus for isochronous transfers: 32 MB/s.
This rate cannot be exceeded by the combined video streams on the bus.
Table 3 shows the bandwidth requirements for the STOC in various modes
and for various frame rates. Using this table, it is possible to determine the
maximum number devices that can stream video simultaneously. For
example, at 15 Hz and 640x480 resolution, a maximum of 3 STOC devices
can send video information at the same time.
The bus bandwidth consumed by a device is more than would be expected
from just counting the number of bytes in each frame, because there are
blank cycles on the bus, when no data is being transmitted, even though the
bandwidth is reserved. Thus, it makes no difference whether the rate is 30
Hz or 25 Hz, the bus bandwidth consumed is the same.
Frame
size
Bus MB per
frame -
stereo
30 / 25
Hz
15 / 12.5
Hz
7.5 / 6.25
Hz
3.75 /
3.125 Hz
640x480 0.683 MB 20.5 MB 10.2 MB 5.12 MB N/A
320x240 0.171 5.12 MB 2.56 MB 1.28 MB N/A
Table 3 Bus bandwidth requirements at different frame rates.
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