
Philips Semiconductors
PNX15xx Series
Volume 1 of 1
Chapter 12: Video Input Processor
PNX15XX_SER_3
Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet
Rev. 3 — 17 March 2006
12-14
Capture Enable Mode
Using the
cfen bits, video capture can be limited to odd or even or both elds. If both
elds are to be captured, the capture starts with the next odd eld.
The status of the osm (one-shot) bit in the mode-control-register species the capture
mode (one-shot or continuous):
If osm=0, the corresponding incoming video stream is captured continuously. For
example, in a video conference application the vanity image would be a
continuous stream to the frame buffer.
If osm=1, the corresponding incoming video stream is captured one eld or frame
at a time (depending on the
cfen bits).
Programming hint: In a video conference application the captured image would be a
one-shot stream to the host memory. If you write osm=1 and select eld/frame in the
register, it is captured on the next VSYNC and cfen bits are cleared to 0. To capture
the next image, the cfen and osm bits must be reprogrammed.
Address Generation
The line address is generated by loading the base address from the corresponding
register set at the beginning of each eld and adding the line pitch to it at the
beginning of every new line.The lower three bits of the rst three base address
registers are used as an intra-long-word offset for the left-most pixel components of
each line. The offset has to be a multiple of the number of bytes per component.
Double Buffer Mode
To avoid line tear caused by trying to display a frame at the same time that it is being
updated, a double buffer mode is available. In this double buffer mode, a second set
of DMA base addresses is available. After capturing and storing one complete frame
in the location described by one set, the other set is used for the next frame. The idea
Figure 11: Double Buffer Mode
Frame 1
Frame 2
dma_base1
dma_base2
Odd
Even
Odd
Even
dma_base3
dma_base4