
Philips Semiconductors
Overview
PRODUCT SPECIFICATION
2-5
Figure 2-3 illustrates a possible display situation and the
data structures in SDRAM that support ICP operation.
On the left, the PC video screen has four overlapping
windows. Two, Image 1 and Image 2, are being used to
display video generated by TM1300. The right side
shows a conceptual view of SDRAM contents. Two data
structures are present, one for Image 1 and the other for
Image 2. Figure 2-3 represents a point in time during
which the ICP is displaying Image 2.
When the ICP is displaying an image (i.e., copying it from
SDRAM to a frame buffer), it maintains four pointers to
the SDRAM data structures. Three pointers locate the Y,
U, and V data arrays, the fourth locates the per-pixel oc-
clusion bit map. The Y, U, and V arrays are indexed by
source coordinates while the occlusion bit map is ac-
cessed with screen coordinates.
As the ICP generates pixels for display, it performs hori-
zontal scaling and colorspace conversion. The final RGB
pixel value is then copied to the destination address in
the screen’s frame buffer only if the corresponding bit in
the occlusion bit map is a ‘1’.
As shown in the conceptual diagram, the occlusion bit
map has a pattern of 1s and 0s corresponding to the
shape of the visible area of the destination window in the
frame buffer. When the arrangement of windows on the
PC screen changes, modifications to the occlusion bit
map is performed by TM1300 or host resident software.
It is important to note that there is no preset limit on the
number and sizes of windows that can be handled by the
ICP. The only limit is the available bandwidth. Thus, the
ICP can handle a few large windows or many small win-
dows. The ICP can sustain a transfer rate of 50 megapix-
els per second, which is more than enough to saturate
PCI when transferring images to video frame buffers.
2.5.6
Variable-Length Decoder (VLD)
The
variable-length
decoder
(VLD)
relieves
the
DSPCPU of decoding Huffman-encoded video data
streams. It can be used to help decode high bitrate
MPEG-1 and MPEG-2 video streams. The lower bitrate
of videoconferencing can be adequately handled by
DSPCPU software without coprocessor.
The VLD is a memory-to-memory coprocessor. The
DSPCPU hands the VLD a pointer to a Huffman-encod-
ed bit stream, and the VLD produces a tokenized bit
stream that is very convenient for the TM1300 image de-
compression software to use. The format of the output
token stream is optimized for the MPEG-2 decompres-
sion software so that communication between the
DSPCPU and VLD is minimized.
2.5.7
Audio In and Audio Out Units
The Audio In (AI) and Audio Out (AO) units are similar to
the video units. They connect to most serial ADC and
DAC chips, and are programmable enough to handle
most serial bit protocols. These units can transfer MSB
or LSB first and left or right channel first.
The audio sampling clock is driven by TM1300 and is
software programmable within a wide range. Like the VO
unit, AI and AO sample rates are separately and dynam-
ically programmable. The high-quality on-chip sample
clock generator circuits allows the programmer subtle
control over the sampling frequency so that audio and
video synchronization can be achieved in any system
configuration. When changing the sample frequency, the
instantaneous phase does not change, which allows
sample frequency manipulation without introducing au-
dio or video distortion.
0000000000000000
1111100000011111
1111111111111111
PC Screen
Image 1
File
Edit
Format View
File
Edit
FrameMaker 5
IMAGE 1
Calendar
In SDRAM
Image 2
Y
U
V
Y
U
V
1111111111111111111111
1111111100000011111111
Image 1
Image 2
ICP
Figure 2-3. ICP - Windows on the PC screen and data structures in SDRAM for two live video windows.