Dynamic Dataflow Graphs - Signal Processing Systems - page 898

Fig. 4 An implementation of the switch actor design of Fig. 3 in the functional DIF environment

6.1 SADF Graphs

In this subsection SADF is introduced by some examples from the multi-media
domain. Consider the MPEG-4 video decoder for the Simple Profile from [ 66 , 70 ] .
It supports video streams consisting of intra (I) and predicted (P) frames. For an
image size of 176

144 pixels (QCIF), there are 99 macro blocks to decode for
I frames and no motion vectors. For P frames, such motion vectors determine the
new position of certain macro blocks relative to the previous frame. The number
of motion vectors and macro blocks to process for P frames ranges between 0 and
99. The MPEG-4 decoder clearly shows variations in the functionality to perform
and in the amount of data to communicate between the operations. This leads to
large fluctuations in resource requirements [ 52 ] . The order in which the different
situations occur strongly depends on the video content and is generally not periodic.
Figure 5 depicts an SADF graph for the MPEG-4 decoder in which nine different
scenarios are identified. SADF distinguishes two types of actors: kernels (solid
vertices) model the data processing parts, whereas detectors (dashed vertices)

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