Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

132 Chapter 10
We need to check every time step to see if the physical buffer contention
constraints are satisfied. But the physical buffer status changes only at the
start or finish time of communication. Thus, we can reduce the number of
inequalities by checking buffer status only at the start or finish time of communication.
3.3. Heuristic algorithm
Considering that ILP belongs to the class of NP-complete problems, we devise
a heuristic algorithm based on list scheduling, which is one of the most popular
scheduling algorithms. The scheduling is a function of ETG = G(V, E) and a,
where a is a set of resource constraints. Just like the ILP formulation, it
considers physical buffers as one of the shared resources. The algorithm
consists of four steps. 1) For each shared resource, a set of the candidate nodes
(that can run on the resource) and a set of unfinished nodes (that are using
the resource) are determined. 2) For each shared resource, if there is available
resource capacity (e.g. idle processor or when the shared physical buffer
is not full), the algorithm selects a node with the highest priority among the
candidate nodes, where the priority of a node is determined by the longest
path from the candidate node to the sink node. 3) It schedules the nodes
selected in step 2. 4) It repeats steps 1 to 3 until all the nodes are scheduled.
Figure 10-3 shows the scheduling algorithm.
4. EXPERIMENTAL RESULTS
This section consists of two parts. In the first part we show the effectiveness
of the proposed approach in terms of runtime and accuracy for the H.263
example by comparing it with the simulation approach. In the second part,
we show the effect of buffer size on the execution cycles and the accuracy of