Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

State Space Compression in History 273
In the case of the MPEG example the improvements achieved when using
the hash table are spectacular. This is mainly due to the presence of many
quasi-equivalent paths.
A noteworthy aspect is that due to the employment of search heuristics to
select the next ECS to fire, the schedules obtained when using hash tables can
be different from those generated in their absence. As can be deduced from
the former tables, the number of different states in the schedule tends to be
lower when the hash table is used. Since the reachability graph needs to be
traversed by the code generation phase, this means that the obtained schedule
could potentially be more efficient and help to produce code of better quality.
6. CONCLUSIONS
In this paper we have addressed the problem of reducing the solution space
explored during quasi-static scheduling in a software synthesis methodology
for one-processor, embedded, reactive systems.
We have studied different ways to compress the state space to reduce the
size of the schedule. We have shown that the structure of the specification
PN can be examined to identify sequences of traces that could be fired at once
during the scheduling with the help of marking equations. Further, we have
shown that a scheme based on the use of efficient hash tables provides an
effective way to eliminate state repetitions.
The experimental results we have obtained demonstrate the usefulness of
our technique, yielding outstanding reductions in the CPU time and memory
consumed by the scheduling algorithm for large-scale, real world problems.
ACKNOWLEDGEMENTS
This work is partly supported by MCYT projects TIC2000-0583-C02 and
HI2001-0033.
NOTE
1
This requirement does not impose restrictions because any PN with self-loops can be transformed
into self-loop-free PN by inserting dummy transitions.
REFERENCES
l.
2.
A. V. Aho, R. Sethi and J. D. Ullman. Compilers: Principles, Techniques and Tools. Addison
Wesley, 1986.
Cortadella, J. et al. “Task Generation and Compile-Time Scheduling for Mixed Data-Control
Embedded Software.” In Design Automation Conference, pp. 489–494, 2000.