Title page for ETD etd-01262005-135906


Type of Document Master's Thesis
Author Mahapatra, Satya Swaroop
URN etd-01262005-135906
Title Heuristics for Offset Assignment in Embedded Processors
Degree Master of Science in Electrical Engineering (M.S.E.E.)
Department Electrical & Computer Engineering
Advisory Committee
Advisor Name Title
Jagannathan Ramanujam Committee Chair
Bijaya B. Karki Committee Member
Jerry L. Trahan Committee Member
Keywords
  • offset assignment
  • partitioning
  • heuristic
Date of Defense 2004-12-13
Availability unrestricted
Abstract
This thesis deals with the optimization of program size and performance in current generation embedded digital signal processors (DSPs) by the design of optimal memory layouts for data. Given the tight constraints on the size, power consumption, cost and performance of these processors, the minimization of code size in terms of the number of instructions required and the associated reduction in execution time are important. Several DSPs provide limited addressing modes and the layout of data, known as offset assignment, plays a critical role in determining the code size and performance. Even the simplest variant of the offset assignment problem is NP-complete. Research effort in this area has focused on the design, implementation and evaluation of effective heuristics for several variants of the offset assignment problem.

One of the most important factors in the determination of the size, and hence, execution time of a code is the number of instructions required to access the variables stored in the processor memory. The indirect addressing mode common in DSPs requires memory accesses to be realized through address registers that hold the address of the memory location to be accessed. The architecture provides instructions for adding to and subtracting from the values of the address registers to compute the addresses of subsequent data that need to be accessed. In addition, some DSP processors include

multiple memory banks that allow increased parallelism in memory access. Proper partitioning of variables across memory banks is critical to effectively using the increased parallelism.

The work reported in this thesis aims to evolve efficient methods for designing memory layouts under the conditions of availability of one address register (SOA) or of multiple address registers (GOA). It also proposes a novel technique for choosing the assignment of variables to the memory banks. This thesis motivates, proposes and evaluates heuristics for all these three problems. For the SOA and GOA problems, the heuristics are implemented and tested on different random sample inputs, and the results obtained are compared to those obtained by prior heuristics. In addition, this thesis provides some insight into the SOA, GOA and the variable partitioning problems.

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