Instruction Sets Mixed - Width

A pplications written for the embedded domain must perform under the constraints of limited memory and limited energy. While these constraints have always existed, current trends, such as mobile computing and ubiquitous computing, bring more and more complex applications to the embedded domain, making performance, or speed of execution, an important factor as well. For instance, we are now able to run resource-intensive gaming and multimedia applications on handheld devices. Techniques that reduce the memory and energy consumption of programs have in general done so at the cost of performance. Simultaneously achieving small code size, low energy consumption, and high performance is a challenging task. Processors, such as the ARM and MIPS family of embedded cores, support more than one instruction set to meet these constraints. In addition to the 32-bit instruction set, they support a 16-bit instruction set. As we will explain, by using 16-bit code one can achieve code size and energy reduction at the cost of performance. Until recently, the choice between 32-bit and 16-bit code had to be made by the programmer, and is highly undesirable. In this article, we show how this task can be automated and how one can achieve the code-size and energy-saving properties of 16-bit code while simultaneously achieving performance comparable to 32-bit code. We focus on the encoding of a program’s computations. This is in contrast to the previous articles in this special section, which primarily focus on the elimination of superfluous computations from a program. The techniques described here are in the context of the ARM family of processors, which are frequently used in the embedded computing realm. They are used as general-purpose embedded processors, found, for example, on multimedia-enabled PDAs, as well as in specialized embedded applications, such as embedded control. ARM processors have a simple energy-efficient architecture. The StrongARM [8], INSTRUCTION SETS MIXED-WIDTH BY ARVIND KRISHNASWAMY AND RAJIV GUPTA