Designing Digital Computer Systems with Verilog
Using Verilog, a leading commercial hardware description language, this text describes how to specify, design, and test a complete digital system.
TABLE OF CONTENTS Designing Digital Computer Systems with Verilog
3.2: Defining the VeSPA Instruction Set
3.2 Defining the VeSPA Instruction Set
The first step in defining the instruction set for a new processor is to select the set of instructions from each of the above categories that will produce a logically complete set. Additionally, we want the instructions in this set to be simple to implement, and we typically want the smallest number of instructions necessary to efficiently execute the application programs. In the following sections, we describe the instructions we have chosen for the VeSPA instruction set as we discuss some important design decisions and trade-offs.
3.2.1 Arithmetic instructions
Determining which of all possible arithmetic instructions to include in the instruction set is typically the first step in which we are directly confronted with some important trade-offs. Not only do we need to determine which specific operations we would like to include, but we also need to determine how to specify the operands.
Specifying operands
As mentioned above, each of these instructions must specify the operation itself, the operands on which it is to operate, and the next instruction to be executed. We will assume that there is a PC to implicitly determine the next instruction to be executed. In specifying the operands, we can similarly specify them either explicitly or implicitly. If we specify each operand explicitly, each binary operation would need three fields, two fields to specify the input operands and one field for the destination operand. We can reduce the number of operand fields needed in each instruction, however, by implicitly...
Copyright D. Lilja and S. Sapatnekar 2005 under license agreement with Books24x7
