9.2.5 ALU Instructions
Having talked about the storage resources provided by the Beta ISA, let's design the Beta instructions themselves. This might be a good time to print a copy of the handout called the "Summary of Beta Instruction Formats" so you'll have it for handy reference. The Beta has three types of instructions: compute instructions that perform arithmetic and logic operations on register values, load and store instructions that access values in main memory, and branch instructions that change the value of the program counter. We'll discuss each class of instructions in turn. In the Beta ISA, all the instruction encodings are the same size: each instruction is encoded in 32 bits and hence occupies exactly one 32-bit word in main memory. This instruction encoding leads to simpler control-unit logic for decoding instructions. And computing the next value of the program counter is very simple: for most instructions, the next instruction can be found in the followin...