Threaded Code Interpreter for Object Code
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
A method is described to simulate or emulate the functions of an older processor's instruction set with software or microcode. The simulator has two basic steps: 1. Interpret the object code of an instruction to determine its function. 2. Perform an equivalent function. Since most processors have instructions which perform similar functions, step 2 can usually be handled with one instruction or, at worst, a short sequence of instructions. In the case where the new processor has a very simple instruction set, and the old processor has a complex instruction set, simulating the functions of the commonly used instructions requires an average of 5 to 15 new instructions. Due to the complex nature of the old instruction set, however, up to 150 new instructions may be required to interpret an old instruction (step 1).