The Processor Simulator

I came across this blogspot, and I wanted to simulate the physical processor in Java, mostly because I just wanted to refresh my Computer Organization knowledge.

Why Java? Many would find it absurd to write processor simulator in Java, while writing it in C or C++ somewhat sane (the blogspot author implemented in C++). I think there is not any diference (at least, as of now), and it's a simulator, so probably doesn't matter. I indeed came across some issues like Java doesn't support unsigned integers etc but I think it doesn't matter. Will see if I need to change the language in the future.

Also, I used maven for packaging, I didn't wanted to bog down by other complexities, I just wanted to focus on simulation rather than anything else.

Op codes

Currently the processor following operations

• LOAD0:

  This is two byte instruction, where first byte is opcode 1 followed by a memory location. This loads contents in memory location in register0.

• LOAD1:

  This is same as LOAD0 but just loads the content in register1

• ADD

  This is one byte opcode. This opcode adds content of register0 and register1 and stores it into register0

• STORE

  This is two byte opcode. This stores the content of register0 into memory location given in second byte

• PRINT

  Now, this one would be really weird opcode but have this to look into a memory. This one is two byte opcode, second byte represents memory from which content would be loaded into register0 and printed to the stdout.

• HALT

  This tells CPU that program is complete.

Example programs

Program to add two numbers and print to the screen

 1;         // LOAD0        <- 1 is opcode for LOAD0
 11;        // 11           <- 11 is data
 2;         // LOAD1        <- 2 is opcode for LOAD1 
 22;        // 22           <- 22 is data
 3;         // ADD
 4;         // STORE
 6;         // 6            <- address where result is stored
 5;         // PRINT
 6;         // 6            <- address from where result should be printed
 0;         // HALT