CPUemu

CPUemu is a CPU emulator based on the MC68000. The emulator is capable of executing simple programs and show their results.

• Project structure
• Instruction's format
• Working instructions
• Program examples
• Contributing

Project structure

These are the main classes of the system with a brief description:

• CPU - Contains all the CPU registers and methods to manipulate them.
• Memory - A simulated RAM with a fixed size and accessor methods.
• Sim - The emulated system. Contains instances of CPU and Memory.
• InstructionSet - Contains all the possible instructions the CPU can execute.
• Compiler - A simple compiler that parses instructions and writes them to memory.

There are other utility classes : Utils and Costants.

Instruction's format

As of version 0.1 the instruction format is as follows:

8 bytes divided in [4 bytes for the instruction , 2 bytes for source operand , 2 bytes for desination operand] There are two kinds of instructions:

• Register-register operations (e.g: MOVE D0,D1)
• Immediate-register operations (e.g: MOVE 12,D1)

Register-register operations are transformed as follows:

MOVE -> MOVR

ADD -> ADDR

Immediate-register operations are transformed as follows:

MOVE -> MOVI

ADD -> ADDI

This is an example of how the instruction is saved onto the RAM (MOVE 5,D0):

Working instructions:

Arithmetic instructions:

• Move between Data registers (e.g : MOVE D0,D1)
• Move between Number and data register (e.g : MOVE 4,D2)
• Addition between data registers (e.g : ADD D1,D2)
• Addition between Number and data registers (e.g : ADD 4,D2)
• Subtraction between data registers (e.g : SUB D1,D2)
• Subtraction between Number and data register (e.g : SUB 5,D2)
• Multiplication between data registers (e.g : MUL D1,D2)
• Multiplication between Number and data register (e.g : MUL,D2)
• Modulo between data registers (e.g : MOD D1,D2)
• Modulo between Number and data register (e.g : MOD 5,D2)

Jump instructions:

• Branch equal (BEQ 4000)
• Branch not equal (BNE 4000)
• Inconditional Jump (JMP 4000)

Other instructions:

• Compare instructions with a register (CMP D0,D1)
• Compare instruction with an immediate operand (CMP 1000,D1)

Program examples

Program examples can be found in the programExamples folder. To load them you must reset the CPU and memory first then file->load the file.

Contributing

Feel free to contribute and to send pull requests, there are still plenty of instructions to be added and features that could be improved.