Minecraft Computer

This is a fully functional general purpose programmable computer created in minecraft purely using redstone.

Specification

Registers

The computer contains a 4bit program counter and 3 separate 8bit general purpose registers.

General Purpose Registers

Register	size	usage
r0	8bits	Always set to 0. Writing to this register does nothing
r1	8bits	An general purpose register
r2	8bits	An general purpose register
r3	8bits	An general purpose register

Specialized Registers

Register	size	usage
pc	4bits	The program counter. It can be updated via the JMP instruction.

ALU

The ALU is extremely basic and can only perform addition and subtraction

I/O

The computer contains a single 8bit output port that can be written to using the DSP instruction

Instruction Set

The instruction set is extremely simple and consists of four main instructions:

Instruction	opcode	Parameters	Usage
DSP	00	OPCODE: 2bits; RESERVED: 2bits; SRC: 2bits; RESERVED: 4bits	displays the contents of the register specified by SRC
JZ	01	OPCODE: 2bits; SRC: 2bits; CONSTANT: 6bits	sets the program counter to CONSTANT if the register specified by SRC is 0 (Note: the program counter is only 4 bits wide and so the first 2bits of CONSTANT are ignored)
SET	10	OPCODE: 2bits; DST: 2bits; CONSTANT: 6bits	sets the first 6 bits of the register specified by DST to CONSTANT
ALU	11	OPCODE: 2bits; DST: 2bits; SRC1: 2bits; SRC2: 2bits; FUNC: 2bits	Performs the arithmetic operation specified by FUNC on SRC1 and SRC2, storing the output in DST

ALU INSTRUCTION

The ALU instruction has the following format:

2 bits	2 bits	2 bits	2 bits	2 bits
OPCODE	DST	SRC1	SRC2	FUNC

The alu instruction format performs DST = SRC1 FUNC SRC2 where FUNC is some arithmetic instruction specified in the below table.

FUNC	OPERATION
00	ADD
01	SUB
10	UNDEFINED
11	UNDEFINED

Example Program

The following program will output the numbers in the Fibonacci sequence until an integer overflow occurs at which point it will display the last 8bits of the rest of the Fibonacci numbers.

r1 = 0
r2 = 0
while (true)
	r3 = r1
	r1 = r2 + r3
	r2 = r3
	print(r1)

Binary	Assembly
10 01 000000	SET r1 0
10 10 000000	SET r2 0
	loop_start:
11 11 01 00 00	ADD r3 r1 r0
11 01 10 11 00	ADD r1 r2 r3
11 10 11 00 00	ADD r2 r3 r0
00 00 01 0000	DSP r1
01 00 000011	JZ r0 loop_start

TODO:

• Implement conditional jumps jl and jle. This will require increasing the opcode width and instruction width by 1
• add multiple outputs. Use the first two RESERVED bits in the display instruction to specify which port to write to.