Introduction

The Little Man Computer (LMC) is an instructional model of a computer, created by Dr. Stuart Madnick in 1965. The LMC models a simple von Neumann architecture computer—which has all of the basic features of a modern computer.

This project was made for the CSCI 2122 Computer Systems class in my degree.

The lpc has a 100-word memory. The memory locations are referred to by their memory address, which are 2-digit location numbers: 00, 01 ...... 99. The first instruction of any lpc program must be at location 00. Each instruction is a 4-digit word. The sign of a lpc instruction is always positive while a data word can be positive or negative. Each location in the lpc memory contains an instruction or a data value or is unused. The first two digits of a lpc instruction are its op-code, which specifies the operation to be performed. The op-codes are given below. The last two digits of an instruction word are the operand, which is the memory location of the word to which the instruction applies.

Features

• Instruction Set Architecture (ISA): LPC uses a minimalistic set of instructions to perform operations like reading input, writing output, arithmetic calculations, and control flow.

• Memory Management: It simulates a simple memory model where each memory location can store a three-digit integer, facilitating the understanding of how data is stored and manipulated.

• Example Programs: The repository includes example LPC programs that demonstrate various functionalities, such as comparing numbers, summing values, and finding the largest number in a series.

Getting Started

To get started with the Little Person Computer:

1. Clone the Repository:

git clone https://github.com/roshankapur/littlePersonComputer.git

2. Build the Project: Navigate to the project directory and compile the source code using the provided Makefile:

cd littlePersonComputer
make

3. Run the LPC Simulator: After building the project, you can run the LPC simulator:

./lpc

LPC Instruction Set

This table summarizes the instruction set for the Little Person Computer, detailing the opcode, instruction, and a brief description of each operation.

Opcode	Instruction	Description
1XX	INP	Read input and store in memory
2XX	OUT	Output value from memory
3XX	ADD	Add value from memory to accumulator
4XX	SUB	Subtract value from memory
5XX	STA	Store accumulator in memory
6XX	LDA	Load value from memory to accumulator
7XX	BRA	Branch to address
8XX	BRZ	Branch if accumulator is zero
9XX	BRP	Branch if accumulator is positive
000	HLT	Halt the program

Note: 'XX' represents the memory address (00-99).

Example Programs

Here are some example LPC programs included in the repository:

1. Compare Two Numbers: Reads two numbers and prints the larger value.

1009  // INP: Read first number into address 09
2009  // LDA: Load value from address 09
300A  // ADD: Add value from address 0A
210B  // STA: Store result in address 0B
110B  // OUT: Output value from address 0B
0000  // HLT: Halt program

2. Add Two Numbers: Reads two numbers, adds them, stores the result, and prints it.

1009  // INP: Read first number into address 09
2009  // LDA: Load value from address 09
300A  // ADD: Add value from address 0A
210B  // STA: Store result in address 0B
110B  // OUT: Output value from address 0B
0000  // HLT: Halt program

3. Sum N Positive Numbers: Sums a series of positive numbers entered by the user until a negative number is entered, then outputs the sum.

1009  // INP: Read number into address 09
2009  // LDA: Load value from address 09
310A  // SUB: Subtract value from address 0A
800E  // BRZ: Branch to address 0E if zero
7000  // BRA: Branch to address 00
110A  // OUT: Output value from address 0A
0000  // HLT: Halt program

4. Find the Largest Number: Reads a series of numbers and outputs the largest one.

1009  // INP: Read number into address 09
2009  // LDA: Load value from address 09
310A  // SUB: Subtract value from address 0A
800E  // BRZ: Branch to address 0E if zero
7000  // BRA: Branch to address 00
110A  // OUT: Output value from address 0A
0000  // HLT: Halt program

5. Compute Average of Numbers: Reads a specified count of numbers and computes their average.

1009  // INP: Read number into address 09
2009  // LDA: Load value from address 09
310A  // SUB: Subtract value from address 0A
800E  // BRZ: Branch to address 0E if zero
7000  // BRA: Branch to address 00
110A  // OUT: Output value from address 0A
0000  // HLT: Halt program

What's Next?

I want to host a page on Vercel that has an interactive terminal window that is running this code in the background - maybe i will rewrite the ISA in JS to make the hosting easier.