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Little Man Computer

PTBR Documentation | Simulator | Commands

Objective

  • The Little Man Computer (LMC) provides a simplified model of a computer, making it an easy-to-understand teaching tool for computer science and programming students.

  • Through working with the LMC, students gain a deeper understanding of computer architecture and the basics of pipelining, which are fundamental concepts in computer science.

  • The hands-on approach to programming with the LMC provides practical experience that can be applied in real-world computer systems design and optimization.

About us

We are third-semester Computer Science students at the Pontifical Catholic University of Paraná (PUCPR). This project was a challenge proposed by Professor Frank de Alcantara in the subject Performance in Cyber-Physical Systems.

Commands and Structure

Writting for LMC

Codes for Little Man Computers are a set of simple instructions that simulate the instructions of a real computer. The LMC has an accumulator, that keeps one value for operations.

Here are some simple LMC codes that use most of its features.

This code takes one input and counts from it to 0.

	INP
loop	OUT
	STA count
	SUB one
	STA count
	BRP loop
	HLT

one     DAT 1
count	DAT

This code adds the inputed numbers

	INP
	STA	number     
	INP     
	ADD	number
	OUT
	HLT

number	DAT

Labels

Labels can be used to increase the complexity of the code, to apply conditions or loops. To create a label, type any name followed by ":" and the first command that should be excecuted when jumped to the label.

Creating labels

#Label named "label1"
label1    OUT
          HLT

#Label named "label2"
label2    HLT

#Label named "anyname"
anyname   INP
          HLT

To branch to a certain label use jump commands.

All Commands

Input

Command: INP

OPCODE: 901

Will take the next user input and add it to the accumulator. If there are no more inputs, the value added to the accumulator will be 0.

Usage

# User input: 1 | 2 | 3

  INP

# User input: 1 | 2
# Accumulator: 3

Output

Command: OUT

OPCODE: 902

Will add to the output list the accumulator value

Usage

# Output: 2 | 3
# Accumulator: 1

  OUT
  
# Output: 1 | 2 | 3

Add

Command: ADD [ pos ]

OPCODE: 1xx

Will add the value located at the specified position to the accumulator.

Usage

# Accumulator: 2
# Value at postion 3: 5

  ADD 3
  
# Accumulator: 7

Subtract

Command: SUB [ pos ]

OPCODE: 2xx

Will subtract the value located at the specified position to the accumulator.

Usage

# Accumulator: 7
# Value at postion 3: 5

  SUB 3
  
# Accumulator: 2

Load

Command: LDA [ pos ]

OPCODE: 5xx

Will load the value inside a RAM Slot to the accumulator.

Usage

# Value at position 3: 5

  LDA 3
  
# Accumulator: 5

Store

Command: STA [ pos ]

OPCODE: 3xx

Will store the current accumulator value inside the specified RAM position.

Usage

# Accumulator: 2

  STA 3
  
# Value at position 3: 2

Dat

Command: LDA [ pos ]

OPCODE: 5xx

Will load the value inside a RAM Slot to the accumulator.

Usage

# Value at position 3: 5

  LDA 3
  
# Accumulator: 5

Store

Command: [ name ] DAT (optional: [ value ])

OPCODE: None

Will name a RAM Slot. This command is not executed when the code is running, only before, when loading the code to the RAM. It is possible to pass a initial value. This command should be added AFTER the end of the code.

Usage

x DAT
y DAT 12

# On the first free slot after the commands: RAM slot named x, value: 000
# On the second free slot after the commands: RAM slot named y, value: 12

When using DAT, commands accept the position name

      LDA x
      STA y
      ADD z
      SUB name

x     DAT
y     DAT
z     DAT 1
name  DAT 3

Jumps

There are three types of jumps. All jumps will go to the specified label if the conditions are met.

Branch Always

Command: BRA [ Label ]

OPCODE: 6xx

Will always branch to the specified label

Usage

      BRA exit

exit  HLT

Branch if Positive

Command: BRP [ Label ]

OPCODE: 8xx

Will only branch to the specified label if the accumulator value is positive.

Usage

# Accumulator value: 1
      BRP exit

exit  HLT

Branch if Zero

Command: BRZ [ Label ]

OPCODE: 7xx

Will only branch to the specified label if the accumulator value is positive.

Usage

# Accumulator value: 0
      BRZ exit

exit  HLT

Halt

Command: HLT

OPCODE: 000

Will halt the execution of the code.