Lecture Notes: LC3 and MIPS Assembly

Introduction

• Focus on LC3 and MIPS assembly.
• Discuss differences in instructions and similarities.
• Cover programming constructs, debugging principles, conditional statements, loops, arrays, and function calls.
• Context: One model Oney machine and instruction cycle.

Building LC3 Programs

• Example: Simple program with 12 integers stored from addresses hex 3100 to hex 31OB.
• Problem-solving approach: Translate problem to an algorithm using flowcharts.
• Setup:
  • Address of first integer in 3100.
  • Counter in R3, number of integers in R2.
• Process:
  • Initialize registers.
  • Check if R2 (number of integers left) is zero.
  • If not, load integer, add, increment address, decrement counter.
  • Loop until done; output result.

LC3 Assembly Instructions

• Use of conditional branches to create loops.
• Instructions like load effective address for managing addresses.
• Importance of correctly managing branch targets.

Debugging LC3 Programs

• Debugging focuses on tracing program execution and verifying results.
• Useful technique: Partition program into parts/modules.
• Interactive debugging operations:
  • Put values into memory and registers.
  • Execute instruction sequences.
  • Set breakpoints to stop execution.

Programming Constructs in MIPS

• Importance of divide and conquer in programming.
• Three basic constructs:
  • Sequential: Execute tasks in sequence.
  • Conditional: Use if/else constructs to execute subtasks based on conditions.
  • Iterative: Use loops to repeat tasks based on conditions.

MIPS Programming

• Conditional constructs with conditional branches.
• Usage of Branch if Equal.
• Implementation of loops using conditional and unconditional branches.
  • Example: While loop to calculate power of two.
  • Example: For loop to add integers.

Arrays in MIPS

• Accessing arrays involves loading base address into a register.
• Load upper immediate and or immediate for loading addresses.

Function Calls and Conventions

• Need for functions to enhance code reuse and readability.
• Function call conventions:
  • Arguments in registers a0 to a3.
  • Return value in v0.
  • Jump and Link (jal) for calling functions.
  • Jump Register (jr) for returning from functions.

Stack Usage for Function Calls

• Stack: To save local variables and registers during function calls.
• Stack Pointer: Points to top of the stack.
  • Usage: Save registers before function call and restore after.
  • Conventions:
    • Temporary registers can be overwritten.
    • Preserved registers (s0, s1, ...) must be saved and restored.

Conclusion

• Overview of LC3 and MIPS assembly programming.
• Emphasized debugging, conditional branches, loops, arrays, and function call conventions.
• Key takeaway: Understanding and following conventions is crucial for effective assembly programming.