Introduction to ARM Assembly Language Programming
Overview
- Assembly language is a low-level programming language closest to machine language, specific to computer architecture.
- ARM (Advanced RISC Machine) assembly language is popular due to its efficiency and wide usage in over 200 billion devices.
- Scott Cosentino, a technical instructor, teaches this course on ARM assembly programming, aiming to provide a fundamental understanding of the ARM processor and assembly programming.
Course Goals
- Introduction to low-level programming concepts through ARM assembly language.
- Understanding ARM processor architecture and how to interact with hardware efficiently using ARM assembly instructions.
- Practical programming exercises using the CPULater emulator and Linux-based systems for hands-on experience.
- Encouragement to share learned concepts with peers to enhance collaborative learning.
The CPUlater Emulator
- Free online emulator used to follow along without needing special hardware.
- Works with various architectures, including ARM v7 and other assembly languages like MIPS.
- Emulating on ARM v7 D1 SOC, following similar steps to run code on actual ARM processors.
ARM Assembly Language Basics
- Registers: Special memory locations close to the CPU for fast access and storage (R0-R7 for general purpose, R7 for system calls).
- Special Registers: SP (Stack Pointer), LR (Link Register), PC (Program Counter), CPSR (Current Program Status Register).
- Memory Layout: Understanding stack memory, common sizes (word, half-word, byte), and their practical uses in code.
Basic Instructions
- Move (MOV): Moving data into registers and understanding syntax for immediate values and hexadecimal representation.
- System Calls: Using system call numbers to interact with the operating system, e.g., terminating programs.
- Arithmetic Operations: Add, subtract, multiply; handling larger numbers and setting condition flags (CPSR).
- Logical Operators: AND, OR, Exclusive OR, negation (MVN for negation).
Advanced Instructions
- Addressing Modes: Immediate, Register Direct, Register Indirect, Register Indirect with Offset, Pre and Post Increment.
- Logical Shifts and Rotates: Left and Right shifts, rotations for manipulating bits and efficient computation.
- Conditional Instructions: Conditional execution of instructions based on previous comparison results (like if-else in high-level languages).
Branching and Looping
- Branches: Implementing conditional branches to create decision-making constructs, different types (branch if equal, not equal, etc.).
- Loops: Implementing looping through branching, iterating through lists, handling list end conditions, and potential issues with uninitialized memory.
Functions and Subroutines
- Function Calls: Creating branches with links to subroutines, using LR to return to the main program after function execution.
- Preservation of Registers: Using push and pop to save and restore register values during function calls to avoid overwriting important values.
- Function Flow: Detailed handling of function execution flow, return values, and managing stack memory efficiently.
Hardware Interaction
- Emulating Devices: Using the D1 SOC emulator to interact with hardware devices like switches and LEDs.
- Input and Output: Using memory-mapped I/O to read switch states and control LEDs, practical examples of writing and reading from hardware.
Operating System Level Programming
- Emulating Raspbian: Setting up a Raspberry Pi environment using QEMU emulation to run ARM assembly on a Linux-based system.
- System Calls on Linux: Using system calls through ARM assembly for tasks like printing to standard output, facilitated by the operating system (e.g.,
write
system call).
Debugging and Memory Examination
- GDB Debugger: Using GDB to debug assembly programs on Linux, setting breakpoints, examining register and memory states, stepping through code for detailed inspection.
- Memory Inspection: Using GDB commands to examine memory contents in different formats (hexadecimal, decimal, character), understanding the memory layout of strings and other data.
Summary
This course provides a comprehensive introduction to ARM assembly language programming, covering essential concepts from basic instructions to complex function calls and hardware interactions, with practical tutorials using emulators and Linux environments.