How to Program ARM Assembly Language for Beginners

TL;DR

ARM assembly is a low-level language closest to machine language, found in over 200 billion devices including phones and new MacBooks. Registers store 32 bits (a word) of data close to the CPU for fast access, while slower stack memory in RAM holds larger, more complex data sets. Learning ARM teaches assembly principles that transfer to x86 and other architectures.

Transcript

assembly language is a low level programming  language for a computer or other programmable device that is closest to the machine language.  It is often specific to a particular computer architecture. So there are multiple types  of assembly languages arm is an increasingly popular assembly language, Scott Cosentino teaches  this course about assem... Read More

Key Insights

• ARM is a low-level assembly language specific to a particular computer architecture, and it is closest to machine language. Over 200 billion devices contain an ARM chip, making the language valuable to understand for anyone working close to hardware.
• Working at a lower level lets programmers be closer to the hardware, enabling better and more efficient interactions between hardware and software in situations that require direct hardware control.
• ARM chips power many embedded devices, Android and some iPhone devices, and newer laptops like the new MacBooks, which now use ARM-based processors instead of older architectures.
• Registers are memory areas very close to the CPU, so they can be read and written quickly, but they hold a limited amount of data. This course uses an ARMv7 D1 SoC, a 32-bit processor.
• A word is the maximum data size that fits in a register: 32 bits on a 32-bit processor, 64 bits on a 64-bit processor. A half word is half that size, a byte is always eight bits.
• Registers R0 through R6 are general purpose, while R7 has a special function for system calls. Storing a numerical value in R7 tells the operating system which action to perform when the program interrupts.
• Stack memory is stored in the computer's RAM, making it slower to access and write than registers, but it can store far more data and is used to represent complex sets like a list of numbers.
• The stack pointer (SP) register always holds the address of the next available piece of memory on the stack. Addresses increase by four each step, and all values are represented in hexadecimal.

Questions & Answers

Q: What is ARM assembly language and why is it worth learning?

ARM assembly is a low-level programming language for a computer or programmable device that is closest to the machine language, and it is often specific to a particular computer architecture. It is an increasingly popular assembly language, and it is estimated that over 200 billion devices contain an ARM chip. Understanding it lets programmers work at a lower level, allowing them to write code that interacts with hardware in an efficient manner.

Q: What devices use ARM-based processors?

ARM processors appear in a wide variety of applications, especially embedded devices. Popular consumer devices such as phones use them, including a lot of Android devices and some iPhone devices running ARM-based chips. ARM is also becoming much more widely used in laptops, with the new MacBooks now using ARM-based processors. This growing adoption makes understanding how ARM processors work and how to program directly with them an important skill.

Q: What emulator does this course use and do you need special hardware?

The course primarily uses a free online emulator called CPUlator, which runs in a web browser so you can access it from almost any computer without installing special equipment. It demonstrates the ARMv7 D1 SoC architecture. You can follow along entirely in the emulator, though the final Linux-based videos require a Linux machine or virtual device. The approach avoids special prerequisites so learners can participate easily.

Q: What is a register in ARM assembly?

A register is an area in memory that is very close to the CPU, so it can be accessed and written to quickly, giving relatively fast storage. However, registers hold a limited amount of data. In the 32-bit processor used in this course, each register displays eight hexadecimal values, and since each hex value represents four bits, a single register stores a total of 32 bits of data.

Q: What does the term 'word' mean in assembly?

A word refers to the maximum size of data that can be stored in a register. In a 32-bit processor a word is 32 bits, while in a 64-bit processor a word would be 64 bits. A half word is half that size, so 16 bits in a 32-bit system and 32 bits in a 64-bit system. A byte is always eight bits, and below that is a single bit of data.

Q: How are ARM registers used and what makes R7 special?

Registers R0 through R6 are general purpose, so they can be used for whatever storage you like. R7 has a special function related to system calls. When assembly code needs to talk to the operating system to request a resource or terminate a program, it stores a numerical value in R7 that maps in a table to a specific action. For example, storing the value one in R7 and then interrupting the program tells the operating system to exit the program.

Q: What is stack memory and how does it differ from registers?

Stack memory is typically stored in the computer's RAM. It is slower to access and slower to write to than registers, but it can store much more data. Stack memory is typically used when representing more complex sets of data, such as a list of numbers, where each memory location holds a specific number that you can iterate through. Registers, by contrast, are fast but limited to a single word of data.

Q: How does the stack pointer and memory addressing work?

The SP register is the stack pointer, and it always points to the address of the next available piece of memory on the stack. Memory addresses on the stack increase by four each step, so consecutive locations sit at address zero, four, eight, twelve, sixteen, and so on. All these values are represented in hexadecimal, so a displayed '10' actually means 16 in decimal. Keeping the hexadecimal representation in mind is important when reading memory locations.

Summary & Key Takeaways

• Scott Cosentino teaches an introduction to ARM assembly, a low-level language closest to machine language and specific to a computer architecture. With over 200 billion devices containing ARM chips, including phones and new MacBooks, understanding ARM lets programmers work closer to hardware and write more efficient hardware-software interactions.

• The course uses the free online CPUlator emulator running an ARMv7 D1 SoC, so learners can follow along in a browser without special equipment. It covers basic instructions, arithmetic, logical and shift operators, branching, loops, and hardware interactions, with the final Linux-based videos requiring a Linux machine or virtual device.

• Registers sit close to the CPU for fast storage but hold only 32 bits, called a word. R0 to R6 are general purpose while R7 handles system calls. Stack memory in RAM is slower but larger, holding complex data; the SP register tracks the next available stack address, incrementing by four in hexadecimal.