My Journey into Learning 6502 Assembly and Beyond

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Learning 6502 assembly language has been both hard and fun. I love old computers, and this has helped me understand how they work better. Here's what I've learned and done, from 6502 assembly to modern 64-bit assembly languages like AArch64 and x86_64.

Discovering the 6502 Microprocessor

The 6502 microprocessor was used in famous old devices like the Apple II and the NES. It's simple and a great way to learn low-level programming. I started with flow control and math operations.

Flow Control in 6502 Assembly

Flow control is about controlling where the program goes. The main tools are:

  • JMP (Jump): Go to a new place in the program.
  • Branches (Bxx): Go to a new place if a condition is met.
  • Subroutines (JSR and RTS): Call and return from a function.

These tools help make loops, decisions, and reusable code. Writing a loop or a function was like putting together a puzzle.

Mastering Math Operations

The 6502 can do basic math directly:

  • ADC (Add with Carry): Add numbers.
  • SBC (Subtract with Borrow): Subtract numbers.
  • INC/DEC (Increment/Decrement): Add or subtract one.

Using these, I could do more complex math, like working with larger numbers.

Working with Strings

Strings in 6502 assembly are sequences of bytes, each representing a character. Working with strings involves carefully moving through these bytes.

  • String Length Calculation: Finding the end of a string.
  • String Copy: Moving characters from one place to another.
  • String Comparison: Checking if two strings are the same.

These tasks are the basics for handling text.

Lab Exercises: Applying Knowledge

Lab exercises helped me apply what I learned:

  • Multi-byte Addition Function: Adding large numbers.
  • String Concatenation Routine: Joining two strings.
  • Basic Text Editor: Simple text features within memory limits.

These exercises made the concepts clearer.

Exploring Modern 64-bit Assembly

Learning modern 64-bit assembly languages like AArch64 and x86_64 was a big step. The new architectures and instructions were challenging but interesting.

Essential Resources

I used many resources to help me:

  • Assembly Language Basics: Foundational knowledge.
  • GNU Assembler (GAS): Instructions on using this assembler.
  • System Calls (Syscalls): For interfacing with the OS.
  • Quick-Start Guides for 64-bit Architectures: Including reference manuals.
  • Register and Instruction Quick Start Guides: Handy references for these architectures.

Reflecting on the Journey

Learning 6502 and modern assembly languages has been enriching. These skills apply to both old and new systems.

Conclusion

Learning 6502 assembly has helped me understand the basics of computing and prepared me for more advanced programming. From flow control and math to strings and modern architectures, each step has been valuable.

Whether you're interested in old computers or modern programming, I encourage you to try this journey. The challenges are great, but the rewards are even greater, offering a deep appreciation for assembly language. 

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