Welcome to your deep dive. We're going to be looking at Raspberry Pie assembly language programming, specifically excerpts from the book Raspberry Pie Assembly Language Programming by Steven Smith. It's a twenty nineteen book, awesome, And you know you want to learn how to program your Raspberry Pie using assembly, right, and we're going to help you get the most out of this book.
Yeah, this deep dive is your shortcut to understanding all the core concepts of assembly, Okay, and it'll give you the knowledge to write more efficient code nice potentially even create your own operating systems or programming languages.
Okay, so let's get into it. Yeah, why even learn assembly in a world full of Python and JavaScript and C plus plus and all these high level languages. Don't they make assembly kind of Yeah, that's.
A great question. Obsolete, it is, and the book actually addresses that right away.
Okay.
You know, while high level languages are great for lots of tasks, assembly is still relevant for a bunch of different reasons. So think about it this way. High level languages let you drive a car without even knowing how the engine works. Right. Assembly is like being a mechanic. You can tinker with the engine directly.
Okay, so more control and power, but also more complexity exactly.
So learning assembly gives you that deeper understanding of how the Raspberry Pies processor works. It's built on the ARM architecture, okay, and this knowledge is really useful for like writing highly optimized code, understanding computer architecture at a fundamental level, creating low level software like operating systems, or even like reverse engineering or security analysis.
Yeah, creating an operating system with assembly sounds intense, but I guess that's that level of control we're talking about.
Yeah, that's right.
So to unlock the secrets of assembly, we need to understand this ARM architecture first.
Right, absolutely, The airm architecture is like a blueprint for your Raspberry Pies processor, okay. And one of the key concepts here is that airm uses a load store architecture that before any data can be processed, it has to first be loaded from memory into registers. These registers are like the processors workbenches, interesting, so the data needs to be on the workbench before the processor can work with it.
So there's this constant movement of data between memory and registers. That's right, isn't that inefficient.
You might think so, but it's actually a very efficient system.
Okay.
The book also explains how the thirty two bit ARM architecture handles fitting both addresses and data, which are also thirty two bits long, into instructions okay, and then, of course, the program counter acts as a guide, always pointing to the next instruction and memory.
Okay, I'm starting to get the picture, but you know me, I always learn best by seeing code and action. The book starts with the classic Hello World example, Right, yeah, what can we learn from that?
The Hello World example is a great starting point.
Okay.
Even in this simple program we see fundamental concepts like the dot data section for storing data, the MOV instruction for moving data into registers, and the LDR instruction for loading data from memory.
Okay, so, even with Hello World, we're already talking directly to the hardware.
Got it?
What else makes the assembly version of this program special?
This example also introduces us to the idea of system calls.
Okay.
So to print Hello World to the console, the program has to interact with the Linux operating system. It does this through a system call using the SDC instruction. Okay, and there's even a tool called obdump that lets us disassemble the program, revealing the underlying binary code that the processor actually executes.
Whoa, Okay, that's getting down to the nitty gritty right Before we move on, though, can we talk about numbers for a second. Sure, binary math has always intimated me a little bit. How does assembly handle that?
You're not alone?
Okay? Good.
The book explains how computers use the system called two's compliment to represent negative numbers. It might seem strange at first, but it actually simplifies arithmetic operations for the processor.
Okay.
We also touch on the concept of indianness Danus. It's the way multibyte data is ordered in memory, which varies between computer architectures. The Raspberry Pi uses little endian format.
Okay. So we've got this whole system for handling negative numbers and figuring out how data is arranged, right, What about actually doing calculations with assembly?
So the book dives into instructions like mv and MVN for moving data and calculating one's compliment okay, which is related to two's complement.
Okay.
Then there are eightyds instructions for addition, where adds even takes into account a potential carryover from the previous operation. You also learn how to use shifting and rotating bits to efficiently multiply or divide numbers by powers of two.
This is all fascinating, but I can imagine writing all this code by hand could get pretty tedious.
Yeah, for sure.
Are there any tools that can help us out?
You bet?
Okay.
The book introduces the g and U Assembler okay, or AS, which transforms your human readable assembly code into the machine code that the Raspberry Pie understands. Right. Then there's the g and U Debugger or GDB okay, a powerful tool that lets you step through your code, examine variables, and hunt down bugs.
So AS is like a translator in GDB is like a detective for your code.
It's exactly.
That sounds way better than counting bits by hand, Yeah, it is.
What about managing larger projects with lots of code?
For that, there's the Make utility okay. It's like a project manager for your code. Interesting, automating the build process and making sure everything's organized. Okay. The book even provides examples of make files, which are like recipes for building your assembly programs.
This is all starting to make sense, You got the tools and the instructions right. But so far we've only talked about simple programs. How do we create more complex logic in assembly? How do we make decisions and create programs that can do different things based on certain conditions.
So that's where program flow control comes in, and that's what we'll be diving into in the next part of our deep dive.
All right, let's do it. Welcome back to our deep dive into Raspberry Pie assembly language programming. Last time, we explored, you know, the fundamentals of ARM architecture and some basic assembly instructions. We even learned about tools that make assembly programming easier, and we ended on the topic of program flow control, which is how we add decision making and more complex logic to our programs.
Exactly, I'm really eager to learn how to make our assembly programs, you know, smarter and more responsive to different situations.
Well, the key to understanding program flow control lies in a special register called the current program Status Register or CPSR.
CPSR like a dashboard.
For your code, displaying important status flags that reflect the outcome of the last instruction executed.
A dashboard, so it tells us what's happening inside.
The program precisely, The CPSR contains flags like the zero flag or Z, which is set if the result of an operation is zero, the negative flag or N if there was a negative gotcha, the carry flag or see if an addition results in a carry, and the overflow flag or V if an arithmetic operation overflows.
So these flags are like signals that indicate the current state of the program exactly.
And this is where it gets interesting. Okay, we use the CMP instruction to compare values based on the comparison these flags in the cps are are set. Then we can use conditional branch instructions like b eq, bn, BLT and others to change the flow of execution based on those flags.
So cmp sets the stage and then the branch instructions decide which path the code should take. It's like having to choose your own adventure story for our program.
That's a great analogy. Awesome, And as your programs become more complex, it's important to write structured, organized code to avoid like a tangled mess of branches.
Right.
This is where the concept of structured programming comes in, minimizing unnecessary jumps and keeping your code clean.
Okay, structured programming for the win. Yeah, but what about when we want to break down our programs into smaller, reusable chunks. Can we do that in assembly?
Absolutely, that's where functions come in. Functions are like many programs within your main program, allowing you to group instructions, reuse logic, and make your code more modular.
So it's like building with legos. We can create these reusable modules that we can just put together to make bigger programs exactly.
And to manage the flow of execution between functions, we use this structure called the stack.
Okay, the stack.
The stack is a dedicated area of memory that operates like a pile of plates.
Okay.
Use push to place data onto the stack and pop to take it off.
So it's a last in, first out LIFO system.
Precisely, this is crucial for function calls. Okay. When a function is called, it's parameters, local variables, and the address to return to. After the function finishes, we call that the return address are pushed onto the stack. The BL instruction that stands for a branch with link handles this function call process.
So when the function is done and it just pops everything back off the stack and returns to where it left off exactly.
The stack is like a temporary workspace for functions. The book even goes into detail about the concept of stack frames, which are like individual compartments on the stack for each function call, keeping everything organized and preventing data from getting mixed up.
That's pretty clever. It's amazing how assembly can be so structured, even though it's such a low level language. It is, but so far we've been mostly focused on the internal workings of our programs. Can we use assembly to interact with the outside world.
Absolutely, But the next part of the book dives into how to communicate with the Linux operating system from our assembly code, which opens up a world of possibilities.
Welcome back to our deep dive into Raspberry Pie assembly language programming. We've talked about a lot, you know, ARM architecture, program flow control, functions, the stack. Right last time, you mentioned interacting with the Linux operating system from assembly. Yeah, that sounds like a big step it is.
The ability to tap into the operating systems capabilities really opens up a whole new level of functionality for your assembly programs. Okay, the book explains how we can make use of Linux system calls directly from our assembly code.
So what kind of things can we actually do with these system calls?
Lots of things.
Okay.
System calls are like requests we make to the operating system.
Okay.
We can read and write files, mannix processes, work with the network, even control hardware connected with the Raspberry Pie.
Controlling hardware with assembly sounds pretty powerful, it is. Can you give me an example.
Sure. One chapter of the book focuses specifically on programming the Raspberry pies gpio pins. GPIO that sounds for general purpose input output.
Okay.
This lets you interface with external devices like LEDs, sensors, motors, and more.
So we could write assembly code to make an LED blink.
You got it.
That's pretty cool. How do we actually control these gpio pins from assembly though?
The book describes two methods. The first involves interacting with the Linux GPI io device driver by reading and writing special files in the cisclass GPO directory.
Okay.
The second method involves directly accessing the gpio controllers registers using memory mapped IO.
Memory mapped IO what is that?
It's a technique where specific memory addresses are mapped to physical hardware registers.
Okay?
By writing to these memory addresses, we can directly control the hardware.
Okay.
The book explains this concept in detail, including the role of virtual memory and how it allows us to access physical memory.
It's amazing how we can get so close to the hardware with assembly. It is so we can control the operating system. We can even control hardware. Is there anything assembly can't do well?
Assembly is fantastic for low level tasks where speed and efficiency are crucial, okay, But for more complex applications, higher level languages like C or Python are often more practical.
Okay.
However, the book shows us that assembly doesn't have to live in isolation. It can work alongside these higher level languages.
So we can combine the power of assembly with the flexibility of languages like C and Python.
Exactly. The book explains how to cool C functions from assembly, and how to create assembly libraries that can be used by C programs. Wow. You can even embed assembly code directly within C code using gccs ASM statement, And for Python you can use the c types module to call assembly functions.
That opens up a lot of possibilities.
It does, Okay.
Before we wrap up, you mentioned earlier that the book covers advanced arithmetic operations multiplication and division. Can you tell me a little bit more about that?
Sure? Multiplication and ERM assembly can involve instructions like mool, which gives you the lower thirty two bits of the results, or instructions like symbol and umll, which calculate the full sixty four bit product. Division is handled by instructions like sdiv and UDIV on modern ARM and processors. Okay, but earlier versions didn't have dedicated division instructions.
So they had to come up with clever workarounds exactly.
The book delves into the history of division algorithms on ARM, which is fascinating interesting. It also covers multiply accumulating instructions like MLA and smlal, which combine multiplication and addition into a single operation, making them incredibly efficient for certain calculations.
Yeah, that sounds like it would be really useful for tasks like image processing or machine learning.
Absolutely.
Yeah.
And speaking of powerful features, the book also introduces us to the neon coprocessor neon, a specialized unit designed for parallel processing of vectors and matrices. This coprocessor extends the capabilities of the floating point unit, providing instructions for vector arithmetic, data rearrangement, and more.
Neon sounds like it could really boost performance for certain applications.
It can awesome. And finally, the book touches on the transition from thirty two bit to sixty four bit ARM known as arch sixty four. Okay, this newer architecture brings an expanded register set, changes to the function calling conventions, and even the removed of conditional execution, relying instead on sophisticated branch prediction techniques.
Wow, we've covered so much. This deep dive has taken us from the very basics of AIRM assembly to advance features like neon and sixty four bit architecture. Right, it's incredible how much depth there is to this seemingly simple language.
Yeah, it really highlights how assembly, even in a world of high level languages, continues to be relevant. It gives you a level of control and understanding that's just not possible with higher level abstractions.
I'm definitely feeling inspired to learn more. But before we go, there's one thing I'm still a bit apprehensive about. Yeah, reading and understanding existing assembly code. It seems so dense and cryptic.
It can be challenging, but remember assembly code is built on the same fundamental concepts we've been discussing. The book provides some great strategies for tackling this challenge. Okay, the key is to approach it methodically.
Methodically how so, first.
Understand the context of the code, what's its purpose, what problem is it trying to solve. Then break the code down into smaller, more manageable chunks. Look for familiar patterns, data structures, arithmetic operations, control flow structures.
So it's like solving a puzzle piece by piece exactly.
And don't be afraid to use tools. A debugger is invaluable for stepping through code, examining values, and seeing how the instructions affect the program state. Okay, for really complex code, there are even tools like Guidra which can help decompile assembly code back into a higher level representation, making it easier to analyze.
This Deep Dog has been an incredible journey. We've explored the power and flexibility of Raspberry Pie assembly language programming, going from basic concepts to advanced techniques it has.
It's been amazing, and most importantly, we've seen that assembly is not some arcane forgotten language. It's a vital tool for understanding how computers work at the most fundamental level, yeah, giving you the ability to write highly efficient code and even push the boundaries of what's possible with hardware.
A huge thanks to Steven Smith for writing Raspberry high assembly language programming, and to you our listeners for joining us on this deep dive. Until next time, keep exploring, keep learning, and keep pushing the limits of what you can create.