To  get started without any tool hiccups we will be using online tool. Open :  https://cpulator.01xz.net/?sys=arm

Let's go through the provided minimal ARM assembly program line by line:

```assembly
.global _start   // Declare the start of the program and make _start visible to the linker
```
- This line is a directive indicating that `_start` is a global symbol and should be visible to the linker. The linker uses this information to know where the program execution should begin.

```assembly
.section .text   // Start of the code segment
_start:          // Program entry point
```
- The `.text` directive indicates the beginning of the code segment, where the actual instructions of the program are placed.
- `_start` is a label representing the entry point of the program. The program execution begins here.

```assembly
    // Halt the program
    mov r7, #1    // Move the value 1 into register r7
    swi 0         // Trigger a software interrupt to terminate the program
```
- `mov r7, #1`: This instruction moves the immediate value 1 into register `r7`. In this case, it is preparing the value that will be used to specify the type of action in the software interrupt.
 
- `swi 0`: This instruction triggers a software interrupt (SWI) with a software interrupt number of 0. SWI 0 is commonly used as a convention to request an operating system service or to terminate a program gracefully. In this minimal program, it serves as a way to halt the execution.

​

A bit about types of Registers in ARM Architecture:

ARM architecture has several types of registers, categorized based on their usage:

1. **General-Purpose Registers (R0-R15):**
   - R0 to R12: General-purpose registers used for various purposes.
   - R13 (SP): Stack Pointer, used to manage the program stack.
   - R14 (LR): Link Register, used to store the return address when calling subroutines.
   - R15 (PC): Program Counter, holds the address of the next instruction to be executed.

2. **Status Registers:**
   - CPSR (Current Program Status Register): Contains flags and other status information.

3. **Banked Registers:**
   - Some registers have banked versions that are used in different processor modes (e.g., IRQ, Supervisor, etc.).

4. **Floating-Point Registers:**
   - F0 to F31: Floating-point registers used for floating-point operations.

5. **Vector Registers:**
   - Q0 to Q31: Quadword registers for Advanced SIMD (NEON) operations.

In the provided minimal program, we use a general-purpose register (`r7`) to hold the value 1, and the program utilizes the Program Counter (`r15`) implicitly as it executes the SWI instruction. The specifics can vary based on the ARM architecture version and the context of the program.

​

​

Simple tasks: 

Can you modify the program to update all the register values? 
Also play around by executing each instruction one after another and note the changes in PC values.