Pros of linux

• Full-featured, production-ready Linux kernel for Raspberry Pi
• Extensive hardware support and drivers for various Raspberry Pi models
• Regular updates and maintenance from the official Raspberry Pi team

Cons of linux

• Large codebase, potentially overwhelming for beginners
• Steeper learning curve for those new to kernel development
• Less focused on educational purposes compared to raspberry-pi-os

Code Comparison

raspberry-pi-os:

void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
{
    uart_init();
    uart_send_string("Hello, world!\r\n");

    while (1) {
        uart_send(uart_recv());
    }
}

linux:

asmlinkage __visible void __init start_kernel(void)
{
    char *command_line;
    char *after_dashes;

    set_task_stack_end_magic(&init_task);
    smp_setup_processor_id();
    debug_objects_early_init();
    // ... (more initialization code)
}

The raspberry-pi-os example shows a simple kernel entry point, while the linux code demonstrates a more complex initialization process typical of a full-featured kernel.

Pros of Circle

• More comprehensive and feature-rich, offering a complete bare metal environment
• Better documentation and examples for various Raspberry Pi models
• Active development with regular updates and bug fixes

Cons of Circle

• Steeper learning curve due to its complexity
• Less focused on educational purposes compared to raspberry-pi-os
• May be overwhelming for beginners or those seeking a minimalistic approach

Code Comparison

raspberry-pi-os:

void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
{
    uart_init();
    uart_send_string("Hello, world!\r\n");

    while (1) {
        uart_send(uart_recv());
    }
}

Circle:

#include <circle/startup.h>

class CKernel
{
public:
    CKernel(void) {}
    bool Initialize(void);
    TShutdownMode Run(void);
};

CKernel kernel;
CKernel *pKernel = &kernel;

The raspberry-pi-os example shows a simple bare-metal kernel with UART communication, while Circle demonstrates a more structured C++ approach with initialization and run methods. Circle's code reflects its more comprehensive nature, offering a fuller development environment for Raspberry Pi projects.

Pros of raspi3-tutorial

• More comprehensive coverage of low-level hardware interactions
• Includes graphics programming and USB support
• Provides a broader range of topics, including bootloader development

Cons of raspi3-tutorial

• Less focus on operating system concepts and design
• May be more challenging for beginners due to its low-level nature
• Fewer explanations of theoretical concepts compared to raspberry-pi-os

Code Comparison

raspberry-pi-os (scheduler implementation):

void scheduler_init(void) {
    preempt_disable();
    for (int i = 0; i < NR_TASKS; i++) {
        task[i] = NULL;
    }
    preempt_enable();
}

raspi3-tutorial (GPIO initialization):

void gpio_init() {
    *GPFSEL1 = 0;
    *GPSET0 = (1<<16);
    *GPCLR0 = (1<<16);
}

The raspberry-pi-os example focuses on task management and scheduling, while the raspi3-tutorial example demonstrates low-level hardware interaction with GPIO pins.

Pros of raspberrypi

• More comprehensive coverage of Raspberry Pi models and peripherals
• Includes examples for various programming languages (C, Python, Assembly)
• Provides detailed hardware-specific documentation and register descriptions

Cons of raspberrypi

• Less structured learning path for beginners
• Fewer explanations and tutorials on operating system concepts
• Documentation may be more technical and harder to follow for newcomers

Code Comparison

raspberry-pi-os:

void enable_interrupt_controller()
{
    put32(ENABLE_IRQS_1, SYSTEM_TIMER_IRQ_1);
}

raspberrypi:

void enable_irq()
{
    unsigned int ra;
    ra = get32(ARM_IC_BASE + ARM_IC_IRQENABLE1);
    ra |= 1 << 1;
    put32(ARM_IC_BASE + ARM_IC_IRQENABLE1, ra);
}

Both repositories provide examples for enabling interrupts, but raspberrypi uses more hardware-specific register names and bitwise operations, while raspberry-pi-os uses more abstracted function calls and constants.

raspberry-pi-os focuses on building an educational operating system from scratch, providing step-by-step tutorials and explanations of OS concepts. raspberrypi, on the other hand, offers a broader range of examples and documentation for various Raspberry Pi programming tasks, including bare-metal programming and interfacing with different peripherals.

Pros of mini-arm-os

• Simpler and more lightweight, focusing on bare-metal ARM programming
• Includes examples for both ARM7 and Cortex-M3 architectures
• Provides a step-by-step tutorial for building a minimal OS

Cons of mini-arm-os

• Less comprehensive than raspberry-pi-os in terms of OS features
• Lacks specific Raspberry Pi hardware support
• Limited to basic OS concepts without advanced functionality

Code Comparison

mini-arm-os (context switching):

void activate(tcb_t *new)
{
    current_task = new;
    context_switch(&(new->sp));
}

raspberry-pi-os (context switching):

void switch_to(struct task_struct * next) 
{
    if (current == next) 
        return;
    struct task_struct * prev = current;
    current = next;
    cpu_switch_to(prev, next);
}

Both projects demonstrate context switching, but raspberry-pi-os includes additional checks and uses a more complex structure for task management.