Rust demo for Pi 3 bare metal

rpi3_rust_led.rs

#![feature(asm)]
#![feature(lang_items)]
#![crate_type = "staticlib"]
#![no_std]

const GPIO_BASE: u32 = 0x3F200000; // base address for Pi 2 and Pi 3

fn sleep(value: u32){
    for _ in 1..value {
        unsafe { asm!("");}
    }
}

#[no_mangle]
pub extern fn main() {
    let gpio = GPIO_BASE as *const u32;
    // Set SEL0 reg, 15-17 bits to 1 to use Pin 15 (1 Pin = 3 bits)
    let sel = unsafe { gpio.offset(0) as *mut u32 };
    // Set SET0 reg, 5th bit to 1
    let on = unsafe { gpio.offset(7) as *mut u32 };
    // Set CLR0 reg, 5th bit to 1
    let off = unsafe { gpio.offset(10) as *mut u32 };
    unsafe {
        // use Pin 15
        *sel |= 1 << 15;
    }
    loop {
        unsafe {
            *off = 1 << 5;
        }
        sleep(500000);
        unsafe {
            *on = 1 << 5;
        }
        sleep(500000);
    }
}

#[lang = "eh_personality"]
extern fn eh_personality() {}

#[lang = "panic_fmt"]
extern fn panic_fmt() {}

#[no_mangle]
pub extern fn __aeabi_unwind_cpp_pr0() {}
// rustc --target arm-unknown-linux-gnueabihf -O --emit=obj src/kernel.rs
// arm-none-eabi-gcc -O3 -mcpu=cortex-a53 -mfpu=neon-fp-armv8 -mfloat-abi=hard -funsafe-math-optimizations -nostartfiles kernel.o -o kernel.elf
// arm-none-eabi-objcopy kernel.elf -O binary kernel.img
// copy kernel.img, start.elf, bootcode.bin to SD card
// connect pin 5 to led
// power on the pi