#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use cortex_m_semihosting::hprintln;
use stm32f3xx_hal::prelude::*;
                    
#[entry]
fn entry() -> ! {
    extern "C" {
        static _user_stack_start: u32;
    }

    // set unprivileged stack
    unsafe {
        let stack_addr = &_user_stack_start as *const u32 as u32;
        cortex_m::register::psp::write(stack_addr)
    };
    
    let mut ctrl_reg = cortex_m::register::control::read();
    ctrl_reg.set_npriv(cortex_m::register::control::Npriv::Unprivileged);
    ctrl_reg.set_spsel(cortex_m::register::control::Spsel::Psp);

    // enter unprivileged mode
    unsafe { cortex_m::register::control::write(ctrl_reg) };

    main();
}

fn main() -> ! {
    hprintln!("hello");

    loop {}
}