54 lines
1.3 KiB
Rust
54 lines
1.3 KiB
Rust
|
#![no_std]
|
||
|
|
#![no_main]
|
||
|
|
#![feature(naked_functions)]
|
||
|
|
|
||
|
|
use core::panic::PanicInfo;
|
||
|
|
|
||
|
|
#[naked]
|
||
|
|
#[no_mangle]
|
||
|
|
#[link_section = ".text.init"]
|
||
|
|
unsafe extern "C" fn _start() -> ! {
|
||
|
|
use core::arch::asm;
|
||
|
|
asm!(
|
||
|
|
// before we use the `la` pseudo-instruction for the first time,
|
||
|
|
// we need to set `gp` (google linker relaxation)
|
||
|
|
".option push",
|
||
|
|
".option norelax",
|
||
|
|
"la gp, _global_pointer",
|
||
|
|
".option pop",
|
||
|
|
|
||
|
|
// set the stack pointer
|
||
|
|
"la sp, _init_stack_top",
|
||
|
|
|
||
|
|
// "tail-call" to {entry} (call without saving a return address)
|
||
|
|
"tail {entry}",
|
||
|
|
entry = sym entry, // {entry} refers to the function [entry] below
|
||
|
|
options(noreturn) // we must handle "returning" from assembly
|
||
|
|
);
|
||
|
|
}
|
||
|
|
|
||
|
|
extern "C" fn entry() -> ! {
|
||
|
|
use core::ptr::write_volatile;
|
||
|
|
let addr = 0x1000_0000 as *mut u8;
|
||
|
|
{
|
||
|
|
// Set data size to 8 bits.
|
||
|
|
unsafe { write_volatile(addr.offset(3), 0b11) };
|
||
|
|
// Enable FIFO.
|
||
|
|
unsafe { write_volatile(addr.offset(2), 0b1) };
|
||
|
|
// Enable receiver buffer interrupts.
|
||
|
|
unsafe { write_volatile(addr.offset(1), 0b1) };
|
||
|
|
}
|
||
|
|
|
||
|
|
// UART is now set up! Let's print a message.
|
||
|
|
for byte in "Hello, world!\n".bytes() {
|
||
|
|
unsafe { write_volatile(addr, byte) };
|
||
|
|
}
|
||
|
|
|
||
|
|
loop {}
|
||
|
|
}
|
||
|
|
|
||
|
|
#[panic_handler]
|
||
|
|
fn on_panic(_info: &PanicInfo) -> ! {
|
||
|
|
loop {}
|
||
|
|
}
|