Using it
Let's write a small program using our driver to write to the serial console, and echo incoming bytes.
#![no_main] #![no_std] mod exceptions; mod pl011; use crate::pl011::Uart; use core::fmt::Write; use core::panic::PanicInfo; use log::error; use smccc::psci::system_off; use smccc::Hvc; /// Base address of the primary PL011 UART. const PL011_BASE_ADDRESS: *mut u32 = 0x900_0000 as _; #[no_mangle] extern "C" fn main(x0: u64, x1: u64, x2: u64, x3: u64) { // SAFETY: `PL011_BASE_ADDRESS` is the base address of a PL011 device, and // nothing else accesses that address range. let mut uart = unsafe { Uart::new(PL011_BASE_ADDRESS) }; writeln!(uart, "main({x0:#x}, {x1:#x}, {x2:#x}, {x3:#x})").unwrap(); loop { if let Some(byte) = uart.read_byte() { uart.write_byte(byte); match byte { b'\r' => { uart.write_byte(b'\n'); } b'q' => break, _ => continue, } } } writeln!(uart, "\n\nBye!").unwrap(); system_off::<Hvc>().unwrap(); }
- As in the inline assembly example, this
main
function is called from our entry point code inentry.S
. See the speaker notes there for details. - Run the example in QEMU with
make qemu
undersrc/bare-metal/aps/examples
.