rust-raspberrypi-OS-tutorials/.03_uart1/README.md

Tutorial 03 - UART1, Auxilary mini UART

It is time for the famous Hello World example. We're going to write on the UART1 first, as it is easier to program, since it has a fixed clocked frequency.

gpio.rs

We have a new file that defines the GPIO controller addresses. It is going to be very popular, as many device will need it in the future.

We are using the register crate to modify MMIO addresses, because it allows easy wrapping of addresses to volatile types. It will also be used for UART registers.

uart.rs

A very minimal implementation.

MiniUart::init(&self) initializes the device and maps it to the GPIO ports.

MiniUart::send(&self, c: char) sends a character over the serial line.

MiniUart::getc(&self) receives a character. The carrige return character (13) will be converted into a newline character (10).

MiniUart::puts(&self, string: &str) prints out a string. On newline, a carrige return character will also be sent (13 + 10).

main.rs

First, we have to call the uart initialization code. Then we wait for the first keypress from the user before we say "Hello Rustacean!". If you've purchased an USB serial cable, you should see it on screen's screen. After that, every character typed in screen will be echoed back. If you haven't turned off local echo, that means you'll see every pressed key twice.

Simulation

We can also use QEMU to simulate the UART output of our bare-metal binary on the host PC.

ferris@box:~$ make qemu
[0] UART is live!
[1] Press a key to continue booting... Greetings fellow Rustacean!

However, let it be said that it is more thrilling to see your first output from the real hardware target, so don't be shy and grab a USB-serial.