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UART - Part 2

Consider our boilerplate:

#![no_std]
#![no_main]
use esp_hal::{main, Config};
use esp_backtrace as _;
use esp_println as _;
esp_bootloader_esp_idf::esp_app_desc!();

#[main]
fn main() -> ! {
  let peripherals = esp_hal::init(Config::default())
  loop {}
}

How do we get to use a UART peripheral from there? How do we configure the peripheral? Which configuration options do you expect? Try getting a sense of what to do first (maybe checking esp_hal docs.)

Warning

The pinouts won't help. UART is connected to UART-USB bridge (a small IC near the USB ports). So when passing the with_rx and with_tx to the driver, we must choose the GPIOs hardwired to the UART-USB bridge. These are GPIO16, GPIO17. For sending to GPIO-header-pins (those on the sidelines) we could pass any GPIO (but not when using the bridge.)

======!Spoiler Alert!====== (click for a solution)

There are many other details in the main.rs file, but the most critical is to make sense of this snippet:

let uart_config = uart::Config::default()
    .with_baudrate(115200)
    // ... other settings

let mut uart = Uart::new(peripherals.UART0, uart_config)
    //   driver^^^^^^^^^       periph^^^^^ config^^^^^^
    .expect("Should set up the driver.")
    // Route through the UART-USB bridge
    .with_tx(peripherals.GPIO16)
    .with_rx(peripherals.GPIO17);

That is another boilerplate we can think of: init device, grab peripheral, pass it to a driver along with its config.

A list of some of the peripherals is:

# (Most of these are unstable)
GPIO0-23, GPIO27 peripheral singleton
I2C0 peripheral singleton
I2S0 peripheral singleton
LEDC peripheral singleton
RNG peripheral singleton
SPI0-2 peripheral singleton
TIMG0-1 peripheral singleton
UART0-1 peripheral singleton
USB_DEVICE peripheral singleton
WIFI peripheral singleton

Exercise

  1. Access exercises/uart/src/main.rs. The comments within will guide you through.
  2. If not installed install screen (for example sudo apt install screen).
  3. Before running it, note that we exit screen with Ctrl+a+k (then pressing y when prompted for it).
  4. After flashing the board (any USB port) connect it through ch343 (or UART) tagged port.
  5. Run screen <device_path> <baud_rate>.
    • <device_path> is probably /dev/ttyACM0 on Linux and /dev/tty.usbmodem0 MacOS.
    • To be sure, list them with ls /dev/tty* and try to figure out which one is the board.
    • <baud_rate> must match the rate in the code. For example 115200.
  6. Remember to press the RESET board button once.
  7. Try the echo server by typing in the keyboard, and send with Enter key.

Note

A solution is provided in examples/uart.rs.

Imagining a projects

The esp32-c6 board has 2 UARTs: UART0 and UART1.

Technically, we could use UART0 just as we did, and UART1 could other GPIOs connected to GPIO-header-pins. By linking this to USB-UART converter and this in turn to a laptop, we could chat.

Two laptops could chat via the board.

Suggested Reading

  • This is a good time to check esp_hal, especially their peripherals section, and anything you find interesting.