实战：异步环境监测节点

项目目标与用到的知识

这个"环境监测节点"每 2 秒读一次温湿度、通过串口上报、用 LED 显示健康状态、按键可切换上报频率。它把整套 Rust 嵌入式技艺串起来：

系统架构图

Cargo.toml

# 目标 STM32F411（Black Pill）；换芯片改 embassy-stm32 的 feature
[package]
name = "env-node"
version = "0.1.0"
edition = "2021"

[dependencies]
embassy-executor = { version = "0.6", features = ["arch-cortex-m", "executor-thread", "integrated-timers"] }
embassy-time     = { version = "0.3", features = ["tick-hz-32_768"] }
embassy-stm32    = { version = "0.1", features = ["stm32f411ce", "time-driver-any", "exti", "memory-x", "unstable-pac"] }
embassy-sync     = "0.6"
embassy-futures  = "0.1"

# 日志与 panic（第 11 章）
defmt        = "0.3"
defmt-rtt    = "0.4"
panic-probe  = { version = "0.3", features = ["print-defmt"] }

# 无堆动态集合（第 9 章）
heapless = "0.8"

# async HAL trait（第 4 章）
embedded-hal-async = "1.0"

[profile.release]
opt-level = "s"      # 优化体积
lto = true
debug = 2          # 保留符号供 defmt 解码，不进最终 Flash

主程序：三任务协作

#![no_std]
#![no_main]
use defmt_rtt as _;
use panic_probe as _;
use core::fmt::Write;
use heapless::String;
use embassy_executor::Spawner;
use embassy_time::{Timer, Duration};
use embassy_sync::{blocking_mutex::raw::ThreadModeRawMutex, channel::Channel, signal::Signal};
use embassy_stm32::{gpio::{Level, Output, Speed, Input, Pull}, i2c::I2c, usart::Uart, exti::ExtiInput};

// 一条温湿度读数
#[derive(Clone, Copy, defmt::Format)]
struct Reading { temp_c: f32, hum_pct: f32 }

// 任务间通信原语：静态分配、无堆
static CHAN: Channel<ThreadModeRawMutex, Reading, 4> = Channel::new();
static PERIOD: Signal<ThreadModeRawMutex, u64> = Signal::new();

// —— sensor 任务：按周期读 I2C，发进 Channel ——
#[embassy_executor::task]
async fn sensor_task(mut i2c: I2c<'static, embassy_stm32::mode::Async>) {
    let mut period_ms: u64 = 2000;
    loop {
        // 若 ui 改了周期，取最新值（非阻塞判断）
        if let Some(p) = PERIOD.try_take() { period_ms = p; }

        let mut buf = [0u8; 6];
        // SHT3x：发测量命令 0x2400，读 6 字节（温+湿+CRC）
        match i2c.write_read(0x44, &[0x24, 0x00], &mut buf).await {
            Ok(()) => {
                let raw_t = u16::from_be_bytes([buf[0], buf[1]]);
                let raw_h = u16::from_be_bytes([buf[3], buf[4]]);
                let reading = Reading {
                    temp_c: -45.0 + 175.0 * raw_t as f32 / 65535.0,
                    hum_pct: 100.0 * raw_h as f32 / 65535.0,
                };
                CHAN.send(reading).await;   // 满则挂起等消费
            }
            Err(e) => defmt::warn!("i2c read failed: {:?}", defmt::Debug2Format(&e)),
        }
        Timer::after(Duration::from_millis(period_ms)).await;  // 挂起,期间可睡眠
    }
}

// —— report 任务：收数据，格式化后串口发出 ——
#[embassy_executor::task]
async fn report_task(mut uart: Uart<'static, embassy_stm32::mode::Async>) {
    loop {
        let r = CHAN.receive().await;          // 空则挂起等数据
        let mut line: String<32> = String::new();
        let _ = write!(line, "T={=f32},H={=f32}\r\n", r.temp_c, r.hum_pct);
        let _ = uart.write(line.as_bytes()).await;  // DMA 发送,不占 CPU
        defmt::info!("reported {:?}", r);
    }
}

// —— ui 任务：按键切周期 + LED 状态 ——
#[embassy_executor::task]
async fn ui_task(mut button: ExtiInput<'static>, mut led: Output<'static>) {
    let periods = [2000u64, 5000, 10000];
    let mut idx = 0;
    loop {
        button.wait_for_falling_edge().await;   // 挂起等按键
        idx = (idx + 1) % periods.len();
        PERIOD.signal(periods[idx]);           // 通知 sensor 任务
        led.toggle();
        defmt::info!("period -> {} ms", periods[idx]);
        Timer::after(Duration::from_millis(50)).await;  // 消抖
    }
}

#[embassy_executor::main]
async fn main(spawner: Spawner) {
    let p = embassy_stm32::init(Default::default());

    // 初始化外设（时钟/引脚配置随芯片,此处示意）
    let led = Output::new(p.PC13, Level::High, Speed::Low);
    let button = ExtiInput::new(p.PA0, p.EXTI0, Pull::Up);
    let i2c = /* I2c::new(...) 配 PB6/PB7 + DMA */ todo!();
    let uart = /* Uart::new(...) 配 PA9/PA10 + DMA */ todo!();

    // 启动三个并发任务；它们各自 await,空闲时 CPU 睡眠
    spawner.spawn(sensor_task(i2c)).unwrap();
    spawner.spawn(report_task(uart)).unwrap();
    spawner.spawn(ui_task(button, led)).unwrap();
}

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