rust-embedded

no_std basics

#![no_std]
// 不能使用 std, alloc, test

use core::panic::PanicMessage;

// 必须实现 panic handler
#[panic_handler]
fn panic(info: &PanicMessage) -> ! {
    loop {}
}

// 可选：定义全局分配器
#[global_allocator]
static ALLOC: some_allocator::Allocator = some_allocator::Allocator;

Available modules

Module	Purpose
core	Basic language features
alloc	Heap allocation (requires allocator)
compiler_builtins	Compiler intrinsics

embedded-hal

use embedded_hal as hal;
use hal::digital::v2::OutputPin;

// 抽象硬件访问
fn blink_led<L: OutputPin>(mut led: L) -> ! {
    loop {
        led.set_high().unwrap();
        delay_ms(1000);
        led.set_low().unwrap();
        delay_ms(1000);
    }
}

Common traits

trait	Operation
OutputPin	Set high/low level
InputPin	Read pin
SpiBus	SPI communication
I2c	I2C communication
Serial	Serial port

Interrupt handling

#![no_std]
#![feature(abi_vectorcall)]

use cortex_m::interrupt::{free, Mutex};
use cortex_m::peripheral::NVIC;

// 共享状态
static MY_DEVICE: Mutex<Cell<Option<MyDevice>>> = Mutex::new(None);

#[interrupt]
fn TIM2() {
    free(|cs| {
        let device = MY_DEVICE.borrow(cs).take();
        if let Some(dev) = device {
            // 处理中断
            dev.handle();
            MY_DEVICE.borrow(cs).set(Some(dev));
        }
    });
}

// 启用中断
fn enable_interrupt(nvic: &mut NVIC, irq: interrupt::TIM2) {
    nvic.enable(irq);
}

Memory management

Stack size

[profile.dev]
panic = "abort"  # 减少二进制大小

[profile.release]
lto = true
opt-level = "z"  # 最小化大小

Avoid dynamic allocation

// 用栈数组代替 Vec
let buffer: [u8; 256] = [0; 256];

// 或使用定长环形缓冲区
struct RingBuffer {
    data: [u8; 256],
    write_idx: usize,
    read_idx: usize,
}

Peripheral access patterns

// 寄存器映射
const GPIOA_BASE: *const u32 = 0x4002_0000 as *const u32;
const GPIOA_ODR: *const u32 = (GPIOA_BASE + 0x14) as *const u32;

// 安全抽象
mod gpioa {
    use super::*;
    
    pub fn set_high() {
        unsafe {
            GPIOA_ODR.write_volatile(1 << 5);
        }
    }
}

Common problems

Problem	Cause	Solution
panic infinite loop	No panic handler	Implement #[panic_handler]
Stack overflow	Nested interrupts or large local variables	Increase stack, reduce local variables
Memory corruption	Raw pointer operations	Use safe abstraction
Program does not run	Linker script problem	Check startup code
Peripheral not responding	Clock not enabled	Configure RCC first

Resource-constrained techniques

Technique	Effect
opt-level = "z"	Minimize size
lto = true	Link-time optimization
panic = "abort"	Remove unwinding
codegen-units = 1	Better optimization
Avoid alloc	Use stack or static arrays

Project configuration example

[package]
name = "my-firmware"
version = "0.1.0"
edition = "2024"

[dependencies]
cortex-m = "0.7"
cortex-m-rt = "0.7"
embedded-hal = "1.0"
nb = "1.0"

[profile.dev]
panic = "abort"

[profile.release]
opt-level = "z"
lto = true
codegen-units = 1

WebAssembly multithreading

SharedArrayBuffer

// 需要在服务器端配置 Cross-Origin-Opener-Policy
// 浏览器才能使用 SharedArrayBuffer

// wasm-bindgen 配置
[dependencies]
wasm-bindgen = { version = "0.2", features = ["enable-threads"] }

// 使用 atomic 内存序
use std::sync::atomic::{AtomicUsize, Ordering};

static COUNTER: AtomicUsize = AtomicUsize::new(0);

#[wasm_bindgen]
pub fn increment_counter() -> usize {
    COUNTER.fetch_add(1, Ordering::SeqCst)
}

#[wasm_bindgen]
pub fn get_counter() -> usize {
    COUNTER.load(Ordering::SeqCst)
}

Atomics and memory ordering

use std::sync::atomic::{AtomicI32, Ordering};

// 不同内存序的性能和可见性权衡
#[wasm_bindgen]
pub fn atomic_demo() {
    let atom = AtomicI32::new(0);
    
    // 最强保证，最慢
    atom.store(1, Ordering::SeqCst);
    
    // 释放语义（生产者）
    atom.store(2, Ordering::Release);
    
    // 获取语义（消费者）
    let val = atom.load(Ordering::Acquire);
    
    // 松散语义，最快，但可能 reordered
    atom.store(3, Ordering::Relaxed);
    let val = atom.load(Ordering::Relaxed);
}

Thread-local storage (TLS)

// WASM 线程局部存储
use std::cell::RefCell;

thread_local! {
    static THREAD_ID: RefCell<u32> = RefCell::new(0);
}

#[wasm_bindgen]
pub fn set_thread_id(id: u32) {
    THREAD_ID.with(|tid| {
        *tid.borrow_mut() = id;
    });
}

#[wasm_bindgen]
pub fn get_thread_id() -> u32 {
    THREAD_ID.with(|tid| *tid.borrow())
}

RISC-V embedded development

Basic setup

// Cargo.toml
[package]
name = "riscv-firmware"
version = "0.1.0"
edition = "2024"

[dependencies]
riscv = "0.10"
embedded-hal = "1.0"

[profile.release]
opt-level = "z"
lto = true

Interrupts and exceptions

// RISC-V 中断处理
#![no_std]

use riscv::register::{
    mie::MIE,
    mstatus::MSTATUS,
    mip::MIP,
};

/// 启用机器中断
pub fn enable_interrupt() {
    // 启用外部中断、计时器中断、软件中断
    unsafe {
        MIE::set_mext();
        MIE::set_mtimer();
        MIE::set_msip();
        
        // 全局中断使能
        MSTATUS::set_mie();
    }
}

/// 禁用所有中断
pub fn disable_interrupt() {
    unsafe {
        MSTATUS::clear_mie();
    }
}

Memory barriers

// RISC-V 内存屏障
use riscv::asm;

/// 数据内存屏障 - 确保所有内存访问完成
fn data_memory_barrier() {
    unsafe {
        asm!("fence iorw, iorw");
    }
}

/// 指令屏障 - 确保指令流更新可见
fn instruction_barrier() {
    unsafe {
        asm!("fence i, i");
    }
}

Atomic operations

// 使用 riscv::atomic 模块
use riscv::asm::atomic;

fn atomic_add(dst: &mut usize, val: usize) {
    unsafe {
        // 使用 amoadd.w 指令
        atomic::amoadd(dst as *mut usize, val);
    }
}

fn compare_and_swap(ptr: &mut usize, old: usize, new: usize) -> bool {
    unsafe {
        // 使用 amoswap.w 指令
        let current = atomic::amoswap(ptr as *mut usize, new);
        current == old
    }
}

Multicore synchronization

// RISC-V 机器间中断 (IPI)
const M_SOFT_INT: *mut u32 = 0x3FF0_FFF0 as *mut u32;

fn send_soft_interrupt(core_id: u32) {
    unsafe {
        // 设置软件中断位
        M_SOFT_INT.write_volatile(1 << core_id);
    }
}

fn clear_soft_interrupt(core_id: u32) {
    unsafe {
        M_SOFT_INT.write_volatile(0);
    }
}

RISC-V privilege levels

// RISC-V 特权级检查
use riscv::register::{mstatus, misa};

fn check_privilege_level() -> u8 {
    // 读取当前特权级
    // 0 = User, 1 = Supervisor, 2 = Hypervisor, 3 = Machine
    (mstatus::read().bits() >> 11) & 0b11
}

fn is_machine_mode() -> bool {
    check_privilege_level() == 3
}

/// 获取可用的 ISA 扩展
fn get_isa_extensions() -> String {
    let misa = misa::read();
    format!("{:?}", misa)
}

RISC-V performance optimization

Optimization point	Method
Memory access	Use unaligned access instructions (if supported)
Atomic operations	Use A extension instructions
Multiplication and division	Use M extension instructions
Vector operations	Use V extension (RV64V)
Compressed instructions	Use C extension to reduce code size