STM32F4xx HAL

https://github.com/stm32-rs/stm32f4xx-hal
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STM32F4xx-HAL is a multi-device hardware abstraction layer (HAL) for the STMicro STM32F4 series...
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### ADC Analog-to-Digital Conversion

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures ADC peripherals for reading analog voltages with configurable sample time and resolution. This example demonstrates reading analog input pins and converting the raw ADC values to millivolts.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{
    pac,
    prelude::*,
    adc::{Adc, config::{AdcConfig, SampleTime}},
};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::peripheral::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpioa = dp.GPIOA.split(&mut rcc);
    let gpiob = dp.GPIOB.split(&mut rcc);

    // Configure analog input pins
    let adc_pin = gpioa.pa0.into_analog();
    let adc_pin2 = gpiob.pb1.into_analog();

    // Create ADC with default configuration
    let mut adc = Adc::new(dp.ADC1, true, AdcConfig::default(), &mut rcc);

    // Get conversion function for millivolts
    let sample_to_mv = adc.make_sample_to_millivolts();

    let mut delay = cp.SYST.delay(&rcc.clocks);

    loop {
        // Read raw ADC value (12-bit, 0-4095)
        let raw_value: u16 = adc.convert(&adc_pin, SampleTime::Cycles_480);

        // Convert to millivolts
        let millivolts = sample_to_mv(raw_value);

        // Read another channel
        let raw_value2: u16 = adc.convert(&adc_pin2, SampleTime::Cycles_480);

        // Read internal temperature sensor
        // adc.enable_temperature_and_vref();
        // let temp_raw = adc.convert(&Temperature, SampleTime::Cycles_480);

        delay.delay_ms(100_u32);
    }
}

```

--------------------------------

### Configure and Feed Independent Watchdog

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Initializes the IWDG with a 1-second timeout and demonstrates the feed pattern within a main loop. Note that the watchdog cannot be stopped once started.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, watchdog::IndependentWatchdog};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::peripheral::Peripherals::take().unwrap();
    let rcc = dp.RCC.constrain();

    let gpioa = dp.GPIOA.split(&rcc);
    let mut led = gpioa.pa5.into_push_pull_output();
    let mut delay = cp.SYST.delay(&rcc.clocks);

    // Create watchdog with 1 second timeout
    let mut watchdog = IndependentWatchdog::new(dp.IWDG);
    watchdog.start(1000.millis());

    // Note: Once started, watchdog cannot be stopped!
    // System will reset if not fed within timeout period

    loop {
        led.toggle();
        delay.delay_ms(200_u32);

        // Feed the watchdog to prevent reset
        watchdog.feed();

        // If this line is commented out, system will reset after 1 second
    }
}
```

--------------------------------

### Configure SDIO for SD Card Interface

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Initializes the SDIO peripheral and an SD card for reading and writing. Requires the `sdio-host` feature. Ensure the SDIO peripheral is clocked at 48MHz.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{
    pac,
    prelude::*,
    rcc::Config,
    sdio::{ClockFreq, SdCard, Sdio},
};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::peripheral::Peripherals::take().unwrap();

    let mut rcc = dp.RCC.freeze(
        Config::hse(12.MHz())
            .require_pll48clk()  // SDIO requires 48MHz clock
            .sysclk(168.MHz())
    );

    let mut delay = cp.SYST.delay(&rcc.clocks);

    let gpioc = dp.GPIOC.split(&mut rcc);
    let gpiod = dp.GPIOD.split(&mut rcc);

    // Configure SDIO pins with internal pull-ups
    let d0 = gpioc.pc8.internal_pull_up(true);
    let d1 = gpioc.pc9.internal_pull_up(true);
    let d2 = gpioc.pc10.internal_pull_up(true);
    let d3 = gpioc.pc11.internal_pull_up(true);
    let clk = gpioc.pc12;
    let cmd = gpiod.pd2.internal_pull_up(true);

    // Create SDIO instance
    let mut sdio: Sdio<SdCard> = Sdio::new(
        dp.SDIO,
        (clk, cmd, d0, d1, d2, d3),
        &mut rcc
    );

    // Initialize card (retry until card detected)
    loop {
        match sdio.init(ClockFreq::F24Mhz) {
            Ok(_) => break,
            Err(_) => delay.delay_ms(100_u32),
        }
    }

    // Get card info
    if let Some(card) = sdio.card() {
        let _blocks = card.block_count();
    }

    // Read block 0 (boot sector)
    let mut buffer = [0u8; 512];
    sdio.read_block(0, &mut buffer).ok();

    // Write block (be careful with block 0!)
    // let write_data = [0xAAu8; 512];
    // sdio.write_block(1, &write_data).ok();

    loop {}
}

```

--------------------------------

### Dynamically Change GPIO Pin Modes

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Demonstrates changing GPIO pin modes at runtime between input and output. Uses a system timer for delays and requires `nb::block` for waiting.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use nb::block;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, gpio::PinState, timer::Timer};

#[entry]
fn main() -> ! {
    let cp = cortex_m::Peripherals::take().unwrap();
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpioc = dp.GPIOC.split(&mut rcc);

    // Create dynamic pin (mode can change at runtime)
    let mut pin = gpioc.pc13.into_dynamic();

    let mut timer = Timer::syst(cp.SYST, &rcc.clocks).counter_us();
    timer.start(1.secs()).unwrap();

    loop {
        // Switch to input mode and read
        pin.make_floating_input();
        block!(timer.wait()).unwrap();
        let _is_high = pin.is_high().unwrap();

        // Switch to output mode
        pin.make_push_pull_output_in_state(PinState::High);
        block!(timer.wait()).unwrap();

        pin.set_low().unwrap();
        block!(timer.wait()).unwrap();

        // Can also use pull-up/pull-down inputs
        pin.make_pull_up_input();
        block!(timer.wait()).unwrap();
    }
}

```

--------------------------------

### Configure GPIO Pins and Basic LED Blinking

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures GPIO pins for input/output operations and demonstrates basic LED control. Use for general-purpose input/output tasks and simple blinking patterns.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    // Split GPIO port into individual pins
    let gpioc = dp.GPIOC.split(&mut rcc);
    let gpioa = dp.GPIOA.split(&mut rcc);

    // Configure PC13 as push-pull output (common LED pin)
    let mut led = gpioc.pc13.into_push_pull_output();

    // Configure PA0 as floating input
    let button = gpioa.pa0.into_floating_input();

    // Configure PA1 as input with internal pull-up
    let _input_pullup = gpioa.pa1.into_pull_up_input();

    loop {
        // Read button state and control LED
        if button.is_high() {
            led.set_high();
        } else {
            led.set_low();
        }

        // Alternative: use toggle
        led.toggle();

        for _ in 0..100_000 {
            cortex_m::asm::nop();
        }
    }
}
```

--------------------------------

### Generate New Project with Template

Source: https://github.com/stm32-rs/stm32f4xx-hal/blob/master/README.md

Use the 'cargo generate' command with the stm32-template repository to quickly create a new Rust project for STM32 development. You will need to know the full name of your target chip.

```bash
$ cargo generate --git https://github.com/burrbull/stm32-template/

```

--------------------------------

### Add Dependencies to Cargo.toml

Source: https://github.com/stm32-rs/stm32f4xx-hal/blob/master/README.md

Include these dependencies in your Cargo.toml file to set up your project for stm32f4xx-hal development. Ensure the 'stm32f4xx-hal' version and features match your microcontroller and requirements.

```toml
[dependencies]
embedded-hal = "1.0"
b = "1"
cortex-m = "0.7"
cortex-m-rt = "0.7"
# Panic behaviour, see https://crates.io/keywords/panic-impl for alternatives
panic-halt = "1.0"

[dependencies.stm32f4xx-hal]
version = "0.23.0"
features = ["stm32f407"] # replace the model of your microcontroller here
                         # and add other required features

```

--------------------------------

### Configure DMA Transfers for SPI

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Initializes DMA streams for memory-to-peripheral data transfer. Uses a static buffer and configures SPI pins for high-speed operation.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use embedded_hal_02::spi::{Mode, Phase, Polarity};
use stm32f4xx_hal::{
    pac,
    prelude::*,
    gpio::Speed,
    spi::Spi,
    dma::{config::DmaConfig, MemoryToPeripheral, StreamsTuple, Transfer},
};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    // Initialize DMA streams
    let dma_streams = StreamsTuple::new(dp.DMA1, &mut rcc);
    let stream = dma_streams.4;  // DMA1 Stream 4

    let gpiob = dp.GPIOB.split(&mut rcc);

    // Configure SPI pins
    let mosi = gpiob.pb15.into_alternate().speed(Speed::VeryHigh);
    let sck = gpiob.pb13.into_alternate().speed(Speed::VeryHigh);

    let mode = Mode {
        polarity: Polarity::IdleLow,
        phase: Phase::CaptureOnFirstTransition,
    };

    let spi = Spi::new(
        dp.SPI2,
        (Some(sck), stm32f4xx_hal::pac::SPI2::NoMiso, Some(mosi)),
        mode,
        3.MHz(),
        &mut rcc,
    );

    // Get SPI TX for DMA
    let tx = spi.use_dma().tx();

    // Create static buffer for DMA
    let buffer = cortex_m::singleton!(: [u8; 100] = [0; 100]).unwrap();
    for (i, b) in buffer.iter_mut().enumerate() {
        *b = i as u8;
    }

    // Configure DMA transfer
    let dma_config = DmaConfig::default()
        .memory_increment(true)
        .fifo_enable(true)
        .transfer_complete_interrupt(true);

    let mut transfer = Transfer::init_memory_to_peripheral(
        stream,
        tx,
        buffer,
        None,
        dma_config,
    );

    // Start DMA transfer
    transfer.start(|_tx| {});

    // Wait for transfer completion
    while !transfer.flags().is_transfer_complete() {
        cortex_m::asm::nop();
    }

    loop {}
}
```

--------------------------------

### Configure USB CDC Serial Communication

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Sets up the USB OTG peripheral for virtual COM port communication. Requires the usb_fs feature and static memory allocation for USB endpoints.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use static_cell::ConstStaticCell;
use stm32f4xx_hal::{
    pac,
    prelude::*,
    rcc::Config,
    otg_fs::{UsbBus, USB},
};
use usb_device::prelude::*;

// USB endpoint memory (must be static)
static EP_MEMORY: ConstStaticCell<[u32; 1024]> = ConstStaticCell::new([0; 1024]);

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();

    // USB requires 48MHz clock from PLL
    let mut rcc = dp.RCC.freeze(
        Config::hse(25.MHz())
            .sysclk(48.MHz())
            .require_pll48clk()
    );

    let gpioa = dp.GPIOA.split(&mut rcc);

    // Configure USB peripheral (PA11=DM, PA12=DP)
    let usb = USB::new(
        (dp.OTG_FS_GLOBAL, dp.OTG_FS_DEVICE, dp.OTG_FS_PWRCLK),
        (gpioa.pa11, gpioa.pa12),
        &rcc.clocks,
    );

    let usb_bus = UsbBus::new(usb, EP_MEMORY.take());

    // Create CDC-ACM serial port
    let mut serial = usbd_serial::SerialPort::new(&usb_bus);

    // Build USB device
    let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27dd))
        .device_class(usbd_serial::USB_CLASS_CDC)
        .strings(&[StringDescriptors::default()
            .manufacturer("My Company")
            .product("Serial Port")
            .serial_number("001")])
        .unwrap()
        .build();

    let mut buf = [0u8; 64];

    loop {
        // Poll USB device
        if !usb_dev.poll(&mut [&mut serial]) {
            continue;
        }

        // Read data from host
        match serial.read(&mut buf) {
            Ok(count) if count > 0 => {
                // Echo back (convert to uppercase)
                for c in buf[0..count].iter_mut() {
                    if *c >= b'a' && *c <= b'z' {
                        *c -= 32;
                    }
                }
                serial.write(&buf[0..count]).ok();
            }
            _ => {}
        }
    }
}
```

--------------------------------

### Configure RTC for Timekeeping

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Initializes the RTC peripheral and sets the date and time. Requires the PWR peripheral to be passed during initialization.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, rtc::Rtc};
use time::{Date, Time, PrimitiveDateTime, Month};

#[entry]
fn main() -> ! {
    let mut dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    // Initialize RTC (requires PWR peripheral)
    let mut rtc = Rtc::new(dp.RTC, &mut rcc, &mut dp.PWR);

    let mut delay = dp.TIM5.delay_us(&mut rcc);

    // Set date and time
    let date = Date::from_calendar_date(2024, Month::January, 15).unwrap();
    let time = Time::from_hms(14, 30, 0).unwrap();
    let datetime = PrimitiveDateTime::new(date, time);
    rtc.set_datetime(&datetime).unwrap();

    // Alternative: set individual components
    // rtc.set_year(2024).unwrap();
    // rtc.set_month(1).unwrap();
    // rtc.set_day(15).unwrap();
    // rtc.set_hours(14).unwrap();
    // rtc.set_minutes(30).unwrap();
    // rtc.set_seconds(0).unwrap();

    loop {
        // Read current date/time
        let current = rtc.get_datetime();

        // Access individual components
        // let hours = current.hour();
        // let minutes = current.minute();
        // let seconds = current.second();

        delay.delay(1.secs());
    }
}
```

--------------------------------

### Configure SPI for Synchronous Serial Communication

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Sets up an SPI peripheral for synchronous serial communication. Configurable for clock polarity, phase, and speed.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use embedded_hal_02::spi::{Mode, Phase, Polarity};
use stm32f4xx_hal::{pac, prelude::*, gpio::Speed, spi::Spi};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpiob = dp.GPIOB.split(&mut rcc);

    // Configure SPI pins with appropriate speed
    let sck = gpiob.pb13.into_alternate().speed(Speed::VeryHigh);
    let miso = gpiob.pb14.into_alternate().speed(Speed::VeryHigh);
    let mosi = gpiob.pb15.into_alternate().speed(Speed::VeryHigh);

    // Optional: chip select pin
    let mut cs = gpiob.pb12.into_push_pull_output();
    cs.set_high();  // Deselect device

    let mode = Mode {
        polarity: Polarity::IdleLow,
        phase: Phase::CaptureOnFirstTransition,
    };

    // Create SPI instance
    let mut spi = Spi::new(
        dp.SPI2,
        (Some(sck), Some(miso), Some(mosi)),
        mode,
        3.MHz(),
        &mut rcc,
    );

    let tx_buffer: [u8; 4] = [0x01, 0x02, 0x03, 0x04];
    let mut rx_buffer: [u8; 4] = [0; 4];

    loop {
        cs.set_low();  // Select device

        // Transfer data (simultaneous read/write)
        spi.transfer(&mut rx_buffer, &tx_buffer).ok();

        cs.set_high();  // Deselect device

        for _ in 0..100_000 {
            cortex_m::asm::nop();
        }
    }
}
```

--------------------------------

### Configure PWM Output

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures timer channels for PWM output with adjustable frequency and duty cycle. Ensure the correct timer and GPIO pins are selected for your target microcontroller.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpioa = dp.GPIOA.split(&mut rcc);

    // Configure PWM with period of 100 microseconds (10kHz)
    let (_, (ch1, ch2, ..)) = dp.TIM1.pwm_us(100.micros(), &mut rcc);

    // Attach pins to PWM channels
    let mut pwm_ch1 = ch1.with(gpioa.pa8);
    let mut pwm_ch2 = ch2.with(gpioa.pa9);

    // Get maximum duty cycle value
    let max_duty = pwm_ch1.get_max_duty();

    // Set 50% duty cycle
    pwm_ch1.set_duty(max_duty / 2);

    // Set 25% duty cycle on channel 2
    pwm_ch2.set_duty(max_duty / 4);

    // Enable PWM output
    pwm_ch1.enable();
    pwm_ch2.enable();

    // Vary duty cycle for LED dimming effect
    loop {
        for duty in (0..=max_duty).step_by(100) {
            pwm_ch1.set_duty(duty);
            for _ in 0..10_000 {
                cortex_m::asm::nop();
            }
        }
        for duty in (0..=max_duty).rev().step_by(100) {
            pwm_ch1.set_duty(duty);
            for _ in 0..10_000 {
                cortex_m::asm::nop();
            }
        }
    }
}

```

--------------------------------

### Configure I2C for Inter-Integrated Circuit Communication

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Sets up an I2C peripheral for communication. Supports standard (100kHz) and fast (400kHz) speed modes for reading and writing data to devices.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, i2c::I2c};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpiob = dp.GPIOB.split(&mut rcc);

    // Configure I2C pins
    let scl = gpiob.pb8;  // I2C1 SCL
    let sda = gpiob.pb7;  // I2C1 SDA

    // Create I2C instance with standard mode (100kHz)
    let mut i2c = I2c::new(
        dp.I2C1,
        (scl, sda),
        stm32f4xx_hal::i2c::Mode::standard(100.kHz()),
        &mut rcc,
    );

    // For fast mode (400kHz):
    // let mut i2c = I2c::new(
    //     dp.I2C1,
    //     (scl, sda),
    //     stm32f4xx_hal::i2c::Mode::fast(400.kHz()),
    //     &mut rcc,
    // );

    const DEVICE_ADDR: u8 = 0x50;  // Example EEPROM address

    // Write data to device
    let write_data: [u8; 3] = [0x00, 0x01, 0x02];  // Address + data
    i2c.write(DEVICE_ADDR, &write_data).ok();

    // Read data from device
    let mut read_buffer: [u8; 2] = [0; 2];
    i2c.read(DEVICE_ADDR, &mut read_buffer).ok();

    // Write then read (write register address, read data)
    let reg_addr: [u8; 1] = [0x00];
    i2c.write_read(DEVICE_ADDR, &reg_addr, &mut read_buffer).ok();

    // I2C scanner - detect devices on bus
    for addr in 0x08_u8..0x78 {
        let probe: [u8; 1] = [0];
        if i2c.write(addr, &probe).is_ok() {
            // Device found at addr
        }
    }

    loop {}
}
```

--------------------------------

### Read Rotary Encoder with QEI

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures a timer as a Quadrature Encoder Interface to track rotation direction and position. Uses the embedded-hal Direction enum to determine rotation.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use embedded_hal_02::Direction;
use stm32f4xx_hal::{pac, prelude::*, qei::Qei};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::peripheral::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.constrain();

    let gpioa = dp.GPIOA.split(&mut rcc);
    let gpioc = dp.GPIOC.split(&mut rcc);

    let mut led = gpioc.pc13.into_push_pull_output();
    let mut delay = cp.SYST.delay(&rcc.clocks);

    // Connect rotary encoder to PA0 (A) and PA1 (B)
    let encoder_pins = (gpioa.pa0, gpioa.pa1);

    // Create QEI instance using TIM2
    let encoder = Qei::new(dp.TIM2, encoder_pins, &mut rcc);

    let mut last_count = encoder.count();

    loop {
        let current_count = encoder.count();

        if current_count != last_count {
            // Position changed
            let _diff = current_count.wrapping_sub(last_count) as i16;

            // Check rotation direction
            match encoder.direction() {
                Direction::Upcounting => led.set_low(),    // Clockwise
                Direction::Downcounting => led.set_high(), // Counter-clockwise
            }

            last_count = current_count;
        }

        delay.delay_ms(10_u32);
    }
}
```

--------------------------------

### Configure UART for Serial Communication

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Sets up a UART peripheral for serial communication with a configurable baud rate. Supports both transmit-only and full-duplex modes.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use core::fmt::Write;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, rcc::Config};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.freeze(Config::hse(25.MHz()));

    let gpioa = dp.GPIOA.split(&mut rcc);
    let mut delay = dp.TIM1.delay_ms(&mut rcc);

    // Configure TX pin (PA9 for USART1)
    let tx_pin = gpioa.pa9;
    let rx_pin = gpioa.pa10;

    // Create TX-only serial port
    let mut tx = dp.USART1.tx(tx_pin, 115200.bps(), &mut rcc).unwrap();

    // Or create full duplex serial
    let mut serial = dp.USART1.serial(
        (tx_pin, rx_pin),
        115200.bps(),
        &mut rcc
    ).unwrap();

    let mut counter: u8 = 0;

    loop {
        // Write formatted output
        writeln!(tx, "Counter: \r", counter).unwrap();

        // Write raw bytes
        tx.write_byte(0x41).ok();  // Write 'A'

        // Read with serial (blocking)
        // if let Ok(byte) = nb::block!(serial.read()) {
        //     nb::block!(serial.write(byte)).ok();
        // }

        counter = counter.wrapping_add(1);
        delay.delay(1.secs());
    }
}
```

--------------------------------

### Communicate via CAN Bus

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Sets up CAN peripheral communication using the bxcan crate. Requires an external crystal for clock accuracy and specific bit timing configuration.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use bxcan::{filter::Mask32, Fifo, Frame, StandardId};
use nb::block;
use stm32f4xx_hal::{pac, prelude::*, rcc::Config};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();

    // CAN requires external crystal for clock accuracy
    let mut rcc = dp.RCC.freeze(Config::hse(8.MHz()));

    let gpiob = dp.GPIOB.split(&mut rcc);

    // Configure CAN1 pins (PB8=RX, PB9=TX)
    let rx = gpiob.pb8;
    let tx = gpiob.pb9;

    // Initialize CAN peripheral
    let can = dp.CAN1.can((tx, rx), &mut rcc);

    // Configure and enable CAN
    let mut can = bxcan::Can::builder(can)
        // Bit timing for 500kbit/s at 8MHz APB1
        // Calculate at http://www.bittiming.can-wiki.info/
        .set_bit_timing(0x001c_0000)
        .enable();

    // Configure acceptance filters
    let mut filters = can.modify_filters();
    filters.enable_bank(0, Fifo::Fifo0, Mask32::accept_all());
    drop(filters);

    let mut data: [u8; 8] = [0; 8];
    let id: u16 = 0x500;

    loop {
        // Create and send CAN frame
        data[0] = data[0].wrapping_add(1);
        let frame = Frame::new_data(StandardId::new(id).unwrap(), data);
        block!(can.transmit(&frame)).unwrap();

        // Receive frames
        // if let Ok(frame) = can.receive() {
        //     // Process received frame
        // }

        for _ in 0..100_000 {
            cortex_m::asm::nop();
        }
    }
}
```

--------------------------------

### Create Blocking Delays Using Timers

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Implements blocking delays using the SysTick timer or hardware timers. Useful for creating precise timing intervals in embedded applications.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, rcc::Config};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::peripheral::Peripherals::take().unwrap();

    let mut rcc = dp.RCC.freeze(Config::hsi().sysclk(48.MHz()));
    let gpioa = dp.GPIOA.split(&mut rcc);
    let mut led = gpioa.pa5.into_push_pull_output();

    // Create delay using SysTick
    let mut delay = cp.SYST.delay(&rcc.clocks);

    // Alternative: use hardware timer for delay
    let mut timer_delay = dp.TIM1.delay_ms(&mut rcc);

    loop {
        led.toggle();
        delay.delay_ms(500_u32);  // 500ms delay

        led.toggle();
        delay.delay_us(100_000_u32);  // 100ms in microseconds

        // Using hardware timer delay
        timer_delay.delay(1.secs());
    }
}
```

--------------------------------

### Configure Timer Interrupts

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures hardware timers to generate periodic interrupts for time-critical operations. Global mutable static variables are used to share peripherals between the main function and the interrupt handler, protected by mutexes.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use core::cell::RefCell;
use cortex_m::interrupt::Mutex;
use cortex_m_rt::entry;
use stm32f4xx_hal::{
    pac::{self, interrupt, Interrupt, TIM2},
    prelude::*,
    rcc::Config,
    gpio::{Output, PushPull, PA5},
    timer::{CounterUs, Event},
};

// Global state protected by mutex
static G_LED: Mutex<RefCell<Option<PA5<Output<PushPull>>>>> = Mutex::new(RefCell::new(None));
static G_TIM: Mutex<RefCell<Option<CounterUs<TIM2>>>> = Mutex::new(RefCell::new(None));

#[interrupt]
fn TIM2() {
    static mut LED: Option<PA5<Output<PushPull>>> = None;
    static mut TIM: Option<CounterUs<TIM2>> = None;

    let led = LED.get_or_insert_with(|| {
        cortex_m::interrupt::free(|cs| G_LED.borrow(cs).replace(None).unwrap())
    });

    let tim = TIM.get_or_insert_with(|| {
        cortex_m::interrupt::free(|cs| G_TIM.borrow(cs).replace(None).unwrap())
    });

    led.toggle();
    let _ = tim.wait();  // Clear interrupt flag
}

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let mut rcc = dp.RCC.freeze(Config::hsi().sysclk(16.MHz()).pclk1(8.MHz()));

    let gpioa = dp.GPIOA.split(&mut rcc);
    let led = gpioa.pa5.into_push_pull_output();

    // Move LED to global storage
    cortex_m::interrupt::free(|cs| *G_LED.borrow(cs).borrow_mut() = Some(led));

    // Configure timer for 1 second period
    let mut timer = dp.TIM2.counter(&mut rcc);
    timer.start(1.secs()).unwrap();
    timer.listen(Event::Update);  // Enable update interrupt

    // Move timer to global storage
    cortex_m::interrupt::free(|cs| *G_TIM.borrow(cs).borrow_mut() = Some(timer));

    // Enable TIM2 interrupt in NVIC
    unsafe {
        cortex_m::peripheral::NVIC::unmask(Interrupt::TIM2);
    }

    loop {
        cortex_m::asm::wfi();  // Wait for interrupt
    }
}

```

--------------------------------

### Configure RCC Clock System

Source: https://context7.com/stm32-rs/stm32f4xx-hal/llms.txt

Configures the Reset and Clock Control (RCC) system for various clock sources and frequencies. Use to set up the system clock, including options for HSI, HSE, and PLL configurations.

```rust
#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f4xx_hal::{pac, prelude::*, rcc::Config};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();

    // Option 1: Use HSI (internal) oscillator with default settings
    let mut rcc = dp.RCC.constrain();

    // Option 2: Configure HSI with specific system clock
    let mut rcc = dp.RCC.freeze(Config::hsi().sysclk(48.MHz()));

    // Option 3: Use HSE (external) oscillator (e.g., 25MHz crystal)
    let mut rcc = dp.RCC.freeze(Config::hse(25.MHz()));

    // Option 4: Full configuration with PLL
    let mut rcc = dp.RCC.freeze(
        Config::hse(25.MHz())
            .sysclk(168.MHz())
            .hclk(168.MHz())
            .pclk1(42.MHz())
            .pclk2(84.MHz())
            .require_pll48clk()  // Required for USB/SDIO
    );

    // Access clock frequencies
    let _sysclk = rcc.clocks.sysclk();
    let _pclk1 = rcc.clocks.pclk1();

    loop {}
}
```
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