Add SPI example using embedded_hal_bus

rp2040-hal-examples/Cargo.toml

@@ -22,6 +22,7 @@ dht-sensor = "0.2.1"
 embedded-alloc = "0.5.1"
 embedded-hal = "1.0.0"
 embedded-hal-async = "1.0.0"
+embedded-hal-bus = {version = "0.2.0", features = ["defmt-03"]}
 embedded-io = "0.6.1"
 embedded_hal_0_2 = {package = "embedded-hal", version = "0.2.5", features = ["unproven"]}
 fugit = "0.3.6"
@@ -33,5 +34,8 @@ panic-halt = "0.2.0"
 panic-probe = {version = "0.3.1", features = ["print-defmt"]}
 pio = "0.2.0"
 pio-proc = "0.2.0"
+# We aren't using this, but embedded-hal-bus 0.2 unconditionally requires atomics.
+# Should be fixed in e-h-b 0.3 via https://github.com/rust-embedded/embedded-hal/pull/607
+portable-atomic = {version = "1.7.0", features = ["critical-section"]}
 rp2040-boot2 = "0.3.0"
 rp2040-hal = {path = "../rp2040-hal", version = "0.10.0", features = ["binary-info", "critical-section-impl", "rt", "defmt"]}

rp2040-hal-examples/src/bin/spi.rs

@@ -78,7 +78,7 @@ fn main() -> ! {
         &mut pac.RESETS,
     );
 
-    // These are implicitly used by the spi driver if they are in the correct mode
+    // Set up our SPI pins so they can be used by the SPI driver
     let spi_mosi = pins.gpio7.into_function::<hal::gpio::FunctionSpi>();
     let spi_miso = pins.gpio4.into_function::<hal::gpio::FunctionSpi>();
     let spi_sclk = pins.gpio6.into_function::<hal::gpio::FunctionSpi>();

rp2040-hal-examples/src/bin/spi_eh_bus.rs

@@ -0,0 +1,307 @@
+//! # SPI Bus example
+//!
+//! This application demonstrates how to construct a simple SPI Driver and
+//! configure rp2040-hal's SPI peripheral to access it by utilising
+//! [`ExclusiveDevice`] from [`embedded-hal-bus`].
+//!
+//! [`ExclusiveDevice`]:
+//!     https://docs.rs/embedded-hal-bus/latest/embedded_hal_bus/spi/struct.ExclusiveDevice.html
+//! [`embedded-hal-bus`]: https://crates.io/crates/embedded-hal-bus
+//!
+//! It may need to be adapted to your particular board layout and/or pin
+//! assignment.
+//!
+//! See the top-level `README.md` file for Copyright and license details.
+//!
+//! ## Glossary
+//!
+//! * *SPI Bus* - a shared bus consisting of three shared wires (Clock, COPI and
+//!   CIPO) and a unique 'Chip Select' wire for each device on the bus. An *SPI
+//!   Bus* typically only has one *SPI Controller* which is 'driving' the bus
+//!   (specifically it is driving the clock signal and the *COPI* data line).
+//! * *COPI* - One of the data lines on an *SPI Bus*. Stands for *Controller
+//!   Out, Peripheral In*, but we use the term *SPI Device* instead of *SPI
+//!   Peripheral*.
+//! * *CIPO* - One of the data lines on an *SPI Bus*. Stands for *Controller In,
+//!   Peripheral Out*, but we use the term *SPI Device* instead of *SPI
+//!   Peripheral*.
+//! * *SPI Controller* - a block of silicon within the RP2040 designed for
+//!   driving an *SPI Bus*.
+//! * *SPI Device* - a device on the *SPI Bus*; has its own unique chip select
+//!   signal.
+//! * *Device Driver* - a Rust type (and/or a value of that type) which
+//!   represents a particular *SPI Device*, such as an Bosch BMA400
+//!   accelerometer chip, or an ST7789 LCD controller chip.
+
+#![no_std]
+#![no_main]
+
+// Ensure we halt the program on panic (if we don't mention this crate it won't
+// be linked)
+use panic_halt as _;
+
+// Alias for our HAL crate
+use rp2040_hal as hal;
+
+// Some types/traits we need
+use core::fmt::Write;
+use embedded_hal::spi::Operation;
+use embedded_hal::spi::SpiDevice;
+use embedded_hal_bus::spi::ExclusiveDevice;
+use hal::clocks::Clock;
+use hal::fugit::RateExtU32;
+use hal::gpio::PinState;
+use hal::uart::{DataBits, StopBits, UartConfig};
+
+/// The linker will place this boot block at the start of our program image. We
+/// need this to help the ROM bootloader get our code up and running.
+/// Note: This boot block is not necessary when using a rp-hal based BSP
+/// as the BSPs already perform this step.
+#[link_section = ".boot2"]
+#[used]
+pub static BOOT2: [u8; 256] = rp2040_boot2::BOOT_LOADER_GENERIC_03H;
+
+/// External high-speed crystal on the Raspberry Pi Pico board is 12 MHz. Adjust
+/// if your board has a different frequency
+const XTAL_FREQ_HZ: u32 = 12_000_000u32;
+
+/// The ways our device driver might fail.
+///
+/// When things go wrong, we could return `Err(())`` but that wouldn't help
+/// anyone troubleshoot so we'll create an error type with additional info to
+/// return.
+#[derive(Copy, Clone, Debug)]
+pub enum MyError<E> {
+    /// We got an error from the *SPI Device*
+    Spi(E),
+    // Add other errors for your driver here.
+}
+
+/// Our *Device Driver* type.
+///
+/// This is an example of a device driver that manages some kind of *SPI
+/// Device*.
+///
+/// It is not a driver for any real device - it's here as an example of how to
+/// write such a driver. You would typically get real drivers from a library
+/// crate but we've pasted it into the example so you can see it.
+///
+/// We need to use a generic here (`SD`), because we want our example
+/// driver to work for any other microcontroller that implements the
+/// embedded-hal SPI traits - specifically the `embedded_hal::spi::SpiDevice`
+/// trait that represents access to a unique device on the bus.
+pub struct MySpiDeviceDriver<SD> {
+    spi_dev: SD,
+}
+
+impl<SD> MySpiDeviceDriver<SD>
+where
+    SD: SpiDevice,
+{
+    /// Construct a new instance of our *Device Driver*.
+    ///
+    /// Takes ownership of a value representing a unique device on the *SPI
+    /// Bus*.
+    pub fn new(spi_dev: SD) -> Self {
+        Self { spi_dev }
+    }
+
+    /// Write to our hypothetical device.
+    ///
+    /// We imagine our device has a register at `0x20`, that accepts a `u8`
+    /// value.
+    pub fn set_value(&mut self, value: u8) -> Result<(), MyError<SD::Error>> {
+        self.spi_dev
+            .transaction(&mut [Operation::Write(&[0x20, value])])
+            .map_err(MyError::Spi)?;
+
+        Ok(())
+    }
+
+    /// Read from our hypothetical device.
+    ///
+    /// We imagine our device has a register at `0x90`, that we can read a 2
+    /// byte integer value from.
+    pub fn get_value(&mut self) -> Result<u16, MyError<SD::Error>> {
+        let mut buf = [0u8; 2];
+        self.spi_dev
+            .transaction(&mut [Operation::Write(&[0x90]), Operation::Read(&mut buf)])
+            .map_err(MyError::Spi)?;
+
+        Ok(u16::from_le_bytes(buf))
+    }
+}
+
+/// Entry point to our bare-metal application.
+///
+/// The `#[rp2040_hal::entry]` macro ensures the Cortex-M start-up code calls
+/// this function as soon as all global variables and the spinlock are
+/// initialised.
+///
+/// The function configures the RP2040 peripherals, then performs some example
+/// SPI transactions, then goes to sleep.
+#[rp2040_hal::entry]
+fn main() -> ! {
+    // ========================================================================
+    // Some things that pretty much every rp2040-hal program will do
+    // ========================================================================
+
+    // Grab our singleton objects
+    let mut p = hal::pac::Peripherals::take().unwrap();
+
+    // Set up the watchdog driver - needed by the clock setup code
+    let mut watchdog = hal::Watchdog::new(p.WATCHDOG);
+
+    // Configure the clocks
+    let clocks = hal::clocks::init_clocks_and_plls(
+        XTAL_FREQ_HZ,
+        p.XOSC,
+        p.CLOCKS,
+        p.PLL_SYS,
+        p.PLL_USB,
+        &mut p.RESETS,
+        &mut watchdog,
+    )
+    .unwrap();
+
+    // The single-cycle I/O block controls our GPIO pins
+    let sio = hal::Sio::new(p.SIO);
+
+    // Set the pins to their default state
+    let pins = hal::gpio::Pins::new(p.IO_BANK0, p.PADS_BANK0, sio.gpio_bank0, &mut p.RESETS);
+
+    // ========================================================================
+    // Construct a timer object, which we will need later.
+    // ========================================================================
+
+    let timer = hal::Timer::new(p.TIMER, &mut p.RESETS, &clocks);
+
+    // ========================================================================
+    // Set up a UART so we can print out the values we read using our *Device
+    // Driver*:
+    // ========================================================================
+
+    // How we want our UART to be configured
+    let uart_config = UartConfig::new(115200.Hz(), DataBits::Eight, None, StopBits::One);
+
+    // The pins we want to use for our UART.
+    let uart_pins = (
+        // UART TX (characters sent from RP2040) on pin 1 (GPIO0)
+        pins.gpio0.into_function(),
+        // UART RX (characters received by RP2040) on pin 2 (GPIO1)
+        pins.gpio1.into_function(),
+    );
+
+    // Create new, uninitialized UART driver with one of the two UART objects
+    // from our PAC, and our UART pins. We need temporary access to the RESETS
+    // object to reset the UART.
+    let uart = hal::uart::UartPeripheral::new(p.UART0, uart_pins, &mut p.RESETS);
+
+    // Swap the uninitialised UART driver for an initialised one, passing in the
+    // desired configuration. We need to know the internal UART clock frequency
+    // to set up the baud rate dividers correctly.
+    let mut uart = uart
+        .enable(uart_config, clocks.peripheral_clock.freq())
+        .unwrap();
+
+    // ========================================================================
+    // Set up our *SPI Bus* and one *SPI Device* on the bus, and then build our
+    // *Device Driver*:
+    // ========================================================================
+
+    // Set up our SPI pins so they can be used by the *SPI Bus* driver.
+    let spi_copi = pins.gpio7.into_function::<hal::gpio::FunctionSpi>();
+    let spi_cipo = pins.gpio4.into_function::<hal::gpio::FunctionSpi>();
+    let spi_sclk = pins.gpio6.into_function::<hal::gpio::FunctionSpi>();
+
+    // Create new, uninitialized *SPI Bus* driver with one of the two *SPI*
+    // objects from our PAC, plus our data/clock pins for the *SPI Bus*.
+    //
+    // We've stubbed out most of the type parameters because the compiler can
+    // work them out for us. The only one we need to specify is the size of a
+    // word sent over the *SPI Bus* to our device - and we picked 8 bits (a
+    // byte).
+    let spi_bus = hal::spi::Spi::<_, _, _, 8>::new(p.SPI0, (spi_copi, spi_cipo, spi_sclk));
+
+    // Exchange the uninitialised *SPI Bus* driver for an initialised one, by
+    // passing in the extra bus parameters required.
+    //
+    // We need temporary access to the RESETS object to reset the SPI
+    // peripheral, and we need to know the internal clock speed in order to set
+    // up the clock dividers correctly.
+    let spi_bus = spi_bus.init(
+        &mut p.RESETS,
+        clocks.peripheral_clock.freq(),
+        16.MHz(),
+        embedded_hal::spi::MODE_0,
+    );
+
+    // The Chip Select pin. Every *SPI Device* has a unique chip select signal,
+    // and when this pin goes low, it uniquely selects our desired
+    // (hypothetical) *SPI Device* on the *SPI Bus*.
+    let spi_cs = pins.gpio8.into_push_pull_output_in_state(PinState::High);
+
+    // Create an object which represents our (hypothetical) *SPI Device* on the
+    // *SPI Bus*.
+    //
+    // We are the only task talking to this *SPI Bus*, so we can use
+    // `ExclusiveDevice` here. If we had multiple tasks accessing the same bus
+    // (e.g. you had both an accelerometer and a pressure sensor on the same
+    // bus), we would need to use a different interface to ensure that we have
+    // exclusive access to this bus (via `AtomicDevice` or
+    // `CriticalSectionDevice`, for example).
+    //
+    // See https://docs.rs/embedded-hal-bus/0.2.0/embedded_hal_bus/spi for a
+    // list of options.
+    //
+    // We can safely unwrap here, because the only possible failure is CS
+    // assertion failure and our CS pin is infallible.
+    //
+    // Note that it also takes ownership of our timer object so that it has a
+    // way of measuring elapsed time. This is required so it can handle `Delay`
+    // transactions that can put small pauses inbetween say, a `Write`
+    // transaction and a `Read` transaction (which some SPI devices require
+    // because they're a bit sluggish and take time to process things).
+    let excl_spi_dev = ExclusiveDevice::new(spi_bus, spi_cs, timer).unwrap();
+
+    // Now that we've constructed a value of type `ExclusiveDevice` (which
+    // implements the embedded-hal `SpiDevice` traits) we can finally construct
+    // our device driver.
+    let mut driver = MySpiDeviceDriver::new(excl_spi_dev);
+
+    // ========================================================================
+    // Now let's use our device driver.
+    // ========================================================================
+
+    // Let's write to the device
+    match driver.set_value(10) {
+        Ok(_) => {
+            // Do something on success
+            _ = writeln!(uart, "Wrote to device OK!");
+        }
+        Err(e) => {
+            // Do something on failure
+            _ = writeln!(uart, "Device write error: {:?}", e);
+        }
+    }
+
+    // Let's read from the device
+    match driver.get_value() {
+        Ok(value) => {
+            // Do something on success
+            _ = writeln!(uart, "Read value: {}", value);
+        }
+        Err(e) => {
+            // Do something on failure
+            _ = writeln!(uart, "Device write error: {:?}", e);
+        }
+    }
+
+    // We're done, so just sleep in an infinite loop. Your program should
+    // probably do something more useful.
+    loop {
+        cortex_m::asm::wfi();
+    }
+}
+
+// End of file