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critical_section.rs
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critical_section.rs
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use core::cell::RefCell;
use critical_section::Mutex;
use embedded_hal::delay::DelayNs;
use embedded_hal::digital::OutputPin;
use embedded_hal::spi::{ErrorType, Operation, SpiBus, SpiDevice};
use super::DeviceError;
use crate::spi::shared::transaction;
/// `critical-section`-based shared bus [`SpiDevice`] implementation.
///
/// This allows for sharing an [`SpiBus`], obtaining multiple [`SpiDevice`] instances,
/// each with its own `CS` pin.
///
/// Sharing is implemented with a `critical-section` [`Mutex`]. A critical section is taken for
/// the entire duration of a transaction. This allows sharing a single bus across multiple threads (interrupt priority levels).
/// The downside is critical sections typically require globally disabling interrupts, so `CriticalSectionDevice` will likely
/// negatively impact real-time properties, such as interrupt latency. If you can, prefer using
/// [`RefCellDevice`](super::RefCellDevice) instead, which does not require taking critical sections.
pub struct CriticalSectionDevice<'a, BUS, CS, D> {
bus: &'a Mutex<RefCell<BUS>>,
cs: CS,
delay: D,
}
impl<'a, BUS, CS, D> CriticalSectionDevice<'a, BUS, CS, D> {
/// Create a new [`CriticalSectionDevice`].
///
/// This sets the `cs` pin high, and returns an error if that fails. It is recommended
/// to set the pin high the moment it's configured as an output, to avoid glitches.
#[inline]
pub fn new(bus: &'a Mutex<RefCell<BUS>>, mut cs: CS, delay: D) -> Result<Self, CS::Error>
where
CS: OutputPin,
{
cs.set_high()?;
Ok(Self { bus, cs, delay })
}
}
impl<'a, BUS, CS> CriticalSectionDevice<'a, BUS, CS, super::NoDelay> {
/// Create a new [`CriticalSectionDevice`] without support for in-transaction delays.
///
/// This sets the `cs` pin high, and returns an error if that fails. It is recommended
/// to set the pin high the moment it's configured as an output, to avoid glitches.
///
/// **Warning**: The returned instance *technically* doesn't comply with the `SpiDevice`
/// contract, which mandates delay support. It is relatively rare for drivers to use
/// in-transaction delays, so you might still want to use this method because it's more practical.
///
/// Note that a future version of the driver might start using delays, causing your
/// code to panic. This wouldn't be considered a breaking change from the driver side, because
/// drivers are allowed to assume `SpiDevice` implementations comply with the contract.
/// If you feel this risk outweighs the convenience of having `cargo` automatically upgrade
/// the driver crate, you might want to pin the driver's version.
///
/// # Panics
///
/// The returned device will panic if you try to execute a transaction
/// that contains any operations of type [`Operation::DelayNs`].
#[inline]
pub fn new_no_delay(bus: &'a Mutex<RefCell<BUS>>, mut cs: CS) -> Result<Self, CS::Error>
where
CS: OutputPin,
{
cs.set_high()?;
Ok(Self {
bus,
cs,
delay: super::NoDelay,
})
}
}
impl<'a, BUS, CS, D> ErrorType for CriticalSectionDevice<'a, BUS, CS, D>
where
BUS: ErrorType,
CS: OutputPin,
{
type Error = DeviceError<BUS::Error, CS::Error>;
}
impl<'a, Word: Copy + 'static, BUS, CS, D> SpiDevice<Word> for CriticalSectionDevice<'a, BUS, CS, D>
where
BUS: SpiBus<Word>,
CS: OutputPin,
D: DelayNs,
{
#[inline]
fn transaction(&mut self, operations: &mut [Operation<'_, Word>]) -> Result<(), Self::Error> {
critical_section::with(|cs| {
let bus = &mut *self.bus.borrow_ref_mut(cs);
transaction(operations, bus, &mut self.delay, &mut self.cs)
})
}
}