Add example for sharing things between tasks

1 files changed, 140 insertions, 0 deletions

diff --git a/examples/rp/src/bin/sharing.rs b/examples/rp/src/bin/sharing.rs
new file mode 100644
index 000000000..0761500ef
--- /dev/null
+++ b/examples/rp/src/bin/sharing.rs
@@ -0,0 +1,140 @@
+//! This example shows some common strategies for sharing resources between tasks.
+
+#![no_std]
+#![no_main]
+
+use core::cell::{Cell, RefCell};
+use core::sync::atomic::{AtomicU32, Ordering};
+
+use cortex_m_rt::entry;
+use defmt::info;
+use embassy_executor::{Executor, InterruptExecutor};
+use embassy_rp::clocks::RoscRng;
+use embassy_rp::interrupt::{InterruptExt, Priority};
+use embassy_rp::peripherals::UART0;
+use embassy_rp::uart::{self, InterruptHandler, UartTx};
+use embassy_rp::{bind_interrupts, interrupt};
+use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
+use embassy_sync::{blocking_mutex, mutex};
+use embassy_time::{Duration, Ticker};
+use rand::RngCore;
+use static_cell::{ConstStaticCell, StaticCell};
+use {defmt_rtt as _, panic_probe as _};
+
+type UartMutex = mutex::Mutex<CriticalSectionRawMutex, UartTx<'static, UART0, uart::Async>>;
+
+struct MyType {
+    inner: u32,
+}
+
+static EXECUTOR_HI: InterruptExecutor = InterruptExecutor::new();
+static EXECUTOR_LOW: StaticCell<Executor> = StaticCell::new();
+
+// Use Atomics for simple values
+static ATOMIC: AtomicU32 = AtomicU32::new(0);
+
+// Use blocking Mutex with Cell/RefCell for sharing non-async things
+static MUTEX_BLOCKING: blocking_mutex::Mutex<CriticalSectionRawMutex, RefCell<MyType>> =
+    blocking_mutex::Mutex::new(RefCell::new(MyType { inner: 0 }));
+
+bind_interrupts!(struct Irqs {
+    UART0_IRQ => InterruptHandler<UART0>;
+});
+
+#[interrupt]
+unsafe fn SWI_IRQ_0() {
+    EXECUTOR_HI.on_interrupt()
+}
+
+#[entry]
+fn main() -> ! {
+    let p = embassy_rp::init(Default::default());
+    info!("Here we go!");
+
+    let uart = UartTx::new(p.UART0, p.PIN_0, p.DMA_CH0, uart::Config::default());
+    // Use the async Mutex for sharing async things (built-in interior mutability)
+    static UART: StaticCell<UartMutex> = StaticCell::new();
+    let uart = UART.init(mutex::Mutex::new(uart));
+
+    // High-priority executor: runs in interrupt mode
+    interrupt::SWI_IRQ_0.set_priority(Priority::P3);
+    let spawner = EXECUTOR_HI.start(interrupt::SWI_IRQ_0);
+    spawner.must_spawn(task_a(uart));
+
+    // Low priority executor: runs in thread mode
+    let executor = EXECUTOR_LOW.init(Executor::new());
+    executor.run(|spawner| {
+        // No Mutex needed when sharing between tasks running on the same executor
+
+        // Use Cell for Copy-types
+        static CELL: ConstStaticCell<Cell<[u8; 4]>> = ConstStaticCell::new(Cell::new([0; 4]));
+        let cell = CELL.take();
+
+        // Use RefCell for &mut access
+        static REF_CELL: ConstStaticCell<RefCell<MyType>> = ConstStaticCell::new(RefCell::new(MyType { inner: 0 }));
+        let ref_cell = REF_CELL.take();
+
+        spawner.must_spawn(task_b(uart, cell, ref_cell));
+        spawner.must_spawn(task_c(cell, ref_cell));
+    });
+}
+
+#[embassy_executor::task]
+async fn task_a(uart: &'static UartMutex) {
+    let mut ticker = Ticker::every(Duration::from_secs(1));
+    loop {
+        let random = RoscRng.next_u32();
+
+        {
+            let mut uart = uart.lock().await;
+            uart.write(b"task a").await.unwrap();
+            // The uart lock is released when it goes out of scope
+        }
+
+        ATOMIC.store(random, Ordering::Relaxed);
+
+        MUTEX_BLOCKING.lock(|x| x.borrow_mut().inner = random);
+
+        ticker.next().await;
+    }
+}
+
+#[embassy_executor::task]
+async fn task_b(uart: &'static UartMutex, cell: &'static Cell<[u8; 4]>, ref_cell: &'static RefCell<MyType>) {
+    let mut ticker = Ticker::every(Duration::from_secs(1));
+    loop {
+        let random = RoscRng.next_u32();
+
+        uart.lock().await.write(b"task b").await.unwrap();
+
+        cell.set(random.to_be_bytes());
+
+        ref_cell.borrow_mut().inner = random;
+
+        ticker.next().await;
+    }
+}
+
+#[embassy_executor::task]
+async fn task_c(cell: &'static Cell<[u8; 4]>, ref_cell: &'static RefCell<MyType>) {
+    let mut ticker = Ticker::every(Duration::from_secs(1));
+    loop {
+        info!("=======================");
+
+        let atomic = ATOMIC.load(Ordering::Relaxed);
+        info!("atomic: {}", atomic);
+
+        MUTEX_BLOCKING.lock(|x| {
+            let val = x.borrow().inner;
+            info!("blocking mutex: {}", val);
+        });
+
+        let cell_val = cell.get();
+        info!("cell: {:?}", cell_val);
+
+        let ref_cell_val = ref_cell.borrow().inner;
+        info!("ref_cell: {:?}", ref_cell_val);
+
+        ticker.next().await;
+    }
+}