add example to rp: orchestrate multiple tasks

examples/rp/src/bin/orchestrate_tasks.rs

@@ -0,0 +1,267 @@
+//! This example demonstrates some approaches to communicate between tasks in order to orchestrate the state of the system.
+//!
+//! We demonstrate how to:
+//! - use a channel to send messages between tasks, in this case here in order to have one task control the state of the system.
+//! - use a signal to terminate a task.
+//! - use command channels to send commands to another task.
+//! - use different ways to receive messages, from a straightforwar awaiting on one channel to a more complex awaiting on multiple channels.
+//!
+//! There are more patterns to orchestrate tasks, this is just one example.
+//!
+//! We will use these tasks to generate example "state information":
+//! - a task that generates random numbers in intervals of 60s
+//! - a task that generates random numbers in intervals of 30s
+//! - a task that generates random numbers in intervals of 90s
+//! - a task that notifies about being attached/disattached from usb power
+//! - a task that measures vsys voltage in intervals of 30s
+
+#![no_std]
+#![no_main]
+
+use assign_resources::assign_resources;
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_futures::select::{select, Either};
+use embassy_rp::adc::{Adc, Channel, Config, InterruptHandler};
+use embassy_rp::bind_interrupts;
+use embassy_rp::clocks::RoscRng;
+use embassy_rp::gpio::{Input, Pull};
+use embassy_rp::peripherals;
+use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
+use embassy_sync::{channel, signal};
+use embassy_time::{Duration, Timer};
+use rand::RngCore;
+use {defmt_rtt as _, panic_probe as _};
+
+// This is just some preparation, see example `assign_resources.rs` for more information on this. We prep the rresources that we will be using in different tasks.
+// **Note**: This will not work with a board that has a wifi chip, because the wifi chip uses pins 24 and 29 for its own purposes. A way around this in software
+// is not trivial, at least if you intend to use wifi, too. Workaround is to wire from vsys and vbus pins to appropriate pins on the board through a voltage divider. Then use those pins.
+// For this example it will not matter much, the concept of what we are showing remains valid.
+assign_resources! {
+    vsys: Vsys {
+        adc: ADC,
+        pin_29: PIN_29,
+    },
+    vbus: Vbus {
+        pin_24: PIN_24,
+    },
+}
+
+bind_interrupts!(struct Irqs {
+    ADC_IRQ_FIFO => InterruptHandler;
+});
+
+/// This is the type of Events that we will send from the worker tasks to the orchestrating task.
+enum Events {
+    UsbPowered(bool),
+    VsysVoltage(f32),
+    FirstRandomSeed(u32),
+    SecondRandomSeed(u32),
+    ThirdRandomSeed(u32),
+}
+
+/// This is the type of Commands that we will send from the orchestrating task to the worker tasks.
+/// Note that we are lazy here and only have one command, you might want to have more.
+enum Commands {
+    /// This command will stop the appropriate worker task
+    Stop,
+}
+
+/// This is the state of the system, we will use this to orchestrate the system. This is a simple example, in a real world application this would be more complex.
+#[derive(Default, Debug, Clone, Format)]
+struct State {
+    usb_powered: bool,
+    vsys_voltage: f32,
+    first_random_seed: u32,
+    second_random_seed: u32,
+    third_random_seed: u32,
+    times_we_got_first_random_seed: u8,
+    maximum_times_we_want_first_random_seed: u8,
+}
+
+impl State {
+    fn new() -> Self {
+        Self {
+            usb_powered: false,
+            vsys_voltage: 0.0,
+            first_random_seed: 0,
+            second_random_seed: 0,
+            third_random_seed: 0,
+            times_we_got_first_random_seed: 0,
+            maximum_times_we_want_first_random_seed: 3,
+        }
+    }
+}
+
+/// Channel for the events that we want the orchestrator to react to, all state events are of the type Enum Events.
+/// We use a channel with an arbitrary size of 10, the precise size of the queue depends on your use case. This depends on how many events we
+/// expect to be generated in a given time frame and how fast the orchestrator can react to them. And then if we rather want the senders to wait for
+/// new slots in the queue or if we want the orchestrator to have a backlog of events to process. In this case here we expect to always be enough slots
+/// in the queue, so the worker tasks can in all nominal cases send their events and continue with their work without waiting.
+/// For the events we - in this case here -  do not want to loose any events, so a channel is a good choice. See embassy_sync docs for other options.
+static EVENT_CHANNEL: channel::Channel<CriticalSectionRawMutex, Events, 10> = channel::Channel::new();
+
+/// Signal for stopping the first random signal task. We use a signal here, because we need no queue. It is suffiient to have one signal active.
+static STOP_FIRST_RANDOM_SIGNAL: signal::Signal<CriticalSectionRawMutex, Commands> = signal::Signal::new();
+
+// And now we can put all this into use
+
+/// This is the main task, that will not do very much besides spawning the other tasks. This is a design choice, you could do the
+/// orchestrating here. This is to show that we do not need a main loop here, the system will run indefinitely as long as at least one task is running.
+#[embassy_executor::main]
+async fn main(spawner: Spawner) {
+    // initialize the peripherals
+    let p = embassy_rp::init(Default::default());
+    // split the resources, for convenience - see above
+    let r = split_resources! {p};
+
+    // spawn the tasks
+    spawner.spawn(orchestrate(spawner)).unwrap();
+    spawner.spawn(random_30s(spawner)).unwrap();
+    spawner.spawn(random_60s(spawner)).unwrap();
+    spawner.spawn(random_90s(spawner)).unwrap();
+    spawner.spawn(usb_power(spawner, r.vbus)).unwrap();
+    spawner.spawn(vsys_voltage(spawner, r.vsys)).unwrap();
+}
+
+/// This is the task handling the system state and orchestrating the other tasks. WEe can regard this as the "main loop" of the system.
+#[embassy_executor::task]
+async fn orchestrate(_spawner: Spawner) {
+    let mut state = State::new();
+
+    // we need to have a receiver for the events
+    let receiver = EVENT_CHANNEL.receiver();
+
+    loop {
+        // we await on the receiver, this will block until a new event is available
+        // as an alternative to this, we could also await on multiple channels, this would block until at least one of the channels has an event
+        // see the embassy_futures docs: https://docs.embassy.dev/embassy-futures/git/default/select/index.html
+        // The task random_30s does a select, if you want to have a look at that.
+        // Another reason to use select may also be that we want to have a timeout, so we can react to the absence of events within a time frame.
+        // We keep it simple here.
+        let event = receiver.receive().await;
+
+        // react to the events
+        match event {
+            Events::UsbPowered(usb_powered) => {
+                // update the state and/or react to the event here
+                state.usb_powered = usb_powered;
+                info!("Usb powered: {}", usb_powered);
+            }
+            Events::VsysVoltage(voltage) => {
+                // update the state and/or react to the event here
+                state.vsys_voltage = voltage;
+                info!("Vsys voltage: {}", voltage);
+            }
+            Events::FirstRandomSeed(seed) => {
+                // update the state and/or react to the event here
+                state.first_random_seed = seed;
+                // here we change some meta state, we count how many times we got the first random seed
+                state.times_we_got_first_random_seed += 1;
+                info!(
+                    "First random seed: {}, and that was iteration {} of receiving this.",
+                    seed, &state.times_we_got_first_random_seed
+                );
+            }
+            Events::SecondRandomSeed(seed) => {
+                // update the state and/or react to the event here
+                state.second_random_seed = seed;
+                info!("Second random seed: {}", seed);
+            }
+            Events::ThirdRandomSeed(seed) => {
+                // update the state and/or react to the event here
+                state.third_random_seed = seed;
+                info!("Third random seed: {}", seed);
+            }
+        }
+        // we now have an altered state
+        // there is a crate for detecting field changes on crates.io (https://crates.io/crates/fieldset) that might be useful here
+        // for now we just keep it simple
+        info!("State: {:?}", &state);
+
+        // here we react to the state, in this case here we want to stop the first random seed task after we got it a defined number of times
+        if state.times_we_got_first_random_seed == state.maximum_times_we_want_first_random_seed {
+            info!("Stopping the first random signal task");
+            // we send a command to the task
+            STOP_FIRST_RANDOM_SIGNAL.signal(Commands::Stop);
+        }
+    }
+}
+
+/// This task will generate random numbers in intervals of 30s
+/// The task will terminate after it has received a command signal to stop, see the orchestrate task for that.
+#[embassy_executor::task]
+async fn random_30s(_spawner: Spawner) {
+    let mut rng = RoscRng;
+    let sender = EVENT_CHANNEL.sender();
+    loop {
+        // we either await on the timer or the signal, whichever comes first.
+        let futures = select(Timer::after(Duration::from_secs(30)), STOP_FIRST_RANDOM_SIGNAL.wait()).await;
+        match futures {
+            Either::First(_) => {
+                // we received are operating on the timer
+                info!("30s are up, generating random number");
+                let random_number = rng.next_u32();
+                sender.send(Events::FirstRandomSeed(random_number)).await;
+            }
+            Either::Second(_) => {
+                // we received the signal to stop
+                info!("Received signal to stop, goodbye!");
+                break;
+            }
+        }
+    }
+}
+
+/// This task will generate random numbers in intervals of 60s
+#[embassy_executor::task]
+async fn random_60s(_spawner: Spawner) {
+    let mut rng = RoscRng;
+    let sender = EVENT_CHANNEL.sender();
+    loop {
+        Timer::after(Duration::from_secs(60)).await;
+        let random_number = rng.next_u32();
+        sender.send(Events::SecondRandomSeed(random_number)).await;
+    }
+}
+
+/// This task will generate random numbers in intervals of 90s
+#[embassy_executor::task]
+async fn random_90s(_spawner: Spawner) {
+    let mut rng = RoscRng;
+    let sender = EVENT_CHANNEL.sender();
+    loop {
+        Timer::after(Duration::from_secs(90)).await;
+        let random_number = rng.next_u32();
+        sender.send(Events::ThirdRandomSeed(random_number)).await;
+    }
+}
+
+/// This task will notify if we are connected to usb power
+#[embassy_executor::task]
+pub async fn usb_power(_spawner: Spawner, r: Vbus) {
+    let mut vbus_in = Input::new(r.pin_24, Pull::None);
+    let sender = EVENT_CHANNEL.sender();
+    loop {
+        sender.send(Events::UsbPowered(vbus_in.is_high())).await;
+        vbus_in.wait_for_any_edge().await;
+    }
+}
+
+/// This task will measure the vsys voltage in intervals of 30s
+#[embassy_executor::task]
+pub async fn vsys_voltage(_spawner: Spawner, r: Vsys) {
+    let mut adc = Adc::new(r.adc, Irqs, Config::default());
+    let vsys_in = r.pin_29;
+    let mut channel = Channel::new_pin(vsys_in, Pull::None);
+    let sender = EVENT_CHANNEL.sender();
+    loop {
+        // read the adc value
+        let adc_value = adc.read(&mut channel).await.unwrap();
+        // convert the adc value to voltage.
+        // 3.3 is the reference voltage, 3.0 is the factor for the inbuilt voltage divider and 4096 is the resolution of the adc
+        let voltage = (adc_value as f32) * 3.3 * 3.0 / 4096.0;
+        sender.send(Events::VsysVoltage(voltage)).await;
+        Timer::after(Duration::from_secs(30)).await;
+    }
+}