Why .start_app_core does not run in this case?

[trinhanhtuan]

Hello,
I have the following code, I don't understand why if I remove the loop {..} in main function then the closure in .start_app_core is not initiated and executed, only the mspawner.spawn(enable_disable_led(led_ctrl_signal)).ok(); runs.
Can someone explain? Thank you.

#[embassy_executor::task]
async fn control_led(
    mut led: Output<'static>,
    ctrl: &'static Signal<CriticalSectionRawMutex, bool>)
{
 /* code to turn on/off the led */
}

#[embassy_executor::task]
async fn enable_disable_led(
    lcs: &'static Signal<CriticalSectionRawMutex, bool>)
{
 /* code to send signal to turn on/off the led */
}

#[main]
async fn main(mspawner: Spawner) {
 ...
 let _guard = cpu_control.start_app_core(
    unsafe { &mut *addr_of_mut!(APP_CORE_STACK) },
    move || {                    // will not run if the bottom loop is removed
        static EXECUTOR: StaticCell<Executor> = StaticCell::new();
        let executor = EXECUTOR.init(Executor::new());
        info!("APP_CORE spawning done!");
        executor.run(
            |spawner| {  spawner.spawn(control_led(led, led_ctrl_signal)).ok();  }
        );
    }).unwrap();

 mspawner.spawn(enable_disable_led(led_ctrl_signal)).ok();

 let mut ticker = Ticker::every(Duration::from_secs(2));
 loop {
   ticker.next().await;
 }
}

[bjoernQ]

When the _guard is dropped it will stop the second core. Having the loop will keep it alive while when removing it, main will finish and the _guard gets out of scope and gets dropped

See https://docs.esp-rs.org/esp-hal/esp-hal/0.22.0/esp32s3/esp_hal/cpu_control/struct.CpuControl.html#method.start_app_core

Dropping the returned guard will park the core.

[trinhanhtuan]

Thank you but if the _gaurd is droped when main goes out of scope (i.e. terminate the program?) then why the enable_disable_led(led_ctrl_signal) still run? Thanks.

[bjoernQ]

it's spawned via mspawner which is the spawner for the executor on core 0 - core 0 will keep running. The guard only controls core 1

[trinhanhtuan]

Yes, it is much clearer after I use cargo expand to see what eactly the main looks like. Thank you.