Using async softare tasks.

There have been a few changes to software tasks. They are outlined below.

Software tasks must now be async.

All software tasks are now required to be async.

Required changes.

All of the tasks in your project that do not bind to an interrupt must now be an async fn. For example:

#[task(
    local = [ some_resource ],
    shared = [ my_shared_resource ],
    priority = 2
)]
fn my_task(cx: my_task::Context) {
    cx.local.some_resource.do_trick();
    cx.shared.my_shared_resource.lock(|s| s.do_shared_thing());
}

becomes

#[task(
    local = [ some_resource ],
    shared = [ my_shared_resource ],
    priority = 2
)]
async fn my_task(cx: my_task::Context) {
    cx.local.some_resource.do_trick();
    cx.shared.my_shared_resource.lock(|s| s.do_shared_thing());
}

Software tasks may now run forever

The new async software tasks are allowed to run forever, on one precondition: there must be an await within the infinite loop of the task. An example of such a task:

#[task(local = [ my_channel ] )]
async fn my_task_that_runs_forever(cx: my_task_that_runs_forever::Context) {
    loop {
        let value = cx.local.my_channel.recv().await;
        do_something_with_value(value);
    }
}

spawn_after and spawn_at have been removed.

As discussed in the Migrating to rtic-monotonics chapter, spawn_after and spawn_at are no longer available.