Support 0 prio tasks

ci/expected/zero-prio-task.run

@@ -0,0 +1,3 @@
+init
+hello from async
+hello from async2

examples/zero-prio-task.rs

@@ -0,0 +1,56 @@
+#![no_main]
+#![no_std]
+#![feature(type_alias_impl_trait)]
+
+use core::marker::PhantomData;
+use panic_semihosting as _;
+
+pub struct NotSend {
+    _0: PhantomData<*const ()>,
+}
+
+#[rtic::app(device = lm3s6965, peripherals = true)]
+mod app {
+    use super::NotSend;
+    use core::marker::PhantomData;
+    use cortex_m_semihosting::{debug, hprintln};
+
+    #[shared]
+    struct Shared {
+        x: NotSend,
+    }
+
+    #[local]
+    struct Local {
+        y: NotSend,
+    }
+
+    #[init]
+    fn init(_cx: init::Context) -> (Shared, Local) {
+        hprintln!("init");
+
+        async_task::spawn().unwrap();
+        async_task2::spawn().unwrap();
+
+        (
+            Shared {
+                x: NotSend { _0: PhantomData },
+            },
+            Local {
+                y: NotSend { _0: PhantomData },
+            },
+        )
+    }
+
+    #[task(priority = 0, shared = [x], local = [y])]
+    async fn async_task(_: async_task::Context) {
+        hprintln!("hello from async");
+    }
+
+    #[task(priority = 0, shared = [x])]
+    async fn async_task2(_: async_task2::Context) {
+        hprintln!("hello from async2");
+
+        debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
+    }
+}

macros/src/analyze.rs

@@ -36,6 +36,7 @@ pub fn app(analysis: analyze::Analysis, app: &App) -> Analysis {
 
     let interrupts: BTreeMap<Priority, _> = priorities
         .iter()
+        .filter(|prio| **prio > 0) // 0 prio tasks are run in main
         .copied()
         .rev()
         .map(|p| (p, available_interrupt.pop().expect("UNREACHABLE")))

macros/src/check.rs

@@ -32,6 +32,7 @@ pub fn app(app: &App) -> parse::Result<()> {
             first = Some(name);
             task.args.priority
         })
+        .filter(|prio| *prio > 0)
         .collect::<HashSet<_>>();
 
     let need = priorities.len();

macros/src/codegen/async_dispatchers.rs

@@ -26,9 +26,22 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
 
     for (&level, channel) in &analysis.channels {
         let mut stmts = vec![];
+
+        let dispatcher_name = if level > 0 {
+            util::suffixed(&interrupts.get(&level).expect("UNREACHABLE").0.to_string())
+        } else {
+            util::zero_prio_dispatcher_ident()
+        };
+
+        let pend_interrupt = if level > 0 {
             let device = &app.args.device;
             let enum_ = util::interrupt_ident();
-        let interrupt = util::suffixed(&interrupts[&level].0.to_string());
+
+            quote!(rtic::pend(#device::#enum_::#dispatcher_name);)
+        } else {
+            // For 0 priority tasks we don't need to pend anything
+            quote!()
+        };
 
         for name in channel.tasks.iter() {
             let exec_name = util::internal_task_ident(name, "EXEC");
@@ -60,27 +73,28 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
                     #executor_run_ident.store(false, core::sync::atomic::Ordering::Relaxed);
                     if (&mut *#exec_name.get_mut()).poll(||  {
                         #executor_run_ident.store(true, core::sync::atomic::Ordering::Release);
-                        rtic::pend(#device::#enum_::#interrupt);
+                        #pend_interrupt
                     }) && #rq.load(core::sync::atomic::Ordering::Relaxed) {
                         // If the ready queue is not empty and the executor finished, restart this
                         // dispatch to check if the executor should be restarted.
-                        rtic::pend(#device::#enum_::#interrupt);
+                        #pend_interrupt
                     }
                 }
             ));
         }
 
+        if level > 0 {
             let doc = format!(
                 "Interrupt handler to dispatch async tasks at priority {}",
                 level
             );
-        let attribute = &interrupts[&level].1.attrs;
+            let attribute = &interrupts.get(&level).expect("UNREACHABLE").1.attrs;
             items.push(quote!(
                 #[allow(non_snake_case)]
                 #[doc = #doc]
                 #[no_mangle]
                 #(#attribute)*
-            unsafe fn #interrupt() {
+                unsafe fn #dispatcher_name() {
                     /// The priority of this interrupt handler
                     const PRIORITY: u8 = #level;
 
@@ -94,6 +108,21 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
                     });
                 }
             ));
+        } else {
+            items.push(quote!(
+                #[allow(non_snake_case)]
+                unsafe fn #dispatcher_name() -> ! {
+                    loop {
+                        // Have the acquire/release semantics outside the checks to no overdo it
+                        core::sync::atomic::fence(core::sync::atomic::Ordering::Acquire);
+
+                        #(#stmts)*
+
+                        core::sync::atomic::fence(core::sync::atomic::Ordering::Release);
+                    }
+                }
+            ));
+        }
     }
 
     quote!(#(#items)*)

macros/src/codegen/main.rs

@@ -16,11 +16,14 @@ pub fn codegen(app: &App, analysis: &Analysis) -> TokenStream2 {
         let name = &idle.name;
         quote!(#name(#name::Context::new()))
     } else {
-        // TODO: No idle defined, check for 0-priority tasks and generate an executor if needed
-
+        if analysis.channels.get(&0).is_some() {
+            let dispatcher = util::zero_prio_dispatcher_ident();
+            quote!(#dispatcher();)
+        } else {
             quote!(loop {
                 rtic::export::nop()
             })
+        }
     };
 
     let main = util::suffixed("main");

macros/src/codegen/module.rs

@@ -135,13 +135,14 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
         // Store a copy of the task cfgs
         task_cfgs = cfgs.clone();
 
+        let pend_interrupt = if priority > 0 {
             let device = &app.args.device;
             let enum_ = util::interrupt_ident();
-        let interrupt = &analysis
-            .interrupts
-            .get(&priority)
-            .expect("RTIC-ICE: interrupt identifier not found")
-            .0;
+            let interrupt = &analysis.interrupts.get(&priority).expect("UREACHABLE").0;
+            quote!(rtic::pend(#device::#enum_::#interrupt);)
+        } else {
+            quote!()
+        };
 
         let internal_spawn_ident = util::internal_task_ident(name, "spawn");
 
@@ -160,7 +161,7 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
                     Err(())
                 } else {
                     #rq.store(true, core::sync::atomic::Ordering::Release);
-                    rtic::pend(#device::#enum_::#interrupt);
+                    #pend_interrupt
                     Ok(())
                 }
             }

macros/src/codegen/util.rs

@@ -187,6 +187,10 @@ pub fn need_to_lock_ident(name: &Ident) -> Ident {
     Ident::new(&format!("{}_that_needs_to_be_locked", name), name.span())
 }
 
+pub fn zero_prio_dispatcher_ident() -> Ident {
+    Ident::new("__rtic_internal_async_0_prio_dispatcher", Span::call_site())
+}
+
 /// The name to get better RT flag errors
 pub fn rt_err_ident() -> Ident {
     Ident::new(

macros/src/syntax/analyze.rs

@@ -248,35 +248,36 @@ pub(crate) fn app(app: &App) -> Result<Analysis, syn::Error> {
         }
     }
 
-    // Most shared resources need to be `Send`
+    // Most shared resources need to be `Send`, only 0 prio does not need it
     let mut send_types = SendTypes::new();
-    let owned_by_idle = Ownership::Owned { priority: 0 };
+
     for (name, res) in app.shared_resources.iter() {
-        // Handle not owned by idle
         if ownerships
             .get(name)
-            .map(|ownership| *ownership != owned_by_idle)
+            .map(|ownership| match *ownership {
+                Ownership::Owned { priority: ceiling }
+                | Ownership::CoOwned { priority: ceiling }
+                | Ownership::Contended { ceiling } => ceiling != 0,
+            })
             .unwrap_or(false)
         {
             send_types.insert(res.ty.clone());
         }
     }
 
-    // Most local resources need to be `Send` as well
+    // Most local resources need to be `Send` as well, only 0 prio does not need it
     for (name, res) in app.local_resources.iter() {
-        if let Some(idle) = &app.idle {
-            // Only Send if not in idle or not at idle prio
-            if idle.args.local_resources.get(name).is_none()
-                && !ownerships
+        if ownerships
             .get(name)
-                    .map(|ownership| *ownership != owned_by_idle)
+            .map(|ownership| match *ownership {
+                Ownership::Owned { priority: ceiling }
+                | Ownership::CoOwned { priority: ceiling }
+                | Ownership::Contended { ceiling } => ceiling != 0,
+            })
             .unwrap_or(false)
         {
             send_types.insert(res.ty.clone());
         }
-        } else {
-            send_types.insert(res.ty.clone());
-        }
     }
 
     let mut channels = Channels::new();