Merge #1054

1054: riscv fixes r=lulf a=swolix

With these changes I can run embassy on our RISC-V processor, please consider merging this, feedback is very welcome.

I don't fully understand the code in the executor, but I have implemented a critical section by globally disabling interrupts, which means the wfi inside the critical section will hang the whole thing.

Co-authored-by: Sijmen Woutersen <sijmen.woutersen@gmail.com>

embassy-executor/Cargo.toml

@@ -31,6 +31,7 @@ flavors = [
 default = []
 std = ["embassy-macros/std", "critical-section/std"]
 wasm = ["dep:wasm-bindgen", "dep:js-sys", "embassy-macros/wasm"]
+riscv = ["embassy-macros/riscv"]
 
 # Enable nightly-only features
 nightly = []

embassy-executor/src/arch/riscv32.rs

@@ -56,18 +56,10 @@ impl Executor {
                 self.inner.poll();
                 // we do not care about race conditions between the load and store operations, interrupts
                 // will only set this value to true.
-                critical_section::with(|_| {
                 // if there is work to do, loop back to polling
-                    // TODO can we relax this?
-                    if SIGNAL_WORK_THREAD_MODE.load(Ordering::SeqCst) {
-                        SIGNAL_WORK_THREAD_MODE.store(false, Ordering::SeqCst);
-                    }
-                    // if not, wait for interrupt
-                    else {
+                if !SIGNAL_WORK_THREAD_MODE.fetch_and(false, Ordering::SeqCst) {
                     core::arch::asm!("wfi");
                 }
-                });
-                // if an interrupt occurred while waiting, it will be serviced here
             }
         }
     }

embassy-macros/Cargo.toml

@@ -23,6 +23,7 @@ proc-macro = true
 [features]
 std = []
 wasm = []
+riscv = []
 
 # Enabling this cause interrupt::take! to require embassy-executor
 rtos-trace-interrupt = []

embassy-macros/src/macros/main.rs

@@ -45,7 +45,7 @@ pub fn run(args: syn::AttributeArgs, f: syn::ItemFn) -> Result<TokenStream, Toke
         }
     };
 
-    #[cfg(all(feature = "std", not(feature = "wasm")))]
+    #[cfg(all(feature = "std", not(feature = "wasm"), not(feature = "riscv")))]
     let main = quote! {
         fn main() -> ! {
             let mut executor = ::embassy_executor::Executor::new();
@@ -57,13 +57,24 @@ pub fn run(args: syn::AttributeArgs, f: syn::ItemFn) -> Result<TokenStream, Toke
         }
     };
 
-    #[cfg(all(not(feature = "std"), not(feature = "wasm")))]
+    #[cfg(all(not(feature = "std"), not(feature = "wasm"), not(feature = "riscv")))]
     let main = quote! {
         #[cortex_m_rt::entry]
         fn main() -> ! {
             let mut executor = ::embassy_executor::Executor::new();
             let executor = unsafe { __make_static(&mut executor) };
+            executor.run(|spawner| {
+                spawner.must_spawn(__embassy_main(spawner));
+            })
+        }
+    };
 
+    #[cfg(all(not(feature = "std"), not(feature = "wasm"), feature = "riscv"))]
+    let main = quote! {
+        #[riscv_rt::entry]
+        fn main() -> ! {
+            let mut executor = ::embassy_executor::Executor::new();
+            let executor = unsafe { __make_static(&mut executor) };
             executor.run(|spawner| {
                 spawner.must_spawn(__embassy_main(spawner));
             })