Merge #562

562: Replace default WFI with simpler NOP r=korken89 a=AfoHT

As noted by #561 there are multiple issues with various hardware implementations and debugging together with sleep modes.

As RTIC strives to be a generic framework (even though this is an implementation targeting cortex-m) the decision having `WFI` as the default `idle` task causes issues in some hardware, raising the barrier to entry.

This changes the default behaviour to do a simple `NOP` instead, adding documentation how to provide a custom `idle` task achieving the old default behaviour. Also removes the automatic setting of SLEEPONEXIT bit when no `idle` was provided, delegating this to the user.

This was discussed on the weekly meeting 2021-12-14 and this was the favoured solution.

Fixes #561 

Co-authored-by: Henrik Tjäder <henrik@grepit.se>

2 files changed, 1 insertions, 8 deletions

diff --git a/macros/src/codegen/idle.rs b/macros/src/codegen/idle.rs
index d6539316..0dededa4 100644
--- a/macros/src/codegen/idle.rs
+++ b/macros/src/codegen/idle.rs
@@ -85,7 +85,7 @@ pub fn codegen(
             vec![],
             None,
             quote!(loop {
-                rtic::export::wfi()
+                rtic::export::nop()
             }),
         )
     }
diff --git a/macros/src/codegen/pre_init.rs b/macros/src/codegen/pre_init.rs
index 42cc0552..7aaf20fc 100644
--- a/macros/src/codegen/pre_init.rs
+++ b/macros/src/codegen/pre_init.rs
@@ -122,12 +122,5 @@ pub fn codegen(app: &App, analysis: &Analysis, extra: &Extra) -> Vec<TokenStream
             ));
         }
     }
-
-    // If there's no user `#[idle]` then optimize returning from interrupt handlers
-    if app.idle.is_none() {
-        // Set SLEEPONEXIT bit to enter sleep mode when returning from ISR
-        stmts.push(quote!(core.SCB.scr.modify(|r| r | 1 << 1);));
-    }
-
     stmts
 }