Merge #88

88: make compilable on stable r=japaric a=japaric

This PR makes this crate compilable on stable when the "inline-asm" and "singleton" Cargo features
are disabled (they are enabled by default to maintain backwards compatibility).

The main change has been replacing almost (\*) all inline `asm!` invocations with FFI calls into
external assembly files.

(\*) Stuff that has not been converted into external assembly file and thus is not available on
stable:

- Reading the (A)PSR register (I'm not sure if this will work with the extra function call overhead)

- Reading and writing the Link Register (LR)

- Reading and writing the Program Counter (PC)

I would appreciate if someone checked that all the stuff that's now using FFI calls has the same
semantics as the inline `asm!` version.


Co-authored-by: Jorge Aparicio <jorge@japaric.io>

1 files changed, 9 insertions, 13 deletions

diff --git a/src/macros.rs b/src/macros.rs
index 7d2cf6a..e41cdc5 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -53,33 +53,29 @@ macro_rules! iprintln {
 macro_rules! singleton {
     (: $ty:ty = $expr:expr) => {
         $crate::interrupt::free(|_| {
-            static mut USED: bool = false;
-            static mut VAR: $crate::UntaggedOption<$ty> = $crate::UntaggedOption { none: () };
-
+            static mut VAR: Option<$ty> = None;
 
             #[allow(unsafe_code)]
-            let used = unsafe { USED };
+            let used = unsafe { VAR.is_some() };
             if used {
                 None
             } else {
-                #[allow(unsafe_code)]
-                unsafe { USED = true }
-
                 let expr = $expr;
 
                 #[allow(unsafe_code)]
-                unsafe { VAR.some = expr }
+                unsafe {
+                    VAR = Some(expr)
+                }
 
                 #[allow(unsafe_code)]
-                let var: &'static mut _ = unsafe { &mut VAR.some };
-
-                Some(var)
+                unsafe {
+                    VAR.as_mut()
+                }
             }
         })
-    }
+    };
 }
 
-
 /// ``` compile_fail
 /// #[macro_use(singleton)]
 /// extern crate cortex_m;