Add barriers after FPU enabling

Author: thalesfragoso

cortex-m-rt/Cargo.toml

@@ -19,9 +19,9 @@ links = "cortex-m-rt" # Prevent multiple versions of cortex-m-rt being linked
 [dependencies]
 r0 = "1.0"
 cortex-m-rt-macros = { path = "macros", version = "=0.6.11" }
+cortex-m = "0.6"
 
 [dev-dependencies]
-cortex-m = "0.6"
 panic-halt = "0.2.0"
 cortex-m-semihosting = "0.3"
 

cortex-m-rt/src/lib.rs

@@ -916,12 +916,12 @@ pub unsafe extern "C" fn Reset() -> ! {
     r0::zero_bss(&mut __sbss, &mut __ebss);
     r0::init_data(&mut __sdata, &mut __edata, &__sidata);
 
+    #[allow(clippy::match_single_binding)]
     match () {
         #[cfg(not(has_fpu))]
         () => main(),
         #[cfg(has_fpu)]
         () => {
-            // We redefine these here to avoid pulling the `cortex-m` crate as a dependency
             const SCB_CPACR: *mut u32 = 0xE000_ED88 as *mut u32;
             const SCB_CPACR_FPU_ENABLE: u32 = 0b01_01 << 20;
             const SCB_CPACR_FPU_USER: u32 = 0b10_10 << 20;
@@ -932,6 +932,9 @@ pub unsafe extern "C" fn Reset() -> ! {
                 *SCB_CPACR | SCB_CPACR_FPU_ENABLE | SCB_CPACR_FPU_USER,
             );
 
+            cortex_m::asm::dsb();
+            cortex_m::asm::isb();
+
             // this is used to prevent the compiler from inlining the user `main` into the reset
             // handler. Inlining can cause the FPU instructions in the user `main` to be executed
             // before enabling the FPU, and that would produce a hard to diagnose hard fault at