Merge #116

116: Add SysTick flags r=adamgreig a=qwerty19106

CMSIS core headers contains SCB_ICSR_PENDSVSET_*** and SCB_ICSR_PENDSTSET_*** definitions, which I need in my projects. In CMSIS it is used to check, set and clear this flags (rtx_core_cm.h and os_systick.c).

I suggest adding it to scb.rs. I put initial commit, but I need help to add compiler barriers where its are needed.

For details, see CMSIS:
[CMSIS_5/CMSIS/Core/Include/core_cm3.h](https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/Core/Include/core_cm3.h)  (or other core_cm{X}.h)
[CMSIS_5/CMSIS/RTOS2/RTX/Source/rtx_core_cm.h)](https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/RTOS2/RTX/Source/rtx_core_cm.h)
[CMSIS_5/CMSIS/RTOS2/Source/os_systick.c)](https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/RTOS2/Source/os_systick.c)

FIX: I have not seen that PENDSV is already added. I review PENDST code to be like PENDSV.


Co-authored-by: qwerty19106 <qwerty19106@gmail.com>

src/peripheral/scb.rs

@@ -7,9 +7,9 @@ use volatile_register::RW;
 #[cfg(not(armv6m))]
 use super::cpuid::CsselrCacheType;
 #[cfg(not(armv6m))]
-use super::CPUID;
-#[cfg(not(armv6m))]
 use super::CBP;
+#[cfg(not(armv6m))]
+use super::CPUID;
 use super::SCB;
 
 /// Register block
@@ -604,13 +604,18 @@ impl SCB {
     /// Initiate a system reset request to reset the MCU
     pub fn system_reset(&mut self) -> ! {
         ::asm::dsb();
-        unsafe { self.aircr.modify(|r|
-            SCB_AIRCR_VECTKEY | // otherwise the write is ignored
+        unsafe {
+            self.aircr.modify(
+                |r| {
+                    SCB_AIRCR_VECTKEY | // otherwise the write is ignored
             r & SCB_AIRCR_PRIGROUP_MASK | // keep priority group unchanged
-            SCB_AIRCR_SYSRESETREQ // set the bit
-        ) };
+            SCB_AIRCR_SYSRESETREQ
+                }, // set the bit
+            )
+        };
         ::asm::dsb();
-        loop { // wait for the reset
+        loop {
+            // wait for the reset
             ::asm::nop(); // avoid rust-lang/rust#28728
         }
     }
@@ -619,6 +624,9 @@ impl SCB {
 const SCB_ICSR_PENDSVSET: u32 = 1 << 28;
 const SCB_ICSR_PENDSVCLR: u32 = 1 << 27;
 
+const SCB_ICSR_PENDSTSET: u32 = 1 << 26;
+const SCB_ICSR_PENDSTCLR: u32 = 1 << 25;
+
 impl SCB {
     /// Set the PENDSVSET bit in the ICSR register which will pend the PendSV interrupt
     pub fn set_pendsv() {
@@ -629,9 +637,7 @@ impl SCB {
 
     /// Check if PENDSVSET bit in the ICSR register is set meaning PendSV interrupt is pending
     pub fn is_pendsv_pending() -> bool {
-        unsafe {
-            (*Self::ptr()).icsr.read() & SCB_ICSR_PENDSVSET == SCB_ICSR_PENDSVSET
-        }
+        unsafe { (*Self::ptr()).icsr.read() & SCB_ICSR_PENDSVSET == SCB_ICSR_PENDSVSET }
     }
 
     /// Set the PENDSVCLR bit in the ICSR register which will clear a pending PendSV interrupt
@@ -640,4 +646,26 @@ impl SCB {
             (*Self::ptr()).icsr.write(SCB_ICSR_PENDSVCLR);
         }
     }
+
+    /// Set the PENDSTCLR bit in the ICSR register which will clear a pending SysTick interrupt
+    #[inline]
+    pub fn set_pendst() {
+        unsafe {
+            (*Self::ptr()).icsr.write(SCB_ICSR_PENDSTSET);
+        }
+    }
+
+    /// Check if PENDSTSET bit in the ICSR register is set meaning SysTick interrupt is pending
+    #[inline]
+    pub fn is_pendst_pending() -> bool {
+        unsafe { (*Self::ptr()).icsr.read() & SCB_ICSR_PENDSTSET == SCB_ICSR_PENDSTSET }
+    }
+
+    /// Set the PENDSTCLR bit in the ICSR register which will clear a pending SysTick interrupt
+    #[inline]
+    pub fn clear_pendst() {
+        unsafe {
+            (*Self::ptr()).icsr.write(SCB_ICSR_PENDSTCLR);
+        }
+    }
 }