Merge branch 'aaa' into ide-1.5.x

Fixes #1388
Fixes #1301

Author: cmaglie

hardware/arduino/sam/cores/arduino/wiring.c

@@ -28,20 +28,50 @@ uint32_t millis( void )
 	return GetTickCount() ;
 }
 
+// Interrupt-compatible version of micros
+// Theory: repeatedly take readings of SysTick counter, millis counter and SysTick interrupt pending flag.
+// When it appears that millis counter and pending is stable and SysTick hasn't rolled over, use these 
+// values to calculate micros. If there is a pending SysTick, add one to the millis counter in the calculation.
 uint32_t micros( void )
 {
-    uint32_t ticks ;
-    uint32_t count ;
+    uint32_t ticks, ticks2;
+    uint32_t pend, pend2;
+    uint32_t count, count2;
+
+    ticks2  = SysTick->VAL;
+    pend2   = !!((SCB->ICSR & SCB_ICSR_PENDSTSET_Msk)||((SCB->SHCSR & SCB_SHCSR_SYSTICKACT_Msk)))  ;
+    count2  = GetTickCount();
 
-    SysTick->CTRL;
     do {
-        ticks = SysTick->VAL;
-        count = GetTickCount();
-    } while (SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk);
+        ticks=ticks2;
+        pend=pend2;
+        count=count2;
+        ticks2  = SysTick->VAL;
+        pend2   = !!((SCB->ICSR & SCB_ICSR_PENDSTSET_Msk)||((SCB->SHCSR & SCB_SHCSR_SYSTICKACT_Msk)))  ;
+        count2  = GetTickCount();
+    } while ((pend != pend2) || (count != count2) || (ticks < ticks2));
 
-    return count * 1000 + (SysTick->LOAD + 1 - ticks) / (SystemCoreClock/1000000) ;
+    return ((count+pend) * 1000) + (((SysTick->LOAD  - ticks)*(1048576/(F_CPU/1000000)))>>20) ; 
+    // this is an optimization to turn a runtime division into two compile-time divisions and 
+    // a runtime multiplication and shift, saving a few cycles
 }
 
+// original function:
+// uint32_t micros( void )
+// {
+//     uint32_t ticks ;
+//     uint32_t count ;
+// 
+//     SysTick->CTRL;
+//     do {
+//         ticks = SysTick->VAL;
+//         count = GetTickCount();
+//     } while (SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk);
+// 
+//     return count * 1000 + (SysTick->LOAD + 1 - ticks) / (SystemCoreClock/1000000) ;
+// }
+
+
 void delay( uint32_t ms )
 {
     uint32_t end = GetTickCount() + ms;