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Changed micros() to work in interrupts

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This commit is contained in:
stimmer
2013-04-27 16:47:28 +01:00
committed by Cristian Maglie
parent 33a7279a7d
commit 00bc1639c4
1 changed files with 37 additions and 7 deletions
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44
hardware/arduino/sam/cores/arduino/wiring.c
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@ -28,20 +28,50 @@ uint32_t millis( void )
return GetTickCount() ; 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 micros( void )
{ {
uint32_t ticks ; uint32_t ticks, ticks2;
uint32_t count ; 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 { do {
ticks = SysTick->VAL; ticks=ticks2;
count = GetTickCount(); pend=pend2;
} while (SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk); 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 ) void delay( uint32_t ms )
{ {
uint32_t end = GetTickCount() + ms; uint32_t end = GetTickCount() + ms;