使用下面的stopwatch_delay(ticks)來完成延遲.它使用STM32的DWT_CYCCNT寄存器,該寄存器專門用于計(jì)算位于地址0xE0001004的實(shí)際時鐘周期.

要驗(yàn)證延遲準(zhǔn)確性(請參閱main),您可以調(diào)用STOPWATCH_START,運(yùn)行stopwatch_delay(ticks),然后調(diào)用STOPWATCH_STOP并使用CalcNanosecondsFromStopwatch(m_nStart,m_nStop)進(jìn)行驗(yàn)證.根據(jù)需要調(diào)整刻度.

uint32_t m_nStart; //DEBUG Stopwatch start cycle counter value

uint32_t m_nStop; //DEBUG Stopwatch stop cycle counter value

#define DEMCR_TRCENA 0x01000000

/* Core Debug registers */

#define DEMCR (*((volatile uint32_t *)0xE000EDFC))

#define DWT_CTRL (*(volatile uint32_t *)0xe0001000)

#define CYCCNTENA (1<<0)

#define DWT_CYCCNT ((volatile uint32_t *)0xE0001004)

#define CPU_CYCLES *DWT_CYCCNT

#define STOPWATCH_START { m_nStart = *((volatile unsigned int *)0xE0001004);}

#define STOPWATCH_STOP { m_nStop = *((volatile unsigned int *)0xE0001004);}

static inline void stopwatch_reset(void)

{

/* Enable DWT */

DEMCR |= DEMCR_TRCENA;

*DWT_CYCCNT = 0;

/* Enable CPU cycle counter */

DWT_CTRL |= CYCCNTENA;

}

static inline uint32_t stopwatch_getticks()

{

return CPU_CYCLES;

}

static inline void stopwatch_delay(uint32_t ticks)

{

uint32_t end_ticks = ticks + stopwatch_getticks();

while(1)

{

if (stopwatch_getticks() >= end_ticks)

break;

}

}

uint32_t CalcNanosecondsFromStopwatch(uint32_t nStart, uint32_t nStop)

{

uint32_t nDiffTicks;

uint32_t nClkTicksPerMicrosec;

nDiffTicks = nStop - nStart;

nDiffTicks *= 1000; // Scale diff by 1000.

nClkTicksPerMicrosec = SystemCoreClock / 1000000; // Convert (clkTicks/sec) to (clkTicks/microsec), SystemCoreClock = 168000000

return nDiffTicks / nClkTicksPerMicrosec; // nanosec = (ticks * 1000) / (clkTicks/microsec)

}

void main(void)

{

int timeDiff = 0;

stopwatch_reset();

STOPWATCH_START;

run_my_function();

STOPWATCH_STOP;

timeDiff = CalcNanosecondsFromStopwatch(m_nStart, m_nStop);

printf("My function took %d nanoseconds\n", timeDiff);

}

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