Generating nanosecond delay in C on STM32

问题

I am using STM32F2 controller and I am interfacing with an ST7036 LCD display via 8 bit parallel interface.

The datasheet says there should be a 20 nano second delay between address hold and setup time.

How do I generate a 20 nanosecond delay in C?

回答1:

Use stopwatch_delay(ticks) below to accomplish your delays. It uses the STM32's DWT_CYCCNT register, which is specifically designed to count actual clock ticks, located at address 0xE0001004.

To verify the delay accuracy (see main), you can call STOPWATCH_START, run stopwatch_delay(ticks), then call STOPWATCH_STOP and verify with CalcNanosecondsFromStopwatch(m_nStart, m_nStop). Adjust ticks as needed.

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);
}

回答2:

The first specification I found of Stm32f2 assumes a clock frequency of 120 MHz. That's about 8ns per clock cycle. You would need about three single cycle instructions between successive write or read/write operations. In C, a++; will probably do (if a is located in stack).

回答3:

You should look into the FSMC peripheral available in your chip. While the configuration might be complicated, especially if you're not dropping in a memory part that it was designed for, you might find that your parallel interfaced device maps pretty well to one of the memory interface modes.

These sorts of external memory controllers must have a bunch of configurable timing options to support the range of different memory chips out there so you'll be able to guarantee the timings required by your datasheet.

The nice benefit of being able to do this is your LCD will then seem like any old memory mapped peripheral, abstracting away the lower level interfacing details.

来源：https://stackoverflow.com/questions/13379220/generating-nanosecond-delay-in-c-on-stm32

标签

stm32

lcd