delay.c

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/************************************************************************//**
 * \file    heivs/delay.c
 * \brief   simple delays
 * \author  marc dot pignat at hevs dot ch
 ***************************************************************************/

#include "heivs/delay.h"
#include "stm32/system_stm32f4xx.h"
#include "stm32/stm32f4xx.h"
#include "cmsis/core_cm4.h"

void delay_wait_ms(uint32_t ms)
{
    uint32_t i;
    for (i = 0 ; i < ms ; i++)
    {
        delay_wait_us(1000);
    }
}

/**
 * \brief Delay loop
 *
 * \param n wait for 3*n CPU clocks
 */
__attribute__ ((naked))
static void _delay_loop(uint32_t n)
{
    asm volatile
    (
        "1:                     \n"
        "   subs.n  %0, #1      \n" /* This is one clock */
        "   bne.n   1b          \n" /* 1+P here is 2 clocks (destination is know and a 16-bit instruction) */
        "   bx      lr          \n"
        :
        : "r" (n)
        : "cc"
    );
}

void delay_wait_us(uint32_t us)
{
    uint32_t hz;
    uint32_t mhz;
    uint32_t i;

    if (us > 1000)
    {
        /**
         * What a looooong wait, call the milisecond version after rounding up
         */
        delay_wait_ms((us+999)/1000);
        return;
    }

    /**
     * Split clock between Hz and MHz
     */
    mhz = SystemClock.hclk / (1000*1000);
    hz = SystemClock.hclk % (1000*1000);

    /* Multiply by us, can't overflow because us <= 1000 */
    hz *= us;
    hz /= (1000*1000);

    /* Convert to the number of iteration */
    i = mhz * us;
    i += (hz * us) / (1000 * 1000);

    /* Divide by the number of clocks in a loop, see: the _delay_loop ;) */
    i /= 3;

    /**
     * The wait loop is in the form (--i > 0){}, so if i is zero, this loop will
     * be far too long.
     * There is only two way of falling here, clock or us are zero.
     */
    if (i == 0)
    {
        return;
    }

    _delay_loop(i);
}