driver_systick.c

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/*! \file driver_systick.c
    \brief Encapsulates the ARM sysTick counter, which is used for benchmarking
*/

#include "sensor_fusion.h"
#include "drivers.h"

// SysTick register definitions based on CMSIS definitions for same
#define SYST_CSR    SysTick->CTRL   // SysTick Control & Status Register
#define SYST_RVR    SysTick->LOAD   // SysTick Reload Value Register
#define SYST_CVR    SysTick->VAL    // SysTick Current Value Register

// ARM-core specific function that enables the ARM systick timer on Kinetis uCs.
// this is purely for algorithm benchmarking and can either be deleted or re-written for use on other uCs.
// the systick clock frequency for each uC are defined as CORE_SYSTICK_HZ in types.h.

// the timer is 24 bit so allows measurement of intervals up to 2^24/CORE_SYSTICK_HZ secs=0.35s for a 48MHz uC.
void ARM_systick_enable(void)
{
    SYST_CSR = 0x5u;        // enable systick from internal clock
    SYST_RVR = 0x00FFFFFFu; // set reload to maximum 24 bit value
    return;
}

// ARM-core specific function to store the current systick timer ticks for benchmarking
void ARM_systick_start_ticks(int32 *pstart)
{
    // store the 24 bit systick timer
    *pstart = SYST_CVR & 0x00FFFFFF;

    return;
}

// ARM-core specific function to compute the elapsed systick timer ticks for benchmarking
int32 ARM_systick_elapsed_ticks(int32 start_ticks)
{
    int32 elapsed_ticks;

    // subtract the stored start ticks and check for wraparound down through zero
    elapsed_ticks = start_ticks - (SYST_CVR & 0x00FFFFFF);
    if (elapsed_ticks < 0) elapsed_ticks += SYST_RVR;

    return elapsed_ticks;
}

void ARM_systick_delay_ms(uint32 iSystemCoreClock, uint32 delay_ms)
{
    int32 istart_ticks; // start ticks on entry
    int32 ielapsed_ticks;   // elapsed ticks
    int16 i;        // loop counter

    // loop for requested number of ms
    for (i = 0; i < delay_ms; i++)
    {
        // loop until 1ms has elapsed
        ARM_systick_start_ticks(&istart_ticks);
        do
        {
            ielapsed_ticks = ARM_systick_elapsed_ticks(istart_ticks);
        } while (ielapsed_ticks < iSystemCoreClock / 1000);
    }

    return;
}