mbed-os/targets/TARGET_NORDIC/TARGET_NRF5/us_ticker.c

/*
 * Copyright (c) 2013 Nordic Semiconductor ASA
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright notice, this list
 *      of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form, except as embedded into a Nordic Semiconductor ASA
 *      integrated circuit in a product or a software update for such product, must reproduce
 *      the above copyright notice, this list of conditions and the following disclaimer in
 *      the documentation and/or other materials provided with the distribution.
 *
 *   3. Neither the name of Nordic Semiconductor ASA nor the names of its contributors may be
 *      used to endorse or promote products derived from this software without specific prior
 *      written permission.
 *
 *   4. This software, with or without modification, must only be used with a
 *      Nordic Semiconductor ASA integrated circuit.
 *
 *   5. Any software provided in binary or object form under this license must not be reverse
 *      engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include "us_ticker_api.h"
#include "common_rtc.h"
#include "app_util.h"
#include "nrf_drv_common.h"
#include "lp_ticker_api.h"
#include "mbed_critical.h"

#if defined(NRF52_ERRATA_20)
    #include "softdevice_handler.h"
#endif

//------------------------------------------------------------------------------
// Common stuff used also by lp_ticker and rtc_api (see "common_rtc.h").
//
#include "app_util_platform.h"

bool              m_common_rtc_enabled = false;
uint32_t volatile m_common_rtc_overflows = 0;

__STATIC_INLINE void rtc_ovf_event_check(void)
{
    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW)) {
        nrf_rtc_event_clear(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);
        // Don't disable this event. It shall occur periodically.

        ++m_common_rtc_overflows;
    }
}

#if defined(TARGET_MCU_NRF51822)
void common_rtc_irq_handler(void)
#else
void COMMON_RTC_IRQ_HANDLER(void)
#endif
{

    rtc_ovf_event_check();

    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, US_TICKER_EVENT)) {
        us_ticker_irq_handler();
    }

#if DEVICE_LOWPOWERTIMER
    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, LP_TICKER_EVENT)) {

        lp_ticker_irq_handler();
    }
#endif
}

// Function for fix errata 20: RTC Register values are invalid
__STATIC_INLINE void errata_20(void)
{
#if defined(NRF52_ERRATA_20)
    if (!softdevice_handler_is_enabled())
    {
        NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
        NRF_CLOCK->TASKS_LFCLKSTART    = 1;

        while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
        {
        }
    }
    NRF_RTC1->TASKS_STOP = 0;
#endif
}

void RTC1_IRQHandler(void);

void common_rtc_init(void)
{
    if (m_common_rtc_enabled) {
        return;
    }

    errata_20();

    NVIC_SetVector(RTC1_IRQn, (uint32_t)RTC1_IRQHandler);
    
    // RTC is driven by the low frequency (32.768 kHz) clock, a proper request
    // must be made to have it running.
    // Currently this clock is started in 'SystemInit' (see "system_nrf51.c"
    // or "system_nrf52.c", respectively).

    nrf_rtc_prescaler_set(COMMON_RTC_INSTANCE, 0);

    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, US_TICKER_EVENT);
#if defined(TARGET_MCU_NRF51822)
    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, OS_TICK_EVENT);
#endif
#if DEVICE_LOWPOWERTIMER
    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, LP_TICKER_EVENT);
#endif
    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);

    // Interrupts on all related events are enabled permanently. Particular
    // events will be enabled or disabled as needed (such approach is more
    // energy efficient).
    nrf_rtc_int_enable(COMMON_RTC_INSTANCE,
#if DEVICE_LOWPOWERTIMER
        LP_TICKER_INT_MASK |
#endif
        US_TICKER_INT_MASK |
        NRF_RTC_INT_OVERFLOW_MASK);

    // This event is enabled permanently, since overflow indications are needed
    // continuously.
    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, NRF_RTC_INT_OVERFLOW_MASK);
    // All other relevant events are initially disabled.
    nrf_rtc_event_disable(COMMON_RTC_INSTANCE,
#if defined(TARGET_MCU_NRF51822)
        OS_TICK_INT_MASK |
#endif
#if DEVICE_LOWPOWERTIMER
        LP_TICKER_INT_MASK |
#endif
        US_TICKER_INT_MASK);

    nrf_drv_common_irq_enable(nrf_drv_get_IRQn(COMMON_RTC_INSTANCE),
#ifdef NRF51
        APP_IRQ_PRIORITY_LOW
#elif defined(NRF52) || defined(NRF52840_XXAA)
        APP_IRQ_PRIORITY_LOWEST
#endif
        );

    nrf_rtc_task_trigger(COMMON_RTC_INSTANCE, NRF_RTC_TASK_START);

    m_common_rtc_enabled = true;
}

__STATIC_INLINE void rtc_ovf_event_safe_check(void)
{
    core_util_critical_section_enter();

    rtc_ovf_event_check();

    core_util_critical_section_exit();
}


uint32_t common_rtc_32bit_ticks_get(void)
{
    uint32_t ticks;
    uint32_t prev_overflows;

    do {
        prev_overflows = m_common_rtc_overflows;

        ticks = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
        // The counter used for time measurements is less than 32 bit wide,
        // so its value is complemented with the number of registered overflows
        // of the counter.
        ticks += (m_common_rtc_overflows << RTC_COUNTER_BITS);

        // Check in case that OVF occurred during execution of a RTC handler (apply if call was from RTC handler)
        // m_common_rtc_overflows might been updated in this call.
        rtc_ovf_event_safe_check();

        // If call was made from a low priority level m_common_rtc_overflows might have been updated in RTC handler.
    } while (m_common_rtc_overflows != prev_overflows);

    return ticks;
}

uint64_t common_rtc_64bit_us_get(void)
{
    uint32_t ticks = common_rtc_32bit_ticks_get();
    // [ticks -> microseconds]
    return ROUNDED_DIV(((uint64_t)ticks) * 1000000, RTC_INPUT_FREQ);
}

void common_rtc_set_interrupt(uint32_t us_timestamp, uint32_t cc_channel,
                              uint32_t int_mask)
{
    // The internal counter is clocked with a frequency that cannot be easily
    // multiplied to 1 MHz, therefore besides the translation of values
    // (microsecond <-> ticks) a special care of overflows handling must be
    // taken. Here the 32-bit timestamp value is complemented with information
    // about current the system up time of (ticks + number of overflows of tick
    // counter on upper bits, converted to microseconds), and such 64-bit value
    // is then translated to counter ticks. Finally, the lower 24 bits of thus
    // calculated value is written to the counter compare register to prepare
    // the interrupt generation.
    uint64_t current_time64 = common_rtc_64bit_us_get();
    // [add upper 32 bits from the current time to the timestamp value]
    uint64_t timestamp64 = us_timestamp +
        (current_time64 & ~(uint64_t)0xFFFFFFFF);
    // [if the original timestamp value happens to be after the 32 bit counter
    //  of microsends overflows, correct the upper 32 bits accordingly]
    if (us_timestamp < (uint32_t)(current_time64 & 0xFFFFFFFF)) {
        timestamp64 += ((uint64_t)1 << 32);
    }
    // [microseconds -> ticks, always round the result up to avoid too early
    //  interrupt generation]
    uint32_t compare_value =
        (uint32_t)CEIL_DIV((timestamp64) * RTC_INPUT_FREQ, 1000000);


    core_util_critical_section_enter();
    // The COMPARE event occurs when the value in compare register is N and
    // the counter value changes from N-1 to N. Therefore, the minimal safe
    // difference between the compare value to be set and the current counter
    // value is 2 ticks. This guarantees that the compare trigger is properly
    // setup before the compare condition occurs.
    uint32_t closest_safe_compare = common_rtc_32bit_ticks_get() + 2;
    if ((int)(compare_value - closest_safe_compare) <= 0) {
        compare_value = closest_safe_compare;
    }

    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, cc_channel, RTC_WRAP(compare_value));
    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, int_mask);

    core_util_critical_section_exit();
}
//------------------------------------------------------------------------------


void us_ticker_init(void)
{
    common_rtc_init();
}

uint32_t us_ticker_read()
{
    us_ticker_init();
    return (uint32_t)common_rtc_64bit_us_get();
}

void us_ticker_set_interrupt(timestamp_t timestamp)
{
    common_rtc_set_interrupt(timestamp,
        US_TICKER_CC_CHANNEL, US_TICKER_INT_MASK);
}

void us_ticker_fire_interrupt(void)
{
    uint32_t closest_safe_compare = common_rtc_32bit_ticks_get() + 2;

    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, US_TICKER_CC_CHANNEL, RTC_WRAP(closest_safe_compare));
    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, US_TICKER_INT_MASK);
}

void us_ticker_disable_interrupt(void)
{
    nrf_rtc_event_disable(COMMON_RTC_INSTANCE, US_TICKER_INT_MASK);
}

void us_ticker_clear_interrupt(void)
{
    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, US_TICKER_EVENT);
}


// Since there is no SysTick on NRF51, the RTC1 channel 1 is used as an
// alternative source of RTOS ticks.
#if defined(TARGET_MCU_NRF51822)

#include "mbed_toolchain.h"


#define MAX_RTC_COUNTER_VAL     ((1uL << RTC_COUNTER_BITS) - 1)

/**
 * The value previously set in the capture compare register of channel 1
 */
static uint32_t previous_tick_cc_value = 0;

/* The Period of RTC oscillator, unit [1/RTC1_CONFIG_FREQUENCY] */
static uint32_t os_rtc_period;

/* Variable for frozen RTC1 counter value. It is used when system timer is disabled. */
static uint32_t frozen_sub_tick = 0;
     

#ifdef MBED_CONF_RTOS_PRESENT
    #include "rtx_os.h" //import osRtxInfo, SysTick_Handler()
    
    static inline void clear_tick_interrupt();
#endif

#ifndef RTC1_CONFIG_FREQUENCY
    #define RTC1_CONFIG_FREQUENCY    32678 // [Hz]
#endif



void COMMON_RTC_IRQ_HANDLER(void)
{
    if(nrf_rtc_event_pending(COMMON_RTC_INSTANCE, OS_TICK_EVENT)) {
#ifdef MBED_CONF_RTOS_PRESENT
        clear_tick_interrupt();
        // Trigger the SysTick_Handler just after exit form RTC Handler.
        NVIC_SetPendingIRQ(SWI3_IRQn);

        nrf_gpio_pin_set(11);
#endif
    } else {
        common_rtc_irq_handler();
    }
}


#ifdef MBED_CONF_RTOS_PRESENT
/**
 * Return the next number of clock cycle needed for the next tick.
 * @note This function has been carefully optimized for a systick occurring every 1000us.
 */
static uint32_t get_next_tick_cc_delta()
{
    uint32_t delta = 0;

    if (osRtxConfig.tick_freq != 1000) {
        // In RTX, by default SYSTICK is is used.
        // A tick event is generated  every os_trv + 1 clock cycles of the system timer.
        delta = os_rtc_period;
    } else {
        // If the clockrate is set to 1000us then 1000 tick should happen every second.
        // Unfortunatelly, when clockrate is set to 1000, os_trv is equal to 31.
        // If (os_trv + 1) is used as the delta value between two ticks, 1000 ticks will be
        // generated in 32000 clock cycle instead of 32768 clock cycles.
        // As a result, if a user schedule an OS timer to start in 100s, the timer will start
        // instead after 97.656s
        // The code below fix this issue, a clock rate of 1000s will generate 1000 ticks in 32768
        // clock cycles.
        // The strategy is simple, for 1000 ticks:
        //   * 768 ticks will occur 33 clock cycles after the previous tick
        //   * 232 ticks will occur 32 clock cycles after the previous tick
        // By default every delta is equal to 33.
        // Every five ticks (20%, 200 delta in one second), the delta is equal to 32
        // The remaining (32) deltas equal to 32 are distributed using primes numbers.
        static uint32_t counter = 0;
        if ((counter % 5) == 0 || (counter % 31) == 0 || (counter % 139) == 0 || (counter == 503)) {
            delta = 32;
        } else {
            delta = 33;
        }
        ++counter;
        if (counter == 1000) {
            counter = 0;
        }
    }
    return delta;
}

static inline void clear_tick_interrupt()
{
    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, OS_TICK_EVENT);
    nrf_rtc_event_disable(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK);
}

/**
 * Indicate if a value is included in a range which can be wrapped.
 * @param  begin start of the range
 * @param  end   end of the range
 * @param  val   value to check
 * @return       true if the value is included in the range and false otherwise.
 */
static inline bool is_in_wrapped_range(uint32_t begin, uint32_t end, uint32_t val)
{
    // regular case, begin < end
    // return true if  begin <= val < end
    if (begin < end) {
        if (begin <= val && val < end) {
            return true;
        } else {
            return false;
        }
    } else {
        // In this case end < begin because it has wrap around the limits
        // return false if end < val < begin
        if (end < val && val < begin)  {
            return false;
        } else {
            return true;
        }
    }

}

/**
 * Register the next tick.
 */
static void register_next_tick()
{
    previous_tick_cc_value = nrf_rtc_cc_get(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL);
    uint32_t delta = get_next_tick_cc_delta();
    uint32_t new_compare_value = (previous_tick_cc_value + delta) & MAX_RTC_COUNTER_VAL;

    // Disable irq directly for few cycles,
    // Validation of the new CC value against the COUNTER,
    // Setting the new CC value and enabling CC IRQ should be an atomic operation
    // Otherwise, there is a possibility to set an invalid CC value because
    // the RTC1 keeps running.
    // This code is very short 20-38 cycles in the worst case, it shouldn't
    // disturb softdevice.
    __disable_irq();
    uint32_t current_counter = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);

    // If an overflow occur, set the next tick in COUNTER + delta clock cycles
    if (is_in_wrapped_range(previous_tick_cc_value, new_compare_value, current_counter + 1) == false) {
        new_compare_value = current_counter + delta;
    }
    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL, new_compare_value);
    // Enable generation of the compare event for the value set above (this
    // event will trigger the interrupt).
    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK);
    __enable_irq();
}


/**
 * Initialize alternative hardware timer as RTX kernel timer
 * This function is directly called by RTX.
 * @note this function shouldn't be called directly.
 * @return  IRQ number of the alternative hardware timer
 */
int32_t osRtxSysTimerSetup(void)
{
    common_rtc_init();
    
    os_rtc_period = (RTC1_CONFIG_FREQUENCY) / osRtxConfig.tick_freq;

    return nrf_drv_get_IRQn(COMMON_RTC_INSTANCE);
}

// Start SysTickt timer emulation
void osRtxSysTimerEnable(void)
{
    nrf_rtc_int_enable(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK);

    uint32_t current_cnt = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL, current_cnt);
    register_next_tick();

    NVIC_SetVector(SWI3_IRQn, (uint32_t)SysTick_Handler);
    NVIC_SetPriority(SWI3_IRQn, (1UL << __NVIC_PRIO_BITS) - 1UL); /* set Priority for Emulated Systick Interrupt */
    NVIC_EnableIRQ(SWI3_IRQn);
}

// Stop SysTickt timer emulation
void osRtxSysTimerDisable(void)
{
    nrf_rtc_int_disable(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK);
    
    // RTC1 is free runing. osRtxSysTimerGetCount will return proper frozen value
    // thanks to geting frozen value instead of RTC1 counter value
    frozen_sub_tick = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
}



/**
 * Acknowledge the tick interrupt.
 * This function is called by the function OS_Tick_Handler of RTX.
 * @note this function shouldn't be called directly.
 */
void osRtxSysTimerAckIRQ(void)
{
    register_next_tick();
}

// provide a free running incremental value over the entire 32-bit range
uint32_t osRtxSysTimerGetCount(void)
{
    uint32_t current_cnt;
    uint32_t sub_tick;

    if (nrf_rtc_int_is_enabled(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK)) {
        // system timer is enabled
        current_cnt = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
        
        if (current_cnt >= previous_tick_cc_value) {
            //0      prev      current      MAX
            //|------|---------|------------|---->
            sub_tick = current_cnt - previous_tick_cc_value;
        } else {
            //0      current   prev         MAX
            //|------|---------|------------|---->
            sub_tick = MAX_RTC_COUNTER_VAL - previous_tick_cc_value + current_cnt;
        }
    } else {   // system timer is disabled
        sub_tick = frozen_sub_tick;
    }
    
    return (os_rtc_period *  osRtxInfo.kernel.tick) + sub_tick;
}

// Timer Tick frequency
uint32_t osRtxSysTimerGetFreq (void) {
    return RTC1_CONFIG_FREQUENCY;
}

#endif // #ifdef MBED_CONF_RTOS_PRESENT

#endif // defined(TARGET_MCU_NRF51822)