File content as of revision 162:16168a1438f3:

/*
 * 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 "nrf_drv_config.h"
#include "lp_ticker_api.h"


//------------------------------------------------------------------------------
// 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;

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

    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 (__ICCARM__)) && defined(TARGET_MCU_NRF51822)//IAR
__stackless __task 
#endif
void RTC1_IRQHandler(void);

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

    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)
        APP_IRQ_PRIORITY_LOWEST
#endif
        );

    nrf_rtc_task_trigger(COMMON_RTC_INSTANCE, NRF_RTC_TASK_START);

    m_common_rtc_enabled = true;
}

uint32_t common_rtc_32bit_ticks_get(void)
{
    uint32_t 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);
    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);

    // 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);
}
//------------------------------------------------------------------------------


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_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;

/*
 RTX provide the following definitions which are used by the tick code:
   * os_trv: The number (minus 1) of clock cycle between two tick.
   * os_clockrate: Time duration between two ticks (in us).
   * OS_Tick_Handler: The function which handle a tick event.
     This function is special because it never returns.
 Those definitions are used by the code which handle the os tick.
 To allow compilation of us_ticker programs without RTOS, those symbols are
 exported from this module as weak ones.
 */
MBED_WEAK uint32_t const os_trv;
MBED_WEAK uint32_t const os_clockrate;
MBED_WEAK void OS_Tick_Handler() { }


#if defined (__CC_ARM)         /* ARMCC Compiler */

__asm void COMMON_RTC_IRQ_HANDLER(void)
{
    IMPORT  OS_Tick_Handler
    IMPORT  common_rtc_irq_handler

    /**
     * Chanel 1 of RTC1 is used by RTX as a systick.
     * If the compare event on channel 1 is set, then branch to OS_Tick_Handler.
     * Otherwise, just execute common_rtc_irq_handler.
     * This function has to be written in assembly and tagged as naked because OS_Tick_Handler
     * will never return.
     * A c function would put lr on the stack before calling OS_Tick_Handler and this value
     * would never been dequeued.
     *
     * \code
     * void COMMON_RTC_IRQ_HANDLER(void) {
         if(NRF_RTC1->EVENTS_COMPARE[1]) {
             // never return...
             OS_Tick_Handler();
         } else {
             common_rtc_irq_handler();
         }
       }
     * \endcode
     */
    ldr r0,=0x40011144
    ldr r1, [r0, #0]
    cmp r1, #0
    beq US_TICKER_HANDLER
    bl OS_Tick_Handler
US_TICKER_HANDLER
    push {r3, lr}
    bl common_rtc_irq_handler
    pop {r3, pc}
    ; ALIGN ;
}

#elif defined (__GNUC__)        /* GNU Compiler */

__attribute__((naked)) void COMMON_RTC_IRQ_HANDLER(void)
{
    /**
     * Chanel 1 of RTC1 is used by RTX as a systick.
     * If the compare event on channel 1 is set, then branch to OS_Tick_Handler.
     * Otherwise, just execute common_rtc_irq_handler.
     * This function has to be written in assembly and tagged as naked because OS_Tick_Handler
     * will never return.
     * A c function would put lr on the stack before calling OS_Tick_Handler and this value
     * would never been dequeued.
     *
     * \code
     * void COMMON_RTC_IRQ_HANDLER(void) {
         if(NRF_RTC1->EVENTS_COMPARE[1]) {
             // never return...
             OS_Tick_Handler();
         } else {
             common_rtc_irq_handler();
         }
       }
     * \endcode
     */
    __asm__ (
        "ldr r0,=0x40011144\n"
        "ldr r1, [r0, #0]\n"
        "cmp r1, #0\n"
        "beq US_TICKER_HANDLER\n"
        "bl OS_Tick_Handler\n"
    "US_TICKER_HANDLER:\n"
        "push {r3, lr}\n"
        "bl common_rtc_irq_handler\n"
        "pop {r3, pc}\n"
        "nop"
    );
}

#elif defined (__ICCARM__)//IAR
void common_rtc_irq_handler(void);

__stackless __task void COMMON_RTC_IRQ_HANDLER(void)
{
    uint32_t temp;

    __asm volatile(
    "   ldr  %[temp], [%[reg2check]] \n"
    "   cmp  %[temp], #0             \n"
    "   beq  1f                      \n"
    "   bl.w OS_Tick_Handler            \n"
    "1:                             \n"
    "   push {r3, lr}\n"
    "   blx %[rtc_irq] \n"
    "   pop {r3, pc}\n"

    : /* Outputs */
    [temp] "=&r"(temp)
    : /* Inputs */
    [reg2check] "r"(0x40011144),
    [rtc_irq] "r"(common_rtc_irq_handler)
    : /* Clobbers */
    "cc"
    );
    (void)temp;
}


#else

#error Compiler not supported.
#error Provide a definition of COMMON_RTC_IRQ_HANDLER.

/*
 * Chanel 1 of RTC1 is used by RTX as a systick.
 * If the compare event on channel 1 is set, then branch to OS_Tick_Handler.
 * Otherwise, just execute common_rtc_irq_handler.
 * This function has to be written in assembly and tagged as naked because OS_Tick_Handler
 * will never return.
 * A c function would put lr on the stack before calling OS_Tick_Handler and this value
 * will never been dequeued. After a certain time a stack overflow will happen.
 *
 * \code
 * void COMMON_RTC_IRQ_HANDLER(void) {
     if(NRF_RTC1->EVENTS_COMPARE[1]) {
         // never return...
         OS_Tick_Handler();
     } else {
         common_rtc_irq_handler();
     }
   }
 * \endcode
 */

#endif

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

    if (os_clockrate != 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_trv + 1;
    } 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
 */
int os_tick_init (void)
{
    common_rtc_init();
    nrf_rtc_int_enable(COMMON_RTC_INSTANCE, OS_TICK_INT_MASK);

    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL, 0);
    register_next_tick();

    return nrf_drv_get_IRQn(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 os_tick_irqack(void)
{
    clear_tick_interrupt();
    register_next_tick();
}

/**
 * Returns the overflow flag of the alternative hardware timer.
 * @note This function is exposed by RTX kernel.
 * @return 1 if the timer has overflowed and 0 otherwise.
 */
uint32_t os_tick_ovf(void) {
    uint32_t current_counter = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
    uint32_t next_tick_cc_value = nrf_rtc_cc_get(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL);

    return is_in_wrapped_range(previous_tick_cc_value, next_tick_cc_value, current_counter) ? 0 : 1;
}

/**
 * Return the value of the alternative hardware timer.
 * @note The documentation is not very clear about what is expected as a result,
 * is it an ascending counter, a descending one ?
 * None of this is specified.
 * The default systick is a descending counter and this function return values in
 * descending order, even if the internal counter used is an ascending one.
 * @return the value of the alternative hardware timer.
 */
uint32_t os_tick_val(void) {
    uint32_t current_counter = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
    uint32_t next_tick_cc_value = nrf_rtc_cc_get(COMMON_RTC_INSTANCE, OS_TICK_CC_CHANNEL);

    // do not use os_tick_ovf because its counter value can be different
    if(is_in_wrapped_range(previous_tick_cc_value, next_tick_cc_value, current_counter)) {
        if (next_tick_cc_value > previous_tick_cc_value) {
            return next_tick_cc_value - current_counter;
        } else if(current_counter <= next_tick_cc_value) {
            return next_tick_cc_value - current_counter;
        } else {
            return next_tick_cc_value + (MAX_RTC_COUNTER_VAL - current_counter);
        }
    } else {
        // use (os_trv + 1) has the base step, can be totally inacurate ...
        uint32_t clock_cycles_by_tick = os_trv + 1;

        // if current counter has wrap arround, add the limit to it.
        if (current_counter < next_tick_cc_value) {
            current_counter = current_counter + MAX_RTC_COUNTER_VAL;
        }

        return clock_cycles_by_tick - ((current_counter - next_tick_cc_value) % clock_cycles_by_tick);
    }

}

#endif // defined(TARGET_MCU_NRF51822)