File content as of revision 175:b96e65c34a4d:

/**
 *******************************************************************************
 * @file    rtc.c
 * @brief Implementation of a Rtc driver
 * @internal
 * @author  ON Semiconductor
 * $Rev: 3525 $
 * $Date: 2015-07-20 15:24:25 +0530 (Mon, 20 Jul 2015) $
 ******************************************************************************
 * Copyright 2016 Semiconductor Components Industries LLC (d/b/a �ON Semiconductor�).
 * All rights reserved.  This software and/or documentation is licensed by ON Semiconductor
 * under limited terms and conditions.  The terms and conditions pertaining to the software
 * and/or documentation are available at http://www.onsemi.com/site/pdf/ONSEMI_T&C.pdf
 * (�ON Semiconductor Standard Terms and Conditions of Sale, Section 8 Software�) and
 * if applicable the software license agreement.  Do not use this software and/or
 * documentation unless you have carefully read and you agree to the limited terms and
 * conditions.  By using this software and/or documentation, you agree to the limited
 * terms and conditions.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS".  NO WARRANTIES, WHETHER EXPRESS, IMPLIED
 * OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
 * ON SEMICONDUCTOR SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL,
 * INCIDENTAL, OR CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
 * @endinternal
 *
 * @ingroup rtc
 *
 * @details
 * A real-time clock (RTC) is a computer clock ,that keeps track of the current time.  The heart of the RTC is a series of
 * freely running counters one for each time unit, The series of counters is linked as follows: a roll over event of
 * the seconds counter produces a minutes enable pulse; a roll over event of the minutes counter produces an hours
 * enable pulse, etc.Note that all Counter registers are in an undefined state on power-up.
 * Use the Reset bit in the Control Register to reset the counters to their default values.
 * DIVISOR is the register containing the value to divide the clock frequency to produce 1Hz strobe ; 1Hz strobe is used
 * internally to time the incrementing of the Seconds Counter.
 * There is a set of register to set the values in the counter for each time unit.from where time is start to increment.
 * There is another set of register to set the ALARM ...Each of the Alarm Registers can be programmed with a value that
 * is used to compare to a Counter Register in order to produce an alarm (an interrupt) when the values match.
 * There is a programmable bit in each Alarm Register that determines if the alarm occurs upon a value match, or
 * if the alarm occurs upon a Counter increment condition.
 *
 */
#include "rtc.h"
#include "mbed_assert.h"
#include "lp_ticker_api.h"

static volatile uint64_t last_time_read;

/**
 * Convert sub seconds ticks to micro seconds.
 * The clock running at 32kHz, a tick is 1/32768 of a second.
 */
static inline uint32_t ticks_to_us(uint16_t ticks) {
	return (((uint64_t)ticks * RTC_SEC_TO_US) / RTC_CLOCK_HZ);
}

/**
 * Convert us into sub seconds ticks.
 * @note result might be troncated to be in the range [0 - RTC_SUB_SEC_MASK].
 */
static inline uint16_t us_to_ticks(uint32_t us) {
	return (((uint64_t) us * RTC_CLOCK_HZ) / RTC_SEC_TO_US) & RTC_SUB_SEC_MASK;
}

#define RTC_TICK_THRESHOLD 5 

/* See rtc.h for details */
void fRtcInit(void)
{
    CLOCK_ENABLE(CLOCK_RTC);             /* enable rtc peripheral */
    CLOCKREG->CCR.BITS.RTCEN = True;     /* Enable RTC clock 32K */

    /* Reset RTC control register */
    RTCREG->CONTROL.WORD = 0;

    /* Initialize all counters */
    RTCREG->SECOND_COUNTER = 0;
    RTCREG->SUB_SECOND_COUNTER = 0;
    RTCREG->SECOND_ALARM = 0;
    RTCREG->SUB_SECOND_ALARM = 0;
    last_time_read = 0;

    /* Reset RTC Status register */
    RTCREG->STATUS.WORD = 0;

    /* Clear interrupt status */
    RTCREG->INT_CLEAR.WORD = (
        (1 << RTC_INT_CLR_SUB_SEC_BIT_POS) | 
        (1 << RTC_INT_CLR_SEC_BIT_POS)
    );

    /* Wait previous write to complete */
    while(RTCREG->STATUS.BITS.BSY_CTRL_REG_WRT == True);
    /* Start sec & sub_sec counter */
    RTCREG->CONTROL.WORD |= (
        (True << RTC_CONTROL_SUBSEC_CNT_START_BIT_POS) |
        (True << RTC_CONTROL_SEC_CNT_START_BIT_POS)
    );

    /* enable interruption associated with the rtc at NVIC level */
    NVIC_SetVector(Rtc_IRQn,(uint32_t) fRtcHandler); /* TODO define lp_ticker_isr */
    NVIC_ClearPendingIRQ(Rtc_IRQn);
    NVIC_EnableIRQ(Rtc_IRQn);

    /* Wait for RTC to finish writing register */
    while(RTCREG->STATUS.BITS.BSY_CTRL_REG_WRT == True);
}

/* See rtc.h for details */
void fRtcFree(void)
{
    /* Disable interrupts and counter */
    RTCREG->CONTROL.WORD = 0;

    /* disable interruption associated with the rtc */
    NVIC_DisableIRQ(Rtc_IRQn);

    /* Wait for RTC to finish writing register */
    while(RTCREG->STATUS.BITS.BSY_CTRL_REG_WRT == True);
}

/* See rtc.h for details */
void fRtcSetInterrupt(uint32_t timestamp)
{
	uint64_t current_time = fRtcRead();

	uint64_t full_timestamp = (current_time & ~UINT32_MAX) | timestamp;
	if ( (uint32_t)current_time > timestamp) {
		full_timestamp += ((uint64_t) UINT32_MAX) + 1;
	}

	uint32_t target_seconds = full_timestamp / RTC_SEC_TO_US;
	uint16_t target_ticks = us_to_ticks(full_timestamp);

	/*
	 * If the interrupt is in more than one second from now then use the
	 * second alarm, otherwise use the subsecond alarm.
	 * In case of the second alarm is used, there is no need to preserve the
	 * remaining subsecond because the irq handler should manage spurious
	 * interrupts (like when the timestamp is in the past). In such case, irq
	 * handler will schedule a new interrupt with the remaining us.
	 */
	NVIC_DisableIRQ(Rtc_IRQn);
	if (target_seconds != RTCREG->SECOND_COUNTER) {
		RTCREG->SECOND_ALARM = target_seconds;

		uint32_t rtc_control = RTCREG->CONTROL.WORD;
		rtc_control |= (1 << RTC_CONTROL_SEC_CNT_INT_BIT_POS); // enable seconds interrupt
		rtc_control &= ~(1 << RTC_CONTROL_SUBSEC_CNT_INT_BIT_POS); // disable sub sec interrupt
		RTCREG->CONTROL.WORD = rtc_control;
	} else {
		uint16_t current_ticks = RTCREG->SUB_SECOND_COUNTER;
		if (current_ticks == target_ticks ||
			((target_ticks > current_ticks) && ((target_ticks - current_ticks) < RTC_TICK_THRESHOLD)) ||
			((target_ticks < current_ticks) && ((RTC_SUB_SEC_MASK - (current_ticks - target_ticks)) < RTC_TICK_THRESHOLD))) {
			// target ticks too close; schedule the interrupt immediately
			NVIC_SetPendingIRQ(Rtc_IRQn);
		} else {
			RTCREG->SUB_SECOND_ALARM = target_ticks;

			uint32_t rtc_control = RTCREG->CONTROL.WORD;
			rtc_control &= ~(1 << RTC_CONTROL_SEC_CNT_INT_BIT_POS); // disable seconds interrupt
			rtc_control |= (1 << RTC_CONTROL_SUBSEC_CNT_INT_BIT_POS); // enable sub sec interrupt
			RTCREG->CONTROL.WORD = rtc_control;
		}
	}
	 NVIC_EnableIRQ(Rtc_IRQn);

     /* Wait for RTC to finish writing register - RTC operates on 32K clock as compared to 32M core*/
     while(RTCREG->STATUS.WORD &
        (
        	(True << RTC_STATUS_SUB_SEC_ALARM_WRT_BIT_POS) |
			(True << RTC_STATUS_SEC_ALARM_WRT_BIT_POS) |
			(True << RTC_STATUS_CONTROL_WRT_BIT_POS)
		)
	);
}

/* See rtc.h for details */
void fRtcDisableInterrupt(void)
{
    NVIC_DisableIRQ(Rtc_IRQn);
}

/* See rtc.h for details */
void fRtcEnableInterrupt(void)
{
    NVIC_EnableIRQ(Rtc_IRQn);
}

/* See rtc.h for details */
void fRtcClearInterrupt(void)
{
    /* Disable subsec/sec interrupt */
    /* Clear sec & sub_sec interrupts */
    RTCREG->INT_CLEAR.WORD = ((True << RTC_INT_CLR_SUB_SEC_BIT_POS) |
                              (True << RTC_INT_CLR_SEC_BIT_POS));
    
    while((RTCREG->STATUS.WORD & ((True << RTC_STATUS_SUB_SEC_INT_CLR_WRT_BIT_POS) |
                                  (True << RTC_STATUS_SEC_INT_CLR_WRT_BIT_POS))));  /* Wait for RTC to finish writing register - RTC operates on 32K clock as compared to 32M core*/
}

/* See rtc.h for details */
uint64_t fRtcRead(void)
{
    /* Hardware Bug fix: The rollover of the sub-second counter initiates the increment of the second counter.
     * That means there is one cycle where the sub-second has rolled back to zero and the second counter has not incremented
     * and a read during that cycle will be incorrect.  That will occur for one RTC cycle and that is about 31us of exposure.
     * If you read a zero in the sub-second counter then increment the second counter by 1.
     * Alternatively, subtract 1 from the Sub-seconds counter to align the Second and Sub-Second rollover.
     */
	uint32_t seconds = RTCREG->SECOND_COUNTER;
    uint16_t ticks = (RTCREG->SUB_SECOND_COUNTER - 1) & SUB_SEC_MASK;

    /*
     * If seconds has changed while reading ticks, read them both again.
     */
    while (seconds != RTCREG->SECOND_COUNTER) {
        seconds = RTCREG->SECOND_COUNTER;
        ticks = (RTCREG->SUB_SECOND_COUNTER - 1) & SUB_SEC_MASK;
    }

    uint64_t current_time = ((uint64_t) seconds *  RTC_SEC_TO_US) + ticks_to_us(ticks);

    /*check that the time did not go backwards */
	MBED_ASSERT(current_time >= last_time_read);
    last_time_read = current_time;

    return current_time;
}

/* See rtc.h for details */
void fRtcWrite(uint64_t RtcTimeus)
{
    uint32_t Second    = False;
    uint16_t SubSecond = False;
    /* Stop RTC */
    RTCREG->CONTROL.WORD &= ~((True << RTC_CONTROL_SUBSEC_CNT_START_BIT_POS) |
                              (True << RTC_CONTROL_SEC_CNT_START_BIT_POS));

    if(RtcTimeus > RTC_SEC_TO_US) {
        /* TimeStamp is big enough to set second counter */
        Second =  ((RtcTimeus / RTC_SEC_TO_US) & RTC_SEC_MASK);
    }
    RTCREG->SECOND_COUNTER = Second;
    RtcTimeus = RtcTimeus - (Second * RTC_SEC_TO_US);
    if(RtcTimeus > False) {
        /* Convert TimeStamp to sub_seconds */
        SubSecond =  (uint16_t)((float)(RtcTimeus * RTC_CLOCK_HZ / RTC_SEC_TO_US)) & RTC_SUB_SEC_MASK;
    }
    /* Set SUB_SEC_ALARM */
    RTCREG->SUB_SECOND_COUNTER = SubSecond;

    while(RTCREG->STATUS.BITS.BSY_CTRL_REG_WRT == True); /* Wait for RTC to finish writing register - RTC operates on 32K clock as compared to 32M core*/
    /* Start RTC */
    RTCREG->CONTROL.WORD |= ((True << RTC_CONTROL_SUBSEC_CNT_START_BIT_POS) |
                             (True << RTC_CONTROL_SEC_CNT_START_BIT_POS));

    while(RTCREG->STATUS.BITS.BSY_ANY_WRT == True); /* Wait for RTC to finish writing register - RTC operates on 32K clock as compared to 32M core*/
}

/* See rtc.h for details */
void fRtcHandler(void)
{
    /* Disable RTC interrupt */
    NVIC_DisableIRQ(Rtc_IRQn);

    /* Clear sec & sub_sec interrupts */
    RTCREG->INT_CLEAR.WORD = (
    	(True << RTC_INT_CLR_SUB_SEC_BIT_POS) |
        (True << RTC_INT_CLR_SEC_BIT_POS)
	);

    /* Disable sub seconds and seconds interrupts */
    RTCREG->CONTROL.WORD &= ~(
    	(True << RTC_CONTROL_SUBSEC_CNT_INT_BIT_POS) |
        (True << RTC_CONTROL_SEC_CNT_INT_BIT_POS)
	);

	NVIC_EnableIRQ(Rtc_IRQn);
	
    /* Wait for RTC to finish writing registers */
    while(RTCREG->STATUS.WORD &
    	(
    		(True << RTC_STATUS_CONTROL_WRT_BIT_POS) |
			(True << RTC_STATUS_SUB_SEC_INT_CLR_WRT_BIT_POS) |
            (True << RTC_STATUS_SEC_INT_CLR_WRT_BIT_POS)
		)
	);
	
	lp_ticker_irq_handler();
}

boolean fIsRtcEnabled(void)
{
    if(RTCREG->CONTROL.BITS.SUB_SEC_COUNTER_EN | RTCREG->CONTROL.BITS.SEC_COUNTER_EN) {
        return True;
    } else {
        return False;
    }
}