File content as of revision 627:4fa1328d9c60:

/***************************************************************************//**
 * @file us_ticker.c
 *******************************************************************************
 * @section License
 * <b>(C) Copyright 2015 Silicon Labs, http://www.silabs.com</b>
 *******************************************************************************
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 *
 * DISCLAIMER OF WARRANTY/LIMITATION OF REMEDIES: Silicon Labs has no
 * obligation to support this Software. Silicon Labs is providing the
 * Software "AS IS", with no express or implied warranties of any kind,
 * including, but not limited to, any implied warranties of merchantability
 * or fitness for any particular purpose or warranties against infringement
 * of any proprietary rights of a third party.
 *
 * Silicon Labs will not be liable for any consequential, incidental, or
 * special damages, or any other relief, or for any claim by any third party,
 * arising from your use of this Software.
 *
 ******************************************************************************/

#include <stddef.h>
#include "us_ticker_api.h"
#include "cmsis.h"
#include "mbed_assert.h"
#include "em_cmu.h"
#include "em_timer.h"
#include "device_peripherals.h"
#include "device.h"
#include "clocking.h"
#include "sleep_api.h"
#include "sleepmodes.h"

#define TIMER_LEAST_ACTIVE_SLEEPMODE EM1
/**
 * Timer functions for microsecond ticker.
 * mbed expects a 32-bit timer. Since the EFM32 only has 16-bit timers,
 * the upper 16 bits are implemented in software.
 */

static uint8_t us_ticker_inited = 0;    // Is ticker initialized yet

static volatile uint32_t ticker_cnt = 0x2ff00;  //Internal overflow count, used to extend internal 16-bit counter to (MHz * 32-bit)
static volatile uint16_t ticker_int_rem = 0;    //Timer match value for user interrupt
static volatile uint32_t ticker_int_cnt = 0;    //Amount of overflows until user interrupt
static volatile uint8_t  ticker_freq_mhz = 0;   //Frequency of timer in MHz

void us_ticker_irq_handler_internal(void)
{
    /* Check for user interrupt expiration */
    if (TIMER_IntGet(US_TICKER_TIMER) & TIMER_IF_CC0) {
        if (ticker_int_rem > 0) {
            TIMER_CompareSet(US_TICKER_TIMER, 0, ticker_int_rem);
            ticker_int_rem = 0;
            TIMER_IntClear(US_TICKER_TIMER, TIMER_IF_CC0);
        } else if (ticker_int_cnt > 0) {
            ticker_int_cnt--;
            TIMER_IntClear(US_TICKER_TIMER, TIMER_IF_CC0);
        } else {
            us_ticker_irq_handler();
        }
    }

    /* Handle timer overflow */
    if (TIMER_IntGet(US_TICKER_TIMER) & TIMER_IF_OF) {
        ticker_cnt++;
        if(ticker_cnt >= (((uint32_t)ticker_freq_mhz) << 16)) ticker_cnt = 0;
        TIMER_IntClear(US_TICKER_TIMER, TIMER_IF_OF);
    }
}

void us_ticker_init(void)
{
    if (us_ticker_inited) {
        return;
    }
    us_ticker_inited = 1;

    /* Enable clock for TIMERs */
    CMU_ClockEnable(US_TICKER_TIMER_CLOCK, true);

    /* Clear TIMER counter value */
    TIMER_CounterSet(US_TICKER_TIMER, 0);

    /* Get frequency of clock in MHz for scaling ticks to microseconds */
    ticker_freq_mhz = (REFERENCE_FREQUENCY / 1000000);
    MBED_ASSERT(ticker_freq_mhz > 0);

    /*
     * Calculate maximum prescaler that gives at least 1 MHz frequency, while keeping clock as an integer multiple of 1 MHz.
     * Example: 14 MHz => prescaler = 1 (i.e. DIV2), ticker_freq_mhz = 7;
     *          24 MHz => prescaler = 3 (i.e. DIV8), ticker_freq_mhz = 3;
     *          48 MHz => prescaler = 4 (i.e. DIV16), ticker_freq_mhz = 3;
     * Limit prescaling to maximum prescaler value, which is 10 (DIV1024).
     */
    uint32_t prescaler = 0;
    while((ticker_freq_mhz & 1) == 0 && prescaler <= 10) {
        ticker_freq_mhz = ticker_freq_mhz >> 1;
        prescaler++;
    }

    /* Set prescaler */
    US_TICKER_TIMER->CTRL = (US_TICKER_TIMER->CTRL & ~_TIMER_CTRL_PRESC_MASK) | (prescaler << _TIMER_CTRL_PRESC_SHIFT);

    /* Select Compare Channel parameters */
    TIMER_InitCC_TypeDef timerCCInit = TIMER_INITCC_DEFAULT;
    timerCCInit.mode = timerCCModeCompare;

    /* Configure Compare Channel 0 */
    TIMER_InitCC(US_TICKER_TIMER, 0, &timerCCInit);

    /* Enable interrupt vector in NVIC */
    TIMER_IntEnable(US_TICKER_TIMER, TIMER_IEN_OF);
    NVIC_SetVector(US_TICKER_TIMER_IRQ, (uint32_t) us_ticker_irq_handler_internal);
    NVIC_EnableIRQ(US_TICKER_TIMER_IRQ);

    /* Set top value */
    TIMER_TopSet(US_TICKER_TIMER, 0xFFFF);

    /* Start TIMER */
    TIMER_Enable(US_TICKER_TIMER, true);
}

uint32_t us_ticker_read()
{
    uint32_t volatile countH_old, countH, countL;

    if (!us_ticker_inited) {
        us_ticker_init();
    }

    /* Avoid jumping in time by reading high bits twice */
    do {
        countH_old = ticker_cnt;
        /* If the counter overflowed while in the IRQ handler for the CC0 interrupt,
         * it hasn't had time to update ticker_cnt yet. Take this into account here. */
        if (TIMER_IntGet(US_TICKER_TIMER) & TIMER_IF_OF) {
            countH_old += 1;
        }
        countL = US_TICKER_TIMER->CNT;
        countH = ticker_cnt;
        /* If the counter overflowed while in the IRQ handler for the CC0 interrupt,
         * it hasn't had time to update ticker_cnt yet. Take this into account here. */
        if (TIMER_IntGet(US_TICKER_TIMER) & TIMER_IF_OF) {
            countH += 1;
        }
    } while (countH_old != countH);

    /* Merge upper (mhz * 16-bit) and lower 16-bit into 64bit */
    uint64_t count = ((uint64_t)countH << 16) | (uint64_t)countL;
    /* Divide by ticker_freq_mhz to get 32-bit 1MHz timestamp */
    return (count / ticker_freq_mhz);
}

void us_ticker_set_interrupt(timestamp_t timestamp)
{
    int32_t delta = 0, ts = timestamp, time = us_ticker_read();

    if((US_TICKER_TIMER->IEN & TIMER_IEN_CC0) == 0) {
        //Timer was disabled, but is going to be enabled. Set sleep mode.
        blockSleepMode(TIMER_LEAST_ACTIVE_SLEEPMODE);
    }
    TIMER_IntDisable(US_TICKER_TIMER, TIMER_IEN_CC0);

    delta = ts - time;
    if(delta <= ticker_freq_mhz) {
        delta = ticker_freq_mhz;
        timestamp = us_ticker_read() + 0x100;
    }

    /* Multiply by ticker_freq_mhz to get clock ticks */
    delta *= ticker_freq_mhz;
    /* Overflowing this doesn't matter, since we only need the lower 16 bits */
    ts *= ticker_freq_mhz;

    /* Split delta between timers */
    ticker_int_cnt = (((uint64_t)delta) >> 16) & 0xFFFFFFFF;
    ticker_int_rem = ts & 0xFFFF;

    /* Set compare channel 0 to (current position + lower 16 bits of delta).
     * If lower 16 bits is a small number, we a do one compare of (current + lower 16 + 0x8000)
     * and then one of (current + lower 16). Else, we simply use (current + lower 16).
     *
     * When time from lower 16 bits have elapsed, run complete cycles with ticker_int_rem as
     * reference ticker_int_cnt times. */
    if ((delta & 0xFFFF) < 0x8000 && ticker_int_cnt > 0) {
        TIMER_CompareSet(US_TICKER_TIMER, 0, ticker_int_rem + 0x8000);
        ticker_int_cnt--;
    } else {
        TIMER_CompareSet(US_TICKER_TIMER, 0, ticker_int_rem);
        ticker_int_rem = 0;
    }
    TIMER_IntClear(US_TICKER_TIMER, TIMER_IFC_CC0);
    TIMER_IntEnable(US_TICKER_TIMER, TIMER_IEN_CC0);
}

void us_ticker_disable_interrupt(void)
{
    if((US_TICKER_TIMER->IEN & TIMER_IEN_CC0) != 0) {
        //Timer was enabled, but is going to get disabled. Clear sleepmode.
        unblockSleepMode(TIMER_LEAST_ACTIVE_SLEEPMODE);
    }
    /* Disable compare channel interrupts */
    TIMER_IntDisable(US_TICKER_TIMER, TIMER_IEN_CC0);
}

void us_ticker_clear_interrupt(void)
{
    /* Clear compare channel interrupts */
    TIMER_IntClear(US_TICKER_TIMER, TIMER_IFC_CC0);
}