File content as of revision 157:ff67d9f36b67:

/*******************************************************************************
 * Copyright (c) 2016 Maxim Integrated Products, Inc., All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL MAXIM INTEGRATED BE LIABLE FOR ANY CLAIM, DAMAGES
 * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * Except as contained in this notice, the name of Maxim Integrated
 * Products, Inc. shall not be used except as stated in the Maxim Integrated
 * Products, Inc. Branding Policy.
 *
 * The mere transfer of this software does not imply any licenses
 * of trade secrets, proprietary technology, copyrights, patents,
 * trademarks, maskwork rights, or any other form of intellectual
 * property whatsoever. Maxim Integrated Products, Inc. retains all
 * ownership rights.
 *******************************************************************************
 */

#include <stddef.h>
#include "mbed_error.h"
#include "us_ticker_api.h"
#include "PeripheralNames.h"
#include "tmr.h"

#define US_TIMER        MXC_TMR0
#define US_TIMER_IRQn   TMR0_0_IRQn

static int us_ticker_inited = 0;
static uint32_t ticks_per_us;
static uint32_t tick_win;
static volatile uint64_t current_cnt;   // Hold the current ticks
static volatile uint64_t event_cnt;     // Holds the value of the next event

#define MAX_TICK_VAL    ((uint64_t)0xFFFFFFFF * ticks_per_us)

//******************************************************************************
static inline void inc_current_cnt(uint32_t inc)
{
    // Overflow the ticker when the us ticker overflows
    current_cnt += inc;
    if (current_cnt > MAX_TICK_VAL) {
        current_cnt -= (MAX_TICK_VAL + 1);
    }
}

//******************************************************************************
static inline int event_passed(uint64_t current, uint64_t event)
{
    // Determine if the event has already happened.
    // If the event is behind the current ticker, within a window,
    // then the event has already happened.
    if (((current < tick_win) && ((event < current) ||
                                  (event > (MAX_TICK_VAL - (tick_win - current))))) ||
            ((event < current) && (event > (current - tick_win)))) {
        return 1;
    }

    return 0;
}

//******************************************************************************
static inline uint64_t event_diff(uint64_t current, uint64_t event)
{
    // Check to see if the ticker will overflow before the event
    if(current <= event) {
        return (event - current);
    }

    return ((MAX_TICK_VAL - current) + event);
}

//******************************************************************************
static void tmr_handler(void)
{
    uint32_t cmp = TMR32_GetCompare(US_TIMER);
    TMR32_SetCompare(US_TIMER, 0xFFFFFFFF); // reset to max value to prevent further interrupts
    TMR32_ClearFlag(US_TIMER);
    NVIC_ClearPendingIRQ(US_TIMER_IRQn);

    inc_current_cnt(cmp);

    if (event_passed(current_cnt + TMR32_GetCount(US_TIMER), event_cnt)) {
        // the timestamp has expired
        event_cnt = 0xFFFFFFFFFFFFFFFFULL;  // reset to max value
        us_ticker_irq_handler();
    } else {
        uint64_t diff = event_diff(current_cnt, event_cnt);
        if (diff < (uint64_t)0xFFFFFFFF) {
            // the event occurs before the next overflow
            TMR32_SetCompare(US_TIMER, diff);

            // Since the timer keeps counting after the terminal value is reached, it is possible that the new
            // terminal value is in the past.
            if (TMR32_GetCompare(US_TIMER) < TMR32_GetCount(US_TIMER)) {
                // the timestamp has expired
                TMR32_SetCompare(US_TIMER, 0xFFFFFFFF); // reset to max value to prevent further interrupts
                TMR32_ClearFlag(US_TIMER);
                NVIC_ClearPendingIRQ(US_TIMER_IRQn);
                event_cnt = 0xFFFFFFFFFFFFFFFFULL;  // reset to max value
                us_ticker_irq_handler();
            }
        }
    }
}

//******************************************************************************
void us_ticker_init(void)
{
    if (us_ticker_inited) {
        return;
    }

    us_ticker_inited = 1;
    current_cnt = 0;
    event_cnt = 0xFFFFFFFFFFFFFFFFULL;          // reset to max value
    ticks_per_us = SystemCoreClock / 1000000;
    tick_win = SystemCoreClock / 100;           // Set the tick window to 10ms

    int retval = TMR_Init(US_TIMER, TMR_PRESCALE_DIV_2_0, NULL);
    MBED_ASSERT(retval == E_NO_ERROR);

    tmr32_cfg_t cfg;
    cfg.mode = TMR32_MODE_CONTINUOUS;
    cfg.polarity = TMR_POLARITY_UNUSED;
    cfg.compareCount = 0xFFFFFFFF;
    TMR32_Config(US_TIMER, &cfg);

    NVIC_SetVector(US_TIMER_IRQn, tmr_handler);
    NVIC_EnableIRQ(US_TIMER_IRQn);
    TMR32_EnableINT(US_TIMER);

    TMR32_Start(US_TIMER);
}

//******************************************************************************
void us_ticker_deinit(void)
{
    TMR32_Stop(US_TIMER);
    TMR32_DisableINT(US_TIMER);
    TMR32_ClearFlag(US_TIMER);
    us_ticker_inited = 0;
}

//******************************************************************************
uint32_t us_ticker_read(void)
{
    uint64_t current_cnt1, current_cnt2;
    uint32_t cmp, cnt;
    uint32_t flag1, flag2;

    if (!us_ticker_inited) {
        us_ticker_init();
    }

    // Ensure coherency between current_cnt and TMR32_GetCount()
    do {
        current_cnt1 = current_cnt;
        flag1 = TMR32_GetFlag(US_TIMER);
        cmp = TMR32_GetCompare(US_TIMER);
        cnt = TMR32_GetCount(US_TIMER);
        flag2 = TMR32_GetFlag(US_TIMER);
        current_cnt2 = current_cnt;
    } while ((current_cnt1 != current_cnt2) || (flag1 != flag2));

    // Account for an unserviced interrupt
    if (flag1) {
        current_cnt1 += cmp;
    }

    current_cnt1 += cnt;

    return (current_cnt1 / ticks_per_us);
}

//******************************************************************************
void us_ticker_set_interrupt(timestamp_t timestamp)
{
    // Note: interrupts are disabled before this function is called.

    TMR32_Stop(US_TIMER);

    if (TMR32_GetFlag(US_TIMER)) {
        TMR32_ClearFlag(US_TIMER);
        NVIC_ClearPendingIRQ(US_TIMER_IRQn);
        inc_current_cnt(TMR32_GetCompare(US_TIMER));
    }

    // add and reset the current count value
    inc_current_cnt(TMR32_GetCount(US_TIMER));
    TMR32_SetCount(US_TIMER, 0);

    // add the number of cycles that the timer is disabled here for
    inc_current_cnt(200);

    event_cnt = (uint64_t)timestamp * ticks_per_us;

    // Check to see if the event has already passed
    if (!event_passed(current_cnt, event_cnt)) {
        uint64_t diff = event_diff(current_cnt, event_cnt);
        if (diff < (uint64_t)0xFFFFFFFF) {
            // the event occurs before the next overflow
            TMR32_SetCompare(US_TIMER, diff);
        } else {
            // the event occurs after the next overflow
            TMR32_SetCompare(US_TIMER, 0xFFFFFFFF);  // set to max
        }
    } else {
        // the requested timestamp occurs in the past
        // set the timer up to immediately expire
        TMR32_SetCompare(US_TIMER, 1);
    }

    TMR32_Start(US_TIMER);
}

//******************************************************************************
void us_ticker_disable_interrupt(void)
{
    // There are no more events, set timer overflow to the max
    TMR32_SetCompare(US_TIMER, 0xFFFFFFFF);
}

//******************************************************************************
void us_ticker_clear_interrupt(void)
{
    // cleared in the local handler
}

//******************************************************************************
void us_ticker_set(timestamp_t timestamp)
{
    TMR32_Stop(US_TIMER);
    current_cnt = (uint64_t)timestamp * ticks_per_us;
    TMR32_SetCount(US_TIMER, 0);
    TMR32_SetCompare(US_TIMER, 0xFFFFFFFF);
    TMR32_Start(US_TIMER);

    if (((uint64_t)timestamp * ticks_per_us) >= event_cnt) {
        // The next timestamp has elapsed. Trigger the interrupt to handle it.
        NVIC_SetPendingIRQ(US_TIMER_IRQn);
    }
}