text: /*******************************************************************************
   * Copyright (C) 2015 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
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   * 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
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   *******************************************************************************
   */
  
  #include "mbed_error.h"
  #include "us_ticker_api.h"
  #include "PeripheralNames.h"
  #include "tmr_regs.h"
  
  #define US_TIMER        MXC_TMR0
  #define US_TIMER_IRQn   TMR0_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 ticks_to_us(ticks)  ((ticks) / ticks_per_us);
  #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 term_cnt32 = US_TIMER->term_cnt32;
      US_TIMER->term_cnt32 = 0xFFFFFFFF;  // reset to max value to prevent further interrupts
      US_TIMER->intfl = (MXC_F_TMR_INTFL_TIMER0 | MXC_F_TMR_INTFL_TIMER1);    // clear interrupt
      NVIC_ClearPendingIRQ(US_TIMER_IRQn);
  
      inc_current_cnt(term_cnt32);
  
      if (event_passed(current_cnt + US_TIMER->count32, 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
              US_TIMER->term_cnt32 = 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 (US_TIMER->term_cnt32 < US_TIMER->count32) {
                  // the timestamp has expired
                  US_TIMER->term_cnt32 = 0xFFFFFFFF;  // reset to max value to prevent further interrupts
                  US_TIMER->intfl = (MXC_F_TMR_INTFL_TIMER0 | MXC_F_TMR_INTFL_TIMER1);    // clear interrupt
                  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
  
      if (SystemCoreClock <= 1000000) {
          error("us_ticker cannot operate at this SystemCoreClock");
          return;
      }
  
      // Configure timer for 32-bit continuous mode with /1 prescaler
      US_TIMER->ctrl = MXC_E_TMR_MODE_CONTINUOUS << MXC_F_TMR_CTRL_MODE_POS | (0 << MXC_F_TMR_CTRL_PRESCALE_POS);
      ticks_per_us = SystemCoreClock / 1000000;
  
      // Set the tick window to 10ms
      tick_win = SystemCoreClock/100;
  
      // Set timer overflow to the max
      US_TIMER->term_cnt32 = 0xFFFFFFFF;
      US_TIMER->pwm_cap32 = 0xFFFFFFFF;
      US_TIMER->count32 = 0;
  
      US_TIMER->intfl = (MXC_F_TMR_INTFL_TIMER0 | MXC_F_TMR_INTFL_TIMER1);    // clear pending interrupts
  
      NVIC_SetVector(US_TIMER_IRQn, (uint32_t)tmr_handler);
      NVIC_EnableIRQ(US_TIMER_IRQn);
  
      US_TIMER->inten |= MXC_F_TMR_INTEN_TIMER0;  // enable interrupts
      US_TIMER->ctrl |= MXC_F_TMR_CTRL_ENABLE0;   // enable timer
  }
  
  //******************************************************************************
  void us_ticker_deinit(void)
  {
      US_TIMER->ctrl = 0;     // disable timer
      US_TIMER->inten = 0;    // disable interrupts
      US_TIMER->intfl = (MXC_F_TMR_INTFL_TIMER0 | MXC_F_TMR_INTFL_TIMER1);    // clear interrupts
      us_ticker_inited = 0;
  }
  
  //******************************************************************************
  uint32_t us_ticker_read(void)
  {
      uint64_t current_cnt1, current_cnt2;
      uint32_t term_cnt, tmr_cnt;
      uint32_t intfl1, intfl2;
  
      if (!us_ticker_inited)
          us_ticker_init();
  
      // Ensure coherency between current_cnt and US_TIMER->count32
      do {
          current_cnt1 = current_cnt;
          intfl1 = US_TIMER->intfl;
          term_cnt = US_TIMER->term_cnt32;
          tmr_cnt = US_TIMER->count32;
          intfl2 = US_TIMER->intfl;
          current_cnt2 = current_cnt;
      } while ((current_cnt1 != current_cnt2) || (intfl1 != intfl2));
  
      // Account for an unserviced interrupt
      if (intfl1) {
          current_cnt1 += term_cnt;
      }
  
      current_cnt1 += tmr_cnt;
  
      return (current_cnt1 / ticks_per_us);
  }
  
  //******************************************************************************
  void us_ticker_set_interrupt(timestamp_t timestamp)
  {
      // Note: interrupts are disabled before this function is called.
  
      US_TIMER->ctrl &= ~MXC_F_TMR_CTRL_ENABLE0;  // disable timer
  
      if (US_TIMER->intfl) {
          US_TIMER->intfl = (MXC_F_TMR_INTFL_TIMER0 | MXC_F_TMR_INTFL_TIMER1);    // clear interrupt
          NVIC_ClearPendingIRQ(US_TIMER_IRQn);
          inc_current_cnt(US_TIMER->term_cnt32);
      }
  
      // add and reset the current count value
      inc_current_cnt(US_TIMER->count32);
      US_TIMER->count32 = 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
              US_TIMER->term_cnt32 = diff;
          } else {
              // the event occurs after the next overflow 
              US_TIMER->term_cnt32 = 0xFFFFFFFF;  // set to max
          }
      } else {
          // the requested timestamp occurs in the past
          // set the timer up to immediately expire
          US_TIMER->term_cnt32 = 1;
      }
      US_TIMER->ctrl |= MXC_F_TMR_CTRL_ENABLE0;   // enable timer
  }
  
  void us_ticker_fire_interrupt(void)
  {
      US_TIMER->ctrl &= ~MXC_F_TMR_CTRL_ENABLE0;  // disable timer
      US_TIMER->term_cnt32 = 1;
      US_TIMER->ctrl |= MXC_F_TMR_CTRL_ENABLE0;   // enable timer
  }
  
  //******************************************************************************
  void us_ticker_disable_interrupt(void)
  {
      // There are no more events, set timer overflow to the max
      US_TIMER->term_cnt32 = 0xFFFFFFFF;
  }
  
  //******************************************************************************
  void us_ticker_clear_interrupt(void)
  {
      // cleared in the local handler
  }
  
  //******************************************************************************
  void us_ticker_set(timestamp_t timestamp)
  {
      US_TIMER->ctrl &= ~MXC_F_TMR_CTRL_ENABLE0;  // disable timer
      current_cnt = (uint64_t)timestamp * ticks_per_us;
      US_TIMER->count32 = 0;
      US_TIMER->term_cnt32 = 0xFFFFFFFF;
      US_TIMER->ctrl |= MXC_F_TMR_CTRL_ENABLE0;   // enable 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);
      }
  }
  
  void us_ticker_free(void)
  {
  
  }
  