text: /* mbed Microcontroller Library
   * Copyright (c) 2015-2016 Nuvoton
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
   
  #include "lp_ticker_api.h"
  
  #if DEVICE_LOWPOWERTIMER
  
  #include "sleep_api.h"
  #include "nu_modutil.h"
  #include "nu_miscutil.h"
  #include "mbed_critical.h"
  
  // lp_ticker tick = us = timestamp
  #define US_PER_TICK             (1)
  #define US_PER_SEC              (1000 * 1000)
  
  #define US_PER_TMR2_INT         (US_PER_SEC * 10)
  #define TMR2_CLK_PER_SEC        (__LXT)
  #define TMR2_CLK_PER_TMR2_INT   ((uint32_t) ((uint64_t) US_PER_TMR2_INT * TMR2_CLK_PER_SEC / US_PER_SEC))
  #define TMR3_CLK_PER_SEC        (__LXT)
  
  static void tmr2_vec(void);
  static void tmr3_vec(void);
  static void lp_ticker_arm_cd(void);
  
  static int lp_ticker_inited = 0;
  static volatile uint32_t counter_major = 0;
  static volatile uint32_t cd_major_minor_clks = 0;
  static volatile uint32_t cd_minor_clks = 0;
  static volatile uint32_t wakeup_tick = (uint32_t) -1;
  
  // NOTE: To wake the system from power down mode, timer clock source must be ether LXT or LIRC.
  // NOTE: TIMER_2 for normal counting and TIMER_3 for scheduled wakeup
  static const struct nu_modinit_s timer2_modinit = {TIMER_2, TMR2_MODULE, CLK_CLKSEL1_TMR2SEL_LXT, 0, TMR2_RST, TMR2_IRQn, (void *) tmr2_vec};
  static const struct nu_modinit_s timer3_modinit = {TIMER_3, TMR3_MODULE, CLK_CLKSEL1_TMR3SEL_LXT, 0, TMR3_RST, TMR3_IRQn, (void *) tmr3_vec};
  
  #define TMR_CMP_MIN         2
  #define TMR_CMP_MAX         0xFFFFFFu
  
  void lp_ticker_init(void)
  {
      if (lp_ticker_inited) {
          return;
      }
      lp_ticker_inited = 1;
      
      counter_major = 0;
      cd_major_minor_clks = 0;
      cd_minor_clks = 0;
      wakeup_tick = (uint32_t) -1;
  
      // Reset module
      SYS_ResetModule(timer2_modinit.rsetidx);
      SYS_ResetModule(timer3_modinit.rsetidx);
      
      // Select IP clock source
      CLK_SetModuleClock(timer2_modinit.clkidx, timer2_modinit.clksrc, timer2_modinit.clkdiv);
      CLK_SetModuleClock(timer3_modinit.clkidx, timer3_modinit.clksrc, timer3_modinit.clkdiv);
      // Enable IP clock
      CLK_EnableModuleClock(timer2_modinit.clkidx);
      CLK_EnableModuleClock(timer3_modinit.clkidx);
  
      // Configure clock
      uint32_t clk_timer2 = TIMER_GetModuleClock((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      uint32_t prescale_timer2 = clk_timer2 / TMR2_CLK_PER_SEC - 1;
      MBED_ASSERT((prescale_timer2 != (uint32_t) -1) && prescale_timer2 <= 127);
      MBED_ASSERT((clk_timer2 % TMR2_CLK_PER_SEC) == 0);
      uint32_t cmp_timer2 = TMR2_CLK_PER_TMR2_INT;
      MBED_ASSERT(cmp_timer2 >= TMR_CMP_MIN && cmp_timer2 <= TMR_CMP_MAX);
      // Continuous mode
      // NOTE: TIMER_CTL_CNTDATEN_Msk exists in NUC472, but not in M451. In M451, TIMER_CNT is updated continuously by default.
      ((TIMER_T *) NU_MODBASE(timer2_modinit.modname))->CTL = TIMER_PERIODIC_MODE | prescale_timer2/* | TIMER_CTL_CNTDATEN_Msk*/;
      ((TIMER_T *) NU_MODBASE(timer2_modinit.modname))->CMP = cmp_timer2;
      
      // Set vector
      NVIC_SetVector(timer2_modinit.irq_n, (uint32_t) timer2_modinit.var);
      NVIC_SetVector(timer3_modinit.irq_n, (uint32_t) timer3_modinit.var);
      
      NVIC_EnableIRQ(timer2_modinit.irq_n);
      NVIC_EnableIRQ(timer3_modinit.irq_n);
      
      TIMER_EnableInt((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      TIMER_EnableWakeup((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      
      // NOTE: TIMER_Start() first and then lp_ticker_set_interrupt(); otherwise, we may get stuck in lp_ticker_read() because
      //       timer is not running.
      
      // Start timer
      TIMER_Start((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      
      // Schedule wakeup to match semantics of lp_ticker_get_compare_match()
      lp_ticker_set_interrupt(wakeup_tick);
  }
  
  timestamp_t lp_ticker_read()
  {    
      if (! lp_ticker_inited) {
          lp_ticker_init();
      }
      
      TIMER_T * timer2_base = (TIMER_T *) NU_MODBASE(timer2_modinit.modname);
      
      do {
          uint64_t major_minor_clks;
          uint32_t minor_clks;
          
          // NOTE: As TIMER_CNT = TIMER_CMP and counter_major has increased by one, TIMER_CNT doesn't change to 0 for one tick time.
          // NOTE: As TIMER_CNT = TIMER_CMP or TIMER_CNT = 0, counter_major (ISR) may not sync with TIMER_CNT. So skip and fetch stable one at the cost of 1 clock delay on this read.
          do {
              core_util_critical_section_enter();
          
              // NOTE: Order of reading minor_us/carry here is significant.
              minor_clks = TIMER_GetCounter(timer2_base);
              uint32_t carry = (timer2_base->INTSTS & TIMER_INTSTS_TIF_Msk) ? 1 : 0;
              // When TIMER_CNT approaches TIMER_CMP and will wrap soon, we may get carry but TIMER_CNT not wrapped. Hanlde carefully carry == 1 && TIMER_CNT is near TIMER_CMP.
              if (carry && minor_clks > (TMR2_CLK_PER_TMR2_INT / 2)) {
                  major_minor_clks = (counter_major + 1) * TMR2_CLK_PER_TMR2_INT;
              }
              else {
                  major_minor_clks = (counter_major + carry) * TMR2_CLK_PER_TMR2_INT + minor_clks;
              }
              
              core_util_critical_section_exit();
          }
          while (minor_clks == 0 || minor_clks == TMR2_CLK_PER_TMR2_INT);
  
          // Add power-down compensation
          return ((uint64_t) major_minor_clks * US_PER_SEC / TMR3_CLK_PER_SEC / US_PER_TICK);
      }
      while (0);
  }
  
  void lp_ticker_set_interrupt(timestamp_t timestamp)
  {
      uint32_t now = lp_ticker_read();
      wakeup_tick = timestamp;
      
      TIMER_Stop((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
      
      /**
       * FIXME: Scheduled alarm may go off incorrectly due to wrap around.
       * Conditions in which delta is negative:
       * 1. Wrap around
       * 2. Newly scheduled alarm is behind now
       */ 
      //int delta = (timestamp > now) ? (timestamp - now) : (uint32_t) ((uint64_t) timestamp + 0xFFFFFFFFu - now);
      int delta = (int) (timestamp - now);
      if (delta > 0) {
          cd_major_minor_clks = (uint64_t) delta * US_PER_TICK * TMR3_CLK_PER_SEC / US_PER_SEC;
          lp_ticker_arm_cd();
      }
      else {
          cd_major_minor_clks = cd_minor_clks = 0;
          /**
           * This event was in the past. Set the interrupt as pending, but don't process it here.
           * This prevents a recurive loop under heavy load which can lead to a stack overflow.
           */  
          NVIC_SetPendingIRQ(timer3_modinit.irq_n);
      }
  }
  
  void lp_ticker_disable_interrupt(void)
  {
      TIMER_DisableInt((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
  }
  
  void lp_ticker_clear_interrupt(void)
  {
      TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
  }
  
  static void tmr2_vec(void)
  {
      TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      TIMER_ClearWakeupFlag((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
      counter_major ++;
  }
  
  static void tmr3_vec(void)
  {
      TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
      TIMER_ClearWakeupFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
      cd_major_minor_clks = (cd_major_minor_clks > cd_minor_clks) ? (cd_major_minor_clks - cd_minor_clks) : 0;
      if (cd_major_minor_clks == 0) {
          // NOTE: lp_ticker_set_interrupt() may get called in lp_ticker_irq_handler();
          lp_ticker_irq_handler();
      }
      else {
          lp_ticker_arm_cd();
      }
  }
  
  static void lp_ticker_arm_cd(void)
  {
      TIMER_T * timer3_base = (TIMER_T *) NU_MODBASE(timer3_modinit.modname);
      
      // Reset 8-bit PSC counter, 24-bit up counter value and CNTEN bit
      timer3_base->CTL |= TIMER_CTL_RSTCNT_Msk;
      // One-shot mode, Clock = 1 KHz 
      uint32_t clk_timer3 = TIMER_GetModuleClock((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
      uint32_t prescale_timer3 = clk_timer3 / TMR3_CLK_PER_SEC - 1;
      MBED_ASSERT((prescale_timer3 != (uint32_t) -1) && prescale_timer3 <= 127);
      MBED_ASSERT((clk_timer3 % TMR3_CLK_PER_SEC) == 0);
      // NOTE: TIMER_CTL_CNTDATEN_Msk exists in NUC472, but not in M451. In M451, TIMER_CNT is updated continuously by default.
      timer3_base->CTL &= ~(TIMER_CTL_OPMODE_Msk | TIMER_CTL_PSC_Msk/* | TIMER_CTL_CNTDATEN_Msk*/);
      timer3_base->CTL |= TIMER_ONESHOT_MODE | prescale_timer3/* | TIMER_CTL_CNTDATEN_Msk*/;
      
      cd_minor_clks = cd_major_minor_clks;
      cd_minor_clks = NU_CLAMP(cd_minor_clks, TMR_CMP_MIN, TMR_CMP_MAX);
      timer3_base->CMP = cd_minor_clks;
      
      TIMER_EnableInt(timer3_base);
      TIMER_EnableWakeup((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
      TIMER_Start(timer3_base);
  }
  #endif
  