/*
   * Copyright (C) 2014 Freie Universität Berlin, Hinnerk van Bruinehsen
   *
   * This file is subject to the terms and conditions of the GNU Lesser
   * General Public License v2.1. See the file LICENSE in the top level
   * directory for more details.
   */
  
  /**
   * @ingroup     driver_periph
   * @{
   *
   * @file
   * @brief       Low-level timer driver implementation for the ATmega family
   *
   * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
   * @author      Hinnerk van Bruinehsen <h.v.bruinehsen@fu-berlin.de>
   *
   * @}
   */
  
  #include <avr/interrupt.h>
  
  #include "board.h"
  #include "cpu.h"
  #include "thread.h"
  
  #include "periph/timer.h"
  #include "periph_conf.h"
  
  #define ENABLE_DEBUG    (0)
  #include "debug.h"
  
  /**
   * @brief   All timers have three channels
   */
  #define CHANNELS                (3)
  
  /**
   * @brief   We have 5 possible prescaler values
   */
  #define PRESCALE_NUMOF          (5U)
  
  /**
   * @brief   Possible prescaler values, encoded as 2 ^ val
   */
  static const uint8_t prescalers[] = { 0, 3, 6, 8, 10 };
  
  /**
   * @brief   Timer state context
   */
  typedef struct {
      mega_timer_t *dev;          /**< timer device */
      volatile uint8_t *mask;     /**< address of interrupt mask register */
      volatile uint8_t *flag;     /**< address of interrupt flag register */
      timer_cb_t cb;              /**< interrupt callback */
      void *arg;                  /**< interrupt callback argument */
      uint8_t mode;               /**< remember the configured mode */
      uint8_t isrs;               /**< remember the interrupt state */
  } ctx_t;
  
  /**
   * @brief   Allocate memory for saving the device states
   * @{
   */
  #ifdef TIMER_NUMOF
  static ctx_t ctx[] = {
  #ifdef TIMER_0
      { TIMER_0, TIMER_0_MASK, TIMER_0_FLAG, NULL, NULL, 0, 0 },
  #endif
  #ifdef TIMER_1
      { TIMER_1, TIMER_1_MASK, TIMER_1_FLAG, NULL, NULL, 0, 0 },
  #endif
  #ifdef TIMER_2
      { TIMER_2, TIMER_2_MASK, TIMER_2_FLAG, NULL, NULL, 0, 0 },
  #endif
  #ifdef TIMER_3
      { TIMER_3, TIMER_3_MASK, TIMER_3_FLAG, NULL, NULL, 0, 0 },
  #endif
  };
  #else
  /* fallback if no timer is configured */
  static ctx_t *ctx[] = {{ NULL }};
  #endif
  /** @} */
  
  /**
   * @brief Setup the given timer
   */
  int timer_init(tim_t tim, unsigned long freq, timer_cb_t cb, void *arg)
  {
      DEBUG("timer.c: freq = %ld\n", freq);
      uint8_t pre = 0;
  
      /* make sure given device is valid */
      if (tim >= TIMER_NUMOF) {
          return -1;
      }
  
      /* figure out if freq is applicable */
      for (; pre < PRESCALE_NUMOF; pre++) {
          if ((CLOCK_CORECLOCK >> prescalers[pre]) == freq) {
              break;
          }
      }
      if (pre == PRESCALE_NUMOF) {
          DEBUG("timer.c: prescaling failed!\n");
          return -1;
      }
  
      /* stop and reset timer */
      ctx[tim].dev->CRA = 0;
      ctx[tim].dev->CRB = 0;
      ctx[tim].dev->CRC = 0;
      ctx[tim].dev->CNT = 0;
  
      /* save interrupt context and timer mode */
      ctx[tim].cb   = cb;
      ctx[tim].arg  = arg;
      ctx[tim].mode = (pre + 1);
  
      /* enable timer with calculated prescaler */
      ctx[tim].dev->CRB = (pre + 1);
      DEBUG("timer.c: prescaler set at %d\n", pre + 1);
  
      return 0;
  }
  
  int timer_set(tim_t tim, int channel, unsigned int timeout)
  {
      return timer_set_absolute(tim, channel, timer_read(tim) + timeout);
  }
  
  int timer_set_absolute(tim_t tim, int channel, unsigned int value)
  {
      if (channel >= CHANNELS) {
          return -1;
      }
  
      ctx[tim].dev->OCR[channel] = (uint16_t)value;
      *ctx[tim].flag &= ~(1 << (channel + OCF1A));
      *ctx[tim].mask |=  (1 << (channel + OCIE1A));
  
      return 1;
  }
  
  int timer_clear(tim_t tim, int channel)
  {
      if (channel >= CHANNELS) {
          return -1;
      }
  
      *ctx[tim].mask &= ~(1 << (channel + OCIE1A));
  
      return 0;
  }
  
  unsigned int timer_read(tim_t tim)
  {
      return (unsigned int)ctx[tim].dev->CNT;
  }
  
  void timer_stop(tim_t tim)
  {
      ctx[tim].dev->CRB = 0;
  }
  
  void timer_start(tim_t tim)
  {
      ctx[tim].dev->CRB = ctx[tim].mode;
  }
  
  void timer_irq_enable(tim_t tim)
  {
      *ctx[tim].mask = ctx[tim].isrs;
  }
  
  void timer_irq_disable(tim_t tim)
  {
      ctx[tim].isrs = *(ctx[tim].mask);
      *ctx[tim].mask = 0;
  }
  
  #ifdef TIMER_NUMOF
  static inline void _isr(tim_t tim, int chan)
  {
      __enter_isr();
  
      *ctx[tim].mask &= ~(1 << (chan + OCIE1A));
      ctx[tim].cb(ctx[tim].arg, chan);
  
      if (sched_context_switch_request) {
          thread_yield();
      }
  
      __exit_isr();
  }
  #endif
  
  #ifdef TIMER_0
  ISR(TIMER_0_ISRA, ISR_BLOCK)
  {
      _isr(0, 0);
  }
  
  ISR(TIMER_0_ISRB, ISR_BLOCK)
  {
      _isr(0, 1);
  }
  
  #ifdef TIMER_0_ISRC
  ISR(TIMER_0_ISRC, ISR_BLOCK)
  {
      _isr(0, 2);
  }
  #endif /* TIMER_0_ISRC */
  #endif /* TIMER_0 */
  
  #ifdef TIMER_1
  ISR(TIMER_1_ISRA, ISR_BLOCK)
  {
      _isr(1, 0);
  }
  
  ISR(TIMER_1_ISRB, ISR_BLOCK)
  {
      _isr(1, 1);
  }
  
  ISR(TIMER_1_ISRC, ISR_BLOCK)
  {
      _isr(1, 2);
  }
  #endif /* TIMER_1 */
  
  #ifdef TIMER_2
  ISR(TIMER_2_ISRA, ISR_BLOCK)
  {
      _isr(2, 0);
  }
  
  ISR(TIMER_2_ISRB, ISR_BLOCK)
  {
      _isr(2, 1);
  }
  
  ISR(TIMER_2_ISRC, ISR_BLOCK)
  {
      _isr(2, 2);
  }
  #endif /* TIMER_2 */
  
  #ifdef TIMER_3
  ISR(TIMER_3_ISRA, ISR_BLOCK)
  {
      _isr(2, 0);
  }
  
  ISR(TIMER_3_ISRB, ISR_BLOCK)
  {
      _isr(2, 1);
  }
  
  ISR(TIMER_3_ISRC, ISR_BLOCK)
  {
      _isr(2, 2);
  }
  #endif /* TIMER_3 */