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/**
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 * Copyright (c) 2007 Colony Project
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 * 
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 * Permission is hereby granted, free of charge, to any person
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 * obtaining a copy of this software and associated documentation
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 * files (the "Software"), to deal in the Software without
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 * restriction, including without limitation the rights to use,
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 * copy, modify, merge, publish, distribute, sublicense, and/or sell
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 * copies of the Software, and to permit persons to whom the
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 * Software is furnished to do so, subject to the following
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 * conditions:
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 * 
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 * The above copyright notice and this permission notice shall be
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 * included in all copies or substantial portions of the Software.
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 * 
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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 * OTHER DEALINGS IN THE SOFTWARE.
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 **/
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/**
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 * @file time.c
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 * @brief Timer code
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 *
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 * Implementation of functions for timers.
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 *
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 * @author Colony Project, CMU Robotics Club
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 **/
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/*
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  time.c
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  anything that requires a delay
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  mostly delay_ms
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  author: Robotics Club, Colony Project
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  Change Log:
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  2.5.07 - Kevin
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  Aaron fixed the orb/servo code and made them use timer3 but compare registers B and C. He hard set the prescaler
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  to 8 so the RTC broke. Changed it so that we use a 8 prescaler which sets the compare match at 1/16th of a second.
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  You now count how many 16ths of a second you want until you trigger your actual interrupt. Works. Changed defines
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  for time so you can still call rtc_init with a scale but now it is defined in terms of actual time like second, quarter_second
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  etc. Read that section in the time.h file for more information. Tested and works, though the clock drifts more than
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  it used to
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  1.30.07 - Kevin
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  Modified the clock to run on timer3 on the Dragonfly. Works with decent accuracy. Using a prescaler of 256
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  the timer counts up to a precomputer value which will trigger an interrupt and reset the timer. Multiples of
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  256 change it by that multiple. Refer to the time.h file for all possible prescalers.
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  The interrupt will call a specified function _rtc_func every pulse.
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  All of it has been tested and it works.
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*/
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#include <avr/interrupt.h>
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#include <util/delay.h>
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#include "time.h"
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/* Calculate how many cycles to delay for to get 1 ms. Based on F_CPU which should be defined by the makefile */
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#ifdef F_CPU
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#define WAIT_CYCLES ((F_CPU / 1000) / 10)
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#else
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#define WAIT_CYCLES (8000 / 10)
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#endif
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static volatile int _rtc_val = 0;
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static volatile int _rtc_pulse = 0;
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static volatile int _rtc_scale = 32;        //Defaults to 1 Second per pulse
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static void (*_rtc_f)(void) = 0;
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/**
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 * @defgroup time Time
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 * @brief Time functions
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 * 
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 * Functions dealing with time.
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 * 
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 * @{
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 **/
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/**
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 * Delays for the specified number of milliseconds.
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 * It depends on F_CPU to be defined in order to calculate how many cycles
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 * it should delay. If it is not defined, a default clock of 8MHz is assumed.
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 * 
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 * We use _delay_loop_2 which will run assembly instructions that should be
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 * 4 cycles long. Optimizations must be enabled for this to be true.
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 * That function is called to ensure around 1ms per execution. To generate
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 * multiple ms we run a for loop of how many milliseconds are desired.
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 *
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 * The error should be just the skew on the oscillator as the formula to 
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 * calculate delay cycles should always be a whole number. The is some skew
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 * in practice though it is unavoidable. Delaying for less than 1s should make
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 * the error negligable.
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 *
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 * @param ms the number of milliseconds to delay for
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 **/
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void delay_ms(int ms) {
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    for (; ms > 0; ms--) {
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        _delay_loop_2(WAIT_CYCLES);
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    }
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}
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/*         Prescales defined in time.h. SECOND will give you 1 second.
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        More scales are defined in the time.h file.
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        rtc_func is the address to a function that you want called every clock tick. */
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/**
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 * Initializes the real time clock. Prescales are defined in time.h.
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 * For example, SECOND will give 1 second. The specified function is
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 * called every clock tick. For the real time clock to activate,
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 * interrupts must be enabled. (through sei() )
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 *
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 * @param prescale_opt the period with which the timer is triggered
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 * @param rtc_func the function called when the timer is triggered
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 *
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 * @see rtc_get, rtc_reset
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 *
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 **/
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void rtc_init(int prescale_opt, void (*rtc_func)(void)) {
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  //Clear timer register for Timer 3
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  TCNT3 = 0;
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  /*         This sets the Waveform Generation Module to CTC (Clear Timer on Compare) Mode (100)
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        See page135 in Atmega128 Docs for more modes and explanations */
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  TCCR3B |= _BV(WGM32);
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  /*         This sets the prescaler for the system clock (8MHz) ie: divides the clock by some number.
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        Currently set to a prescaler of 8 because that is what the orb and servos use (they are on this timer as well)
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        See page137 in Atemga128 Docs for all the available prescalers */
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  TCCR3B |= _BV(CS31);
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  /*         Sets the two regsiters that we compare against. So the timer counts up to this number and
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        then resets back to 0 and calls the compare match interrupt.
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        8x10^6 / 8 = 1/16 Second. All values are based off of this number. Do not change it unless you
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        are l337*/
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  OCR3A = 0xF424;        
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  /*         Enable Output Compare A Interrupt. When OCR3A is met by the timer TCNT3 this interrupt will be
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        triggerd. (See page140 in Atmega128 Docs for more information */
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  ETIMSK |= _BV(OCIE3A);
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  /*        Store the pointer to the function to be used in the interrupt */
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  _rtc_f = rtc_func;
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  /*        Store how many 1/16ths of a second you want to let by before triggering an interrupt */
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  _rtc_scale = prescale_opt;
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}
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/**
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 * Returns the time elapsed in seconds since the last call to
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 * rtc_init or rtc_reset.
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 *
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 * @return the number of seconds since the last call to rtc_init or rtc_reset
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 *
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 * @see rtc_init, rtc_reset
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 **/
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int rtc_get(void) {
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  return _rtc_val;
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}
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/**
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 * Resets the real time clock counter to 0.
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 *
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 * @see rtc_init, rtc_get
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 **/
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void rtc_reset(void) {
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  _rtc_val = 0;
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}
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/** @} **/ //end defgroup
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/*        Called every pulse. Function in _rtc_f is called every _rtc_scale and also the counter is updated.
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        Bascially, since the pulse is hard set at 1/16s  you want to count how many 16ths of a second have passed
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        and when it reaches the amount of time you want, execute the code. */
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SIGNAL(TIMER3_COMPA_vect) {
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  if (_rtc_pulse ==  _rtc_scale) {
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    //Increment the real time clock counter
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    _rtc_val++;
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    //Calls the function tied to the real time clock if defined
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    if(_rtc_f != 0)
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      _rtc_f();
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    //Resets the pulse until the next scale is matched
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    _rtc_pulse = 0;
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  }        
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  //Updates the amount of pulses seen since the last scale match
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  _rtc_pulse++;
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}