skarg
140 lines
4.6 KiB
C
140 lines
4.6 KiB
C
/**************************************************************************
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*
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* Copyright (C) 2009 Steve Karg <skarg@users.sourceforge.net>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* 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 OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*********************************************************************/
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#include <stdbool.h>
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#include <stdint.h>
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#include "hardware.h"
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#include "timer.h"
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/* Timer2 Prescaling: 1, 8, 32, 64, 128, 256, or 1024 */
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#define TIMER2_PRESCALER 128
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/* Count: Timer counts up to 0xFF and then signals overflow */
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#define TIMER2_TICKS (F_CPU/TIMER2_PRESCALER/1000)
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#if (TIMER2_TICKS > 0xFF)
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#error Timer2 Prescaler value is too small
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#endif
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#define TIMER2_COUNT (0xFF-TIMER2_TICKS)
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/* counter for the the timer which wraps every 49.7 days */
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static volatile uint32_t Millisecond_Counter;
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/*************************************************************************
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* Description: Timer Interrupt Service Routine - Timer Overflowed!
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* Returns: none
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* Notes: Global interupts must be enabled
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*************************************************************************/
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ISR(TIMER2_OVF_vect)
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{
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/* Set the counter for the next interrupt */
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TCNT2 = TIMER2_COUNT;
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Millisecond_Counter++;
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}
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/*************************************************************************
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* Description: sets the current time count with a value
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* Returns: none
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* Notes: none
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*************************************************************************/
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uint32_t timer_milliseconds_set(
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uint32_t value)
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{
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uint8_t sreg = 0; /* holds interrupts pending */
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uint32_t old_value = 0; /* return value */
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sreg = SREG;
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__disable_interrupt();
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old_value = Millisecond_Counter;
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Millisecond_Counter = value;
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SREG = sreg;
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return old_value;
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}
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/*************************************************************************
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* Description: returns the current millisecond count
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* Returns: none
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* Notes: none
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*************************************************************************/
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uint32_t timer_milliseconds(
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void)
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{
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uint32_t timer_value = 0; /* return value */
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uint8_t sreg = 0; /* holds interrupts pending */
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sreg = SREG;
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__disable_interrupt();
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timer_value = Millisecond_Counter;
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SREG = sreg;
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return timer_value;
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}
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/*************************************************************************
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* Description: Initialization for Timer
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* Returns: none
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* Notes: none
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*************************************************************************/
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void timer_init(
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void)
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{
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/* Normal Operation */
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TCCR2A = 0;
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/* Timer2: prescale selections:
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CSn2 CSn1 CSn0 Description
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---- ---- ---- -----------
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0 0 0 No Clock Source
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0 0 1 No prescaling
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0 1 0 CLKt2s/8
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0 1 1 CLKt2s/32
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1 0 0 CLKt2s/64
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1 0 1 CLKt2s/128
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1 1 0 CLKt2s/256
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1 1 1 CLKt2s/1024
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*/
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#if (TIMER2_PRESCALER==1)
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TCCR2B = _BV(CS20);
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#elif (TIMER2_PRESCALER==8)
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TCCR2B = _BV(CS21);
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#elif (TIMER2_PRESCALER==32)
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TCCR2B = _BV(CS21) | _BV(CS20);
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#elif (TIMER2_PRESCALER==64)
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TCCR2B = _BV(CS22);
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#elif (TIMER2_PRESCALER==128)
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TCCR2B = _BV(CS22) | _BV(CS20);
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#elif (TIMER2_PRESCALER==256)
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TCCR2B = _BV(CS22) | _BV(CS21);
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#elif (TIMER2_PRESCALER==1024)
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TCCR2B = _BV(CS22) | _BV(CS21) | _BV(CS20);
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#else
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#error Timer2 Prescale: Invalid Value
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#endif
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/* Clear any TOV Flag set when the timer overflowed */
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BIT_CLEAR(TIFR2, TOV2);
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/* Initial value */
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TCNT2 = TIMER2_COUNT;
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/* Enable the overflow interrupt */
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BIT_SET(TIMSK2, TOIE2);
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/* Clear the Power Reduction Timer/Counter0 */
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BIT_CLEAR(PRR, PRTIM2);
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}
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