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Counter.cpp
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Counter.cpp
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/*
Simple library for Arduino implementing a hardware counter
for a Geigier counter for example
Copyright (c) 2011, Robin Scheibler aka FakuFaku
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of the <organization> nor the
names of its contributors may be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "Counter.h"
#include <limits.h>
// need to have the global variable to count
// overflows
unsigned int g_ovf_n;
// Constructor
HardwareCounter::HardwareCounter(int timer_pin, long delay)
{
// register delay
_delay = delay;
// register timer pin
_pin = timer_pin;
}
// call this to start the counter
void HardwareCounter::start()
{
// set pin as digital input
pinMode(_pin, INPUT);
// hardware counter setup ( refer atmega168.pdf chapter 16-bit counter1)
TIMSKn = 0; // disable overflow interrupt
TCCRnA = 0; // reset timer/countern control register A
TCCRnB = 0; // reset timer/countern control register A
// Reset the counter to zero
TCNTn = 0; // counter register value = 0
g_ovf_n = 0; // reset number of overflows
_count = 0; // set count to zero (optional)
// set overflow interrupt
TIFR1 |= 1; // clear overflow interrupt flag
TIMSKn |= _BV(TOIEn); // enable overflow interrupt
// set start time
_start_time = millis();
// start counting now
TCCRnB = _BV(CS10) | _BV(CS11) | _BV(CS12); // Counter Clock source = pin Tn , start counting now
}
// call this to read the current count and save it
unsigned long HardwareCounter::count()
{
TCCRnB = TCCRnB & ~7; // Gate Off / Counter Tn stopped
_count = TCNTn; // Set the count in object variable
TCCRnB = TCCRnB | 7; // restart counting
return 0xfffful*g_ovf_n + _count;
}
// This indicates when the count over the determined period is over
int HardwareCounter::available()
{
// get current time
unsigned long now = millis();
// do basic check for millis overflow
if (now >= _start_time)
return (now - _start_time >= _delay);
else
return (ULONG_MAX + now - _start_time >= _delay);
}
// This takes care of the counter overflow problem
ISR(TIMERn_OVF_vect)
{
// increment number of overflows
g_ovf_n++;
}