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// Yep, this is actually -*- c++ -*-
#ifndef _TIMER1_H_
#define _TIMER1_H_
//these routines provide an easy interface for controlling timer1 interrupts
inline void enableTimer1Interrupt()
{
TIMSK1 |= (1<<OCIE1A);
}
inline void disableTimer1Interrupt()
{
TIMSK1 &= ~(1<<OCIE1A);
TIMSK1 &= ~(1<<ICIE1);
}
inline void setTimer1Resolution(byte r)
{
//from table 15-5 in that atmega168 datasheet:
// we're setting CS12 - CS10 which correspond to the binary numbers 0-5
// 0 = no timer
// 1 = no prescaler
// 2 = clock/8
// 3 = clock/64
// 4 = clock/256
// 5 = clock/1024
if (r > 5)
r = 5;
TCCR1B &= B11111000;
TCCR1B |= r;
}
inline void setTimer1Ceiling(unsigned int c)
{
OCR1A = c;
}
unsigned int getTimer1Ceiling(unsigned long ticks)
{
// our slowest speed at our highest resolution ( (2^16-1) * 0.0625 usecs = 4095 usecs)
if (ticks <= 65535L)
return (ticks & 0xffff);
// our slowest speed at our next highest resolution ( (2^16-1) * 0.5 usecs = 32767 usecs)
else if (ticks <= 524280L)
return ((ticks / 8) & 0xffff);
// our slowest speed at our medium resolution ( (2^16-1) * 4 usecs = 262140 usecs)
else if (ticks <= 4194240L)
return ((ticks / 64) & 0xffff);
// our slowest speed at our medium-low resolution ( (2^16-1) * 16 usecs = 1048560 usecs)
else if (ticks <= 16776960L)
return (ticks / 256);
// our slowest speed at our lowest resolution ((2^16-1) * 64 usecs = 4194240 usecs)
else if (ticks <= 67107840L)
return (ticks / 1024);
//its really slow... hopefully we can just get by with super slow.
else
return 65535;
}
byte getTimer1Resolution(unsigned long ticks)
{
// these also represent frequency: 1000000 / ticks / 2 = frequency in hz.
// our slowest speed at our highest resolution ( (2^16-1) * 0.0625 usecs = 4095 usecs (4 millisecond max))
// range: 8Mhz max - 122hz min
if (ticks <= 65535L)
return 1;
// our slowest speed at our next highest resolution ( (2^16-1) * 0.5 usecs = 32767 usecs (32 millisecond max))
// range:1Mhz max - 15.26hz min
else if (ticks <= 524280L)
return 2;
// our slowest speed at our medium resolution ( (2^16-1) * 4 usecs = 262140 usecs (0.26 seconds max))
// range: 125Khz max - 1.9hz min
else if (ticks <= 4194240L)
return 3;
// our slowest speed at our medium-low resolution ( (2^16-1) * 16 usecs = 1048560 usecs (1.04 seconds max))
// range: 31.25Khz max - 0.475hz min
else if (ticks <= 16776960L)
return 4;
// our slowest speed at our lowest resolution ((2^16-1) * 64 usecs = 4194240 usecs (4.19 seconds max))
// range: 7.812Khz max - 0.119hz min
else if (ticks <= 67107840L)
return 5;
//its really slow... hopefully we can just get by with super slow.
else
return 5;
}
inline void setTimer1Ticks(unsigned long ticks)
{
// ticks is the delay between interrupts in 62.5 nanosecond ticks.
//
// we break it into 5 different resolutions based on the delay.
// then we set the resolution based on the size of the delay.
// we also then calculate the timer ceiling required. (ie what the counter counts to)
// the result is the timer counts up to the appropriate time and then fires an interrupt.
setTimer1Ceiling(getTimer1Ceiling(ticks));
setTimer1Resolution(getTimer1Resolution(ticks));
}
inline void setTimer1Micros(unsigned long micros)
{
//16 ticks in a microsecond.
unsigned long ticks = micros * 16;
setTimer1Ticks(ticks);
}
void setupTimer1Interrupt()
{
//clear the registers
TCCR1A = 0;
TCCR1B = 0;
TCCR1C = 0;
TIMSK1 = 0;
//waveform generation = 0100 = CTC
TCCR1B &= ~(1<<WGM13);
TCCR1B |= (1<<WGM12);
TCCR1A &= ~(1<<WGM11);
TCCR1A &= ~(1<<WGM10);
//output mode = 00 (disconnected)
TCCR1A &= ~(1<<COM1A1);
TCCR1A &= ~(1<<COM1A0);
TCCR1A &= ~(1<<COM1B1);
TCCR1A &= ~(1<<COM1B0);
//start off with a slow frequency.
setTimer1Resolution(5);
setTimer1Ceiling(65535);
disableTimer1Interrupt();
}
#endif
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