1

#include <avr/io.h>

     2

#include "stdlib.h"

     3

     4

#include <avr/interrupt.h>

     5

     6

#define TIMER_FLAGS     GPIOR0

     7

#define TIMER1_BUSY     1

     8

     9

/*

    10

 * Setup timers.

    11

 */

    12

void timer_init (void)

    13

{

    14

    TCCR1A = (

    15

            // OC1A output pin disconnected

    16

            0b00 << COM1A0

    17

            // OC1B output pin disconnected

    18

        |   0b00 << COM1B0

    19

            // no PWM

    20

        |   0b00 << WGM10

    21

    );

    22

    TCCR1B = (

    23

            // CTC mode

    24

            0b01 << WGM12 

    25

    );

    26

    TCCR1C = 0;

    27

}

    28

    29

void timer1_start (short cycles)

    30

{

    31

    // count up from zero...

    32

    TCNT1 = 0;

    33

    34

    // ...to the given number of timer cycles

    35

    OCR1A = cycles;

    36

    37

    // start!

    38

    sbi(&TIMER_FLAGS, TIMER1_BUSY);

    39

    TIMSK1 = (

    40

            // OCA interrupt

    41

            0b1 << OCIE1A       // enable

    42

    );

    43

    TCCR1B = (

    44

            // WGM

    45

            0b01  << WGM12      // CTC

    46

    47

            // clocksource

    48

        |   0b101 << CS10       // 1024'th

    49

    );

    50

}

    51

    52

static void timer1_stop ()

    53

{

    54

    // WGM: normal

    55

    // clocksource: stop

    56

    TCCR1B = 0;

    57

    58

    cbi(&TIMER_FLAGS, TIMER1_BUSY);

    59

}

    60

    61

ISR(TIMER1_COMPA_vect)

    62

{

    63

    timer1_stop();

    64

    65

    // XXX: cpu will automatically wake up from sleep()

    66

}

    67

    68

/*

    69

 * Sleep on timer1 interrupt.

    70

 */

    71

void timer_sleep (int cycles)

    72

{

    73

    // set timer

    74

    timer1_start(cycles);

    75

    76

    // sleep

    77

    // TODO: PRR

    78

    SMCR = (

    79

            // idle sleep

    80

            (0b00 << SM0)

    81

    82

            // enable sleep

    83

        |   (0b1 << SE)

    84

    );

    85

    86

    // sleep

    87

    while (tbi(&TIMER_FLAGS, TIMER1_BUSY)) {

    88

        __asm__ ( "sleep" :: );

    89

    }

    90

    91

    // cleanup

    92

    SMCR = 0;

    93

}

    94

    95

int main (void)

    96

{

    97

    timer_init();

    98

    99

    // LED

   100

    sbi(&DDRB, DDB5);

   101

   102

    sei();

   103

   104

    // blink

   105

    short timeout = 1000;

   106

    short delta = 10;

   107

   108

    while (true) {

   109

        // bitflip

   110

        xbi(&PORTB, PORTB5);

   111

   112

        timer_sleep(timeout);

   113

   114

        timeout += delta;

   115

    }

   116

}