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johnhooks/clock_and_pwm.c

Last active June 30, 2018 14:51
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Revisions

  1. johnhooks revised this gist Jun 30, 2018. 1 changed file with 1 addition and 1 deletion.
    2 changes: 1 addition & 1 deletion clock_and_pwm.c
    View file
    Original file line number Diff line number Diff line change
    @@ -12,7 +12,7 @@ static volatile uint16_t microseconds = 0; /* Should never be more than 1000 */

    ISR(TIMER0_OVF_vect) {
    /* Each overflow will be approximately 2 milliseconds and 6 microseconds */
    if (_microseconds >= 996) {
    if (microseconds >= 996) {
    microseconds = 2;
    milliseconds += 3;
    } else {
  2. johnhooks revised this gist Jun 30, 2018. 1 changed file with 4 additions and 4 deletions.
    8 changes: 4 additions & 4 deletions clock_and_pwm.c
    View file
    Original file line number Diff line number Diff line change
    @@ -13,11 +13,11 @@ static volatile uint16_t microseconds = 0; /* Should never be more than 1000 */
    ISR(TIMER0_OVF_vect) {
    /* Each overflow will be approximately 2 milliseconds and 6 microseconds */
    if (_microseconds >= 996) {
    _microseconds = 2;
    _milliseconds += 3;
    microseconds = 2;
    milliseconds += 3;
    } else {
    _microseconds += 6;
    _milliseconds += 2;
    microseconds += 6;
    milliseconds += 2;
    }
    }

  3. johnhooks created this gist Jun 30, 2018.
    55 changes: 55 additions & 0 deletions clock_and_pwm.c
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,55 @@
    /**
    * I want to use a counter/timer for PWM and as a rudimentary
    * millisecond clock. If I initiate the counter in Fast PWM mode,
    * using a clock speed of 1MHz and a prescale of 8, a millisecond will
    * elapse every 125 clock ticks.
    */

    typedef uint32_t millis_t;

    static volatile millis_t milliseconds = 0; /* 49.71 Days of milliseconds */
    static volatile uint16_t microseconds = 0; /* Should never be more than 1000 */

    ISR(TIMER0_OVF_vect) {
    /* Each overflow will be approximately 2 milliseconds and 6 microseconds */
    if (_microseconds >= 996) {
    _microseconds = 2;
    _milliseconds += 3;
    } else {
    _microseconds += 6;
    _milliseconds += 2;
    }
    }

    millis_t millis()
    {
    millis_t ms;
    ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
    {
    ms = milliseconds;
    }
    return ms;
    }

    void init(void)
    {
    /* Timer 0A */
    TCCR0A |= (1 << WGM00); /* Fast PWM mode, 8-bit */
    TCCR0A |= (1 << WGM01); /* Fast PWM mode, pt.2 */
    TCCR0B |= (1 << CS01); /* PWM Freq = F_CPU/8/256 */
    TCCR0A |= (1 << COM0A1); /* PWM output on OCR0A */
    sei();
    }

    void main(void)
    {
    init();

    while (1) {
    /* set OCROA to what ever PWM value I want, while also able to read millis() */
    }

    return(0);
    }