common/sleep_led.c

   1 #include <stdint.h>
   2 #include <avr/io.h>
   3 #include <avr/interrupt.h>
   4 #include <avr/pgmspace.h>
   5 #include "led.h"
   6 #include "sleep_led.h"
   7
   8 /* Software PWM
   9  *  ______           ______           __
  10  * |  ON  |___OFF___|  ON  |___OFF___|   ....
  11  * |<-------------->|<-------------->|<- ....
  12  *     PWM period       PWM period
  13  *
  14  * 256              interrupts/period[resolution]
  15  * 64               periods/second[frequency]
  16  * 256*64           interrupts/second
  17  * F_CPU/(256*64)   clocks/interrupt
  18  */
  19 #define SLEEP_LED_TIMER_TOP F_CPU/(256*64)
  20
  21 void sleep_led_init(void)
  22 {
  23     /* Timer1 setup */
  24     /* CTC mode */
  25     TCCR1B |= _BV(WGM12);
  26     /* Clock selelct: clk/1 */
  27     TCCR1B |= _BV(CS10);
  28     /* Set TOP value */
  29     uint8_t sreg = SREG;
  30     cli();
  31     OCR1AH = (SLEEP_LED_TIMER_TOP>>8)&0xff;
  32     OCR1AL = SLEEP_LED_TIMER_TOP&0xff;
  33     SREG = sreg;
  34 }
  35
  36 void sleep_led_enable(void)
  37 {
  38     /* Enable Compare Match Interrupt */
  39     TIMSK1 |= _BV(OCIE1A);
  40 }
  41
  42 void sleep_led_disable(void)
  43 {
  44     /* Disable Compare Match Interrupt */
  45     TIMSK1 &= ~_BV(OCIE1A);
  46 }
  47
  48
  49 /* Breathing Sleep LED brighness(PWM On period) table
  50  * (32[steps] * 8[duration]) / 64[PWM periods/s] = 4 second breath cycle
  51  */
  52 static const uint8_t breathing_table[32] PROGMEM = {
  53     0, 0, 0, 2, 9, 21, 37, 56, 78, 127, 151, 175, 197, 216, 232, 244,
  54     254, 244, 216, 197, 175, 151, 127, 78, 56, 37, 21, 9, 2, 0, 0, 0
  55 };
  56
  57 ISR(TIMER1_COMPA_vect)
  58 {
  59     /* Software PWM
  60      * timer:1111 1111 1111 1111
  61      *       \----/\-/ \-------/+---  count(0-255)
  62      *         |    +---------------  duration of step(8)
  63      *         +--------------------  index of step table(0-31)
  64      */
  65     static union {
  66         uint16_t row;
  67         struct {
  68             uint8_t count:8;
  69             uint8_t duration:3;
  70             uint8_t index:5;
  71         } pwm;
  72     } timer = { .row = 0 };
  73
  74     timer.row++;
  75
  76     // LED on
  77     if (timer.pwm.count == 0) {
  78         led_set(1<<USB_LED_CAPS_LOCK);
  79     }
  80     // LED off
  81     if (timer.pwm.count == pgm_read_byte(&breathing_table[timer.pwm.index])) {
  82         led_set(0);
  83     }
  84 }