projects/step-up/pwm.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <avr/power.h>
   4 #include <util/delay.h>
   5 #include <util/atomic.h>
   6
   7 #include "lights.h"
   8
   9 /*
  10  * Single PWM channel on OC1B (pin PB4 of Tiny45).
  11  * Counts from 0 to 0xFF, without OCR1C compare.
  12  */
  13
  14 volatile unsigned char pwm_enabled;
  15
  16 static void inline enable_pll()
  17 {
  18         /* Async clock */
  19         PLLCSR = _BV(PLLE) | _BV(LSM);
  20
  21         /* Synchronize to the phase lock */
  22         _delay_us(100);
  23         while ((PLLCSR & _BV(PLOCK)) == 0)
  24                 ;
  25         PLLCSR |= _BV(PCKE);
  26 }
  27
  28 void init_pwm()
  29 {
  30         pwm_enabled = 0;
  31         power_timer1_enable();
  32
  33         TCCR1 = _BV(CTC1) | _BV(CS11);  // pll_clk/2
  34         GTCCR = _BV(COM1B1) | _BV(PWM1B);
  35
  36         OCR1C = PWM_MAX;
  37         OCR1B = 0;              // initial stride is 0
  38
  39         DDRB &= ~(_BV( PB4 ));
  40         PORTB &= ~_BV(PB4); // set to zero
  41 }
  42
  43 void susp_pwm()
  44 {
  45         DDRB &= ~(_BV( PB4 ));
  46         PORTB &= ~(_BV( PB4 ));
  47         TCCR1 = 0;
  48         TIMSK = 0;
  49         TIFR = 0;
  50
  51         PLLCSR &= ~(_BV(PLLE) | _BV(PCKE));
  52 }
  53
  54 void pwm_off()
  55 {
  56         OCR1B = 0;
  57         DDRB &= ~_BV(PB4);
  58
  59         PLLCSR &= ~(_BV(PLLE) | _BV(PCKE));
  60         power_timer1_disable();
  61         pwm_enabled = 0;
  62 }
  63
  64 void pwm_set(uint8_t stride)
  65 {
  66         OCR1B = stride;
  67
  68         if (!pwm_enabled) {
  69                 power_timer1_enable();
  70                 enable_pll();
  71                 DDRB |= _BV(PB4);
  72                 pwm_enabled = 1;
  73         }
  74 }