projects/step-up/pwm.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <util/delay.h>
   4 #include <util/atomic.h>
   5
   6 #include "lights.h"
   7
   8 #define PWM_STEP_SHIFT 2 /* sub-LSB precision */
   9 #define PWM_TOP (((PWM_MAX) + (4 << (PWM_STEP_SHIFT))) >> (PWM_STEP_SHIFT))
  10 #if PWM_TOP > 0x0FF
  11 #error PWM_TOP too high
  12 #endif
  13
  14 static uint16_t pwm[N_PWMLEDS];
  15 static volatile unsigned char step;
  16
  17 static void enable_pll()
  18 {
  19         /* Async clock */
  20         PLLCSR = _BV(PLLE);
  21
  22         /* Synchronize to the phase lock */
  23         _delay_us(100);
  24         while ((PLLCSR & _BV(PLOCK)) == 0)
  25                 ;
  26         PLLCSR |= _BV(PCKE);
  27 }
  28
  29 void init_pwm()
  30 {
  31         int i;
  32
  33         step = 0;
  34
  35         for (i = 0; i < N_PWMLEDS; i++)
  36                 pwm[i] = 0;
  37
  38         enable_pll();
  39
  40         TCCR1 = _BV(CTC1) | _BV(CS10);  // no clock prescaling
  41         GTCCR = _BV(COM1A1) | _BV(COM1B1) | _BV(PWM1A) | _BV(PWM1B);
  42
  43         OCR1C = PWM_TOP;
  44         OCR1A = OCR1B = 0;              // initial stride is 0
  45
  46         DDRB  &= ~(_BV( PB1 ) | _BV( PB4 )); // tristate it
  47         PORTB &= ~(_BV( PB1 ) | _BV( PB4 )); // set to zero
  48 }
  49
  50 #if 0
  51 void susp_pwm()
  52 {
  53         unsigned char i;
  54
  55         for (i = 0; i < N_PWMLEDS; i++)
  56                 pwm[i] = 0;
  57
  58         DDRB &= ~(_BV( PB1 ) | _BV( PB3 ) | _BV( PB5 ));
  59         TCCR1D = TCCR1C = TCCR1B = TCCR1A = 0;
  60         TIMSK = 0;
  61         TIFR = 0;
  62
  63         PLLCSR &= ~(_BV(PLLE) | _BV(PCKE));
  64 }
  65 #endif
  66
  67 void pwm_off(unsigned char n)
  68 {
  69         ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
  70                 pwm[n] = 0;
  71
  72                 switch (n) {
  73                 case 0: DDRB &= ~_BV(PB1); break;
  74                 case 1: DDRB &= ~_BV(PB4); break;
  75                 }
  76         }
  77 }
  78
  79 static void pwm_update_hw(unsigned char n)
  80 {
  81         uint16_t stride = (pwm[n] + step) >> PWM_STEP_SHIFT;
  82
  83         switch (n) {
  84         case 0:
  85                 OCR1A = stride;
  86                 break;
  87         case 1:
  88                 OCR1B = stride;
  89                 break;
  90         }
  91 }
  92
  93 void pwm_set(unsigned char n, uint16_t stride)
  94 {
  95         if (stride > PWM_MAX)
  96                 stride = PWM_MAX;
  97
  98         ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
  99                 pwm[n] = stride;
 100
 101                 pwm_update_hw(n);
 102
 103                 switch(n) {
 104                 case 0: DDRB |= _BV(PB1); break;
 105                 case 1: DDRB |= _BV(PB4); break;
 106                 }
 107         }
 108 }
 109
 110 void pwm_timer()
 111 {
 112         unsigned char i;
 113
 114         if (++step >= (1 << PWM_STEP_SHIFT))
 115                 step = 0;
 116
 117         for (i = 0; i < N_PWMLEDS; i++)
 118                 if (pwm[i])
 119                         pwm_update_hw(i);
 120 }
 121