firmware/adc.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3
   4 #include "lights.h"
   5
   6 #define AMBIENT_ADC N_PWMLEDS
   7 #define BATTERY_ADC (N_PWMLEDS + 1)
   8 #define ADC1_GAIN20 (N_PWMLEDS + 2)
   9 #define BUTTON_ADC  (N_PWMLEDS + 2)
  10
  11 #define NUM_ADCS 7
  12 volatile static unsigned char current_adc;
  13 static uint16_t adc_sum;
  14 static unsigned char sum_shift;
  15 static unsigned char adc_vals;
  16 #define ADC1_GAIN20_OFFSET_SHIFT        6
  17 static uint16_t adc1_gain20_offset;
  18
  19 static void inline setup_mux(unsigned char n)
  20 {
  21         /* ADC numbering: PWM LEDs first, then ambient light sensor, battery sensor */
  22         switch (n) {
  23         case 0: // pwmled 1: 1.1V, ADC0,1 (PA0,1), gain 20
  24                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX1) | _BV(MUX0);
  25                 sum_shift = PWMLED_ADC_SHIFT;
  26                 break;
  27         case 1: // pwmled 2: 1.1V, ADC2,1 (PA2,1), gain 20
  28                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  29                 sum_shift = PWMLED_ADC_SHIFT;
  30                 break;
  31         case 2: // pwmled 3: 1.1V, ADC4 (PA5), single-ended
  32                 ADMUX = _BV(REFS1) | _BV(MUX2);
  33                 sum_shift = PWMLED_ADC_SHIFT;
  34                 break;
  35         case 3: // ambient light: 1.1V, ADC5 (PA6), single-ended
  36                 ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX0);
  37                 sum_shift = 3; // 3 measurements
  38                 break;
  39         case 4: // batt voltage: 1.1V, ADC6 (PA7), single-ended
  40                 ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX1);
  41                 sum_shift = 0; // 1 measurement
  42                 break;
  43         case 5: // gain stage offset: 1.1V, ADC1,1, gain 20
  44                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
  45                 sum_shift = 0; // 1 measurement
  46                 break;
  47         case 6: // buttons: 1.1V, ADC3, single-ended
  48                 PORTA |= _BV(PA3); // +5V to the voltage splitter
  49                 ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
  50                 sum_shift = 0;
  51                 break;
  52         }
  53
  54         adc_sum = 0;
  55         adc_vals = 1 << sum_shift;
  56 }
  57
  58 static void start_next_adc()
  59 {
  60         if (current_adc > 0)
  61                 current_adc--;
  62         else
  63                 // TODO: kick the watchdog here.
  64                 current_adc = NUM_ADCS-1;
  65
  66         // set up mux, start one-shot conversion
  67         setup_mux(current_adc);
  68         ADCSRA |= _BV(ADSC);
  69 }
  70
  71 /*
  72  * Single synchronous ADC conversion.
  73  * Has to be called with IRQs disabled (or with the ADC IRQ disabled).
  74  */
  75 static uint16_t read_adc_sync()
  76 {
  77         uint16_t rv;
  78
  79         ADCSRA |= _BV(ADSC); // start the conversion
  80
  81         // wait for the conversion to finish
  82         while((ADCSRA & _BV(ADIF)) == 0)
  83                 ;
  84
  85         rv = ADCW;
  86         ADCSRA |= _BV(ADIF); // clear the IRQ flag
  87
  88         return rv;
  89 }
  90
  91 void init_adc()
  92 {
  93         unsigned char i;
  94         current_adc = NUM_ADCS;
  95
  96         ADCSRA = _BV(ADEN)                      // enable
  97                 | _BV(ADPS1) | _BV(ADPS0)       // CLK/8 = 125 kHz
  98                 // | _BV(ADPS2)                 // CLK/16 = 62.5 kHz
  99                 ;
 100         // ADCSRB |= _BV(GSEL); // gain 8 or 32
 101
 102         // Disable digital input on all bits used by ADC
 103         DIDR0 = _BV(ADC0D) | _BV(ADC1D) | _BV(ADC2D) | _BV(ADC3D)
 104                 | _BV(ADC4D) | _BV(ADC5D) | _BV(ADC6D);
 105
 106         // 1.1V, ADC1,1, gain 20
 107         ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
 108
 109         /* Do first conversion and drop the result */
 110         read_adc_sync();
 111
 112         adc1_gain20_offset = 0;
 113
 114         for (i = 0; i < (1 << ADC1_GAIN20_OFFSET_SHIFT); i++) {
 115                 adc1_gain20_offset += read_adc_sync()
 116                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 117         }
 118
 119         ADCSRA |= _BV(ADIE); // enable IRQ
 120
 121         start_next_adc();
 122 }
 123
 124 void susp_adc()
 125 {
 126         ADCSRA = 0;
 127         DIDR0 = 0;
 128 }
 129
 130 ISR(ADC_vect) { // IRQ handler
 131         uint16_t adcval = ADCW;
 132
 133         if (adc_vals)
 134                 // start the next conversion immediately
 135                 ADCSRA |= _BV(ADSC);
 136
 137         if (adc_vals < (1 << sum_shift))
 138                  // drop the first conversion, use all others
 139                  adc_sum += adcval;
 140
 141         if (adc_vals) {
 142                 adc_vals--;
 143                 return;
 144         }
 145
 146         // Now handle the (1 << sum_shift) measurements
 147
 148         adcval = adc_sum >> sum_shift;
 149
 150         if (current_adc == ADC1_GAIN20) {
 151                 // running average
 152                 adc1_gain20_offset += adcval
 153                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 154         } else if (current_adc == 0 || current_adc == 1) {
 155                 uint16_t offset = adc1_gain20_offset
 156                         >> (ADC1_GAIN20_OFFSET_SHIFT - sum_shift);
 157                 if (adc_sum > offset)
 158                         adc_sum -= offset;
 159                 else
 160                         adc_sum = 0;
 161         }
 162
 163         if (current_adc < N_PWMLEDS)
 164                 pwmled_adc(current_adc, adc_sum);
 165         if (current_adc == AMBIENT_ADC)
 166                 ambient_adc(adc_sum);
 167         if (current_adc == BATTERY_ADC)
 168                 battery_adc(adcval);
 169         if (current_adc == BUTTON_ADC)
 170                 button_adc(adcval);
 171
 172         start_next_adc();
 173 }
 174