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         case 6: // buttons: 1.1V, ADC3, single-ended
  47                 PORTA |= _BV(PA3); // +5V to the voltage splitter
  48                 ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
  49                 sum_shift = 0;
  50                 break;
  51         }
  52
  53         adc_sum = 0;
  54         adc_vals = 1 << sum_shift;
  55 }
  56
  57 static void start_next_adc()
  58 {
  59         if (current_adc > 0)
  60                 current_adc--;
  61         else
  62                 // TODO: kick the watchdog here.
  63                 current_adc = NUM_ADCS-1;
  64
  65         // set up mux, start one-shot conversion
  66         setup_mux(current_adc);
  67         ADCSRA |= _BV(ADSC);
  68 }
  69
  70 /*
  71  * Single synchronous ADC conversion.
  72  * Has to be called with IRQs disabled (or with the ADC IRQ disabled).
  73  */
  74 static uint16_t read_adc_sync()
  75 {
  76         uint16_t rv;
  77
  78         ADCSRA |= _BV(ADSC); // start the conversion
  79
  80         // wait for the conversion to finish
  81         while((ADCSRA & _BV(ADIF)) == 0)
  82                 ;
  83
  84         rv = ADCW;
  85         ADCSRA |= _BV(ADIF); // clear the IRQ flag
  86
  87         return rv;
  88 }
  89
  90 void init_adc()
  91 {
  92         unsigned char i;
  93         current_adc = NUM_ADCS;
  94
  95         ADCSRA = _BV(ADEN)                      // enable
  96                 | _BV(ADPS1) | _BV(ADPS0)       // CLK/8 = 125 kHz
  97                 // | _BV(ADPS2)                 // CLK/16 = 62.5 kHz
  98                 ;
  99         // ADCSRB |= _BV(GSEL); // gain 8 or 32
 100
 101         // Disable digital input on all bits used by ADC
 102         DIDR0 = _BV(ADC0D) | _BV(ADC1D) | _BV(ADC2D) | _BV(ADC3D)
 103                 | _BV(ADC4D) | _BV(ADC5D) | _BV(ADC6D);
 104
 105         // 1.1V, ADC1,1, gain 20
 106         ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
 107
 108         /* Do first conversion and drop the result */
 109         read_adc_sync();
 110
 111         adc1_gain20_offset = 0;
 112
 113         for (i = 0; i < (1 << ADC1_GAIN20_OFFSET_SHIFT); i++) {
 114                 adc1_gain20_offset += read_adc_sync()
 115                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 116         }
 117
 118         ADCSRA |= _BV(ADIE); // enable IRQ
 119
 120         start_next_adc();
 121 }
 122
 123 void susp_adc()
 124 {
 125         ADCSRA = 0;
 126         DIDR0 = 0;
 127 }
 128
 129 ISR(ADC_vect) { // IRQ handler
 130         uint16_t adcval = ADCW;
 131
 132         if (adc_vals)
 133                 // start the next conversion immediately
 134                 ADCSRA |= _BV(ADSC);
 135
 136         if (adc_vals < (1 << sum_shift))
 137                  // drop the first conversion, use all others
 138                  adc_sum += adcval;
 139
 140         if (adc_vals) {
 141                 adc_vals--;
 142                 return;
 143         }
 144
 145         // Now handle the (1 << sum_shift) measurements
 146
 147         adcval = adc_sum >> sum_shift;
 148
 149         if (current_adc == ADC1_GAIN20) {
 150                 // running average
 151                 adc1_gain20_offset += adcval
 152                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 153         } else if (current_adc == 0 || current_adc == 1) {
 154                 uint16_t offset = adc1_gain20_offset
 155                         >> (ADC1_GAIN20_OFFSET_SHIFT - sum_shift);
 156                 if (adc_sum > offset)
 157                         adc_sum -= offset;
 158                 else
 159                         adc_sum = 0;
 160         }
 161
 162         if (current_adc < N_PWMLEDS)
 163                 pwmled_adc(current_adc, adc_sum);
 164         if (current_adc == AMBIENT_ADC)
 165                 ambient_adc(adc_sum);
 166         if (current_adc == BATTERY_ADC)
 167                 battery_adc(adcval);
 168         if (current_adc == BUTTON_ADC)
 169                 button_adc(adcval);
 170
 171         start_next_adc();
 172 }
 173