firmware/adc.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <util/atomic.h>
   4
   5 #include "lights.h"
   6
   7 #define AMBIENT_ADC N_PWMLEDS
   8 #define BATTERY_ADC (N_PWMLEDS + 1)
   9 #define ADC1_GAIN20 (N_PWMLEDS + 2)
  10
  11 #define NUM_ADCS 6
  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 static unsigned char handler_running;
  19
  20 static void inline setup_mux(unsigned char n)
  21 {
  22         /* ADC numbering: PWM LEDs first, then ambient light sensor, battery sensor */
  23         switch (n) {
  24         case 0: // pwmled 1: 1.1V, ADC0,1 (PA0,1), gain 20
  25                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX1) | _BV(MUX0);
  26                 sum_shift = PWMLED_ADC_SHIFT;
  27                 break;
  28         case 1: // pwmled 2: 1.1V, ADC2,1 (PA2,1), gain 20
  29                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  30                 sum_shift = PWMLED_ADC_SHIFT;
  31                 break;
  32         case 2: // pwmled 3: 1.1V, ADC4 (PA5), single-ended
  33                 ADMUX = _BV(REFS1) | _BV(MUX2);
  34                 sum_shift = PWMLED_ADC_SHIFT;
  35                 break;
  36         case 3: // ambient light: 1.1V, ADC5 (PA6), single-ended
  37                 ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX0);
  38                 sum_shift = 3; // 3 measurements
  39                 break;
  40         case 4: // batt voltage: 1.1V, ADC6 (PA7), single-ended
  41                 ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX1);
  42                 sum_shift = 0; // 1 measurement
  43                 break;
  44         case 5: // gain stage offset: 1.1V, ADC1,1, gain 20
  45                 ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
  46                 sum_shift = 0; // 1 measurement
  47                 break;
  48         }
  49
  50         adc_sum = 0;
  51         adc_vals = 1 << sum_shift;
  52 }
  53
  54 static void start_next_adc()
  55 {
  56         if (current_adc > 0)
  57                 current_adc--;
  58         else
  59                 // TODO: kick the watchdog here.
  60                 current_adc = NUM_ADCS-1;
  61
  62         // set up mux, start one-shot conversion
  63         setup_mux(current_adc);
  64         ADCSRA |= _BV(ADSC);
  65 }
  66
  67 /*
  68  * Single synchronous ADC conversion.
  69  * Has to be called with IRQs disabled (or with the ADC IRQ disabled).
  70  */
  71 static uint16_t read_adc_sync()
  72 {
  73         uint16_t rv;
  74
  75         ADCSRA |= _BV(ADSC); // start the conversion
  76
  77         // wait for the conversion to finish
  78         while((ADCSRA & _BV(ADIF)) == 0)
  79                 ;
  80
  81         rv = ADCW;
  82         ADCSRA |= _BV(ADIF); // clear the IRQ flag
  83
  84         return rv;
  85 }
  86
  87 void init_adc()
  88 {
  89         unsigned char i;
  90         current_adc = NUM_ADCS;
  91         handler_running = 0;
  92
  93         ADCSRA = _BV(ADEN)                      // enable
  94                 | _BV(ADPS1) | _BV(ADPS0)       // CLK/8 = 125 kHz
  95                 // | _BV(ADPS2)                 // CLK/16 = 62.5 kHz
  96                 ;
  97         // ADCSRB |= _BV(GSEL); // gain 8 or 32
  98
  99         // Disable digital input on all bits used by ADC
 100         DIDR0 = _BV(ADC0D) | _BV(ADC1D) | _BV(ADC2D)
 101                 | _BV(ADC4D) | _BV(ADC5D) | _BV(ADC6D);
 102
 103         // 1.1V, ADC1,1, gain 20
 104         ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
 105
 106         /* Do first conversion and drop the result */
 107         read_adc_sync();
 108
 109         adc1_gain20_offset = 0;
 110
 111         for (i = 0; i < (1 << ADC1_GAIN20_OFFSET_SHIFT); i++) {
 112                 adc1_gain20_offset += read_adc_sync()
 113                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 114         }
 115
 116         ADCSRA |= _BV(ADIE); // enable IRQ
 117
 118         start_next_adc();
 119 }
 120
 121 void susp_adc()
 122 {
 123         ADCSRA = 0;
 124         DIDR0 = 0;
 125 }
 126
 127 ISR(ADC_vect) { // IRQ handler
 128         uint16_t adcval = ADCW;
 129
 130         if (adc_vals)
 131                 // start the next conversion immediately
 132                 ADCSRA |= _BV(ADSC);
 133
 134         if (adc_vals < (1 << sum_shift))
 135                  // drop the first conversion, use all others
 136                  adc_sum += adcval;
 137
 138         if (adc_vals) {
 139                 adc_vals--;
 140                 return;
 141         }
 142
 143         // Now handle the (1 << sum_shift) measurements
 144
 145         adcval = adc_sum >> sum_shift;
 146
 147         if (current_adc == ADC1_GAIN20) {
 148                 // running average
 149                 adc1_gain20_offset += adcval
 150                         - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 151         } else if (current_adc == 0 || current_adc == 1) {
 152                 uint16_t offset = adc1_gain20_offset
 153                         >> (ADC1_GAIN20_OFFSET_SHIFT - sum_shift);
 154                 if (adc_sum > offset)
 155                         adc_sum -= offset;
 156                 else
 157                         adc_sum = 0;
 158         }
 159
 160         if (handler_running & (1 << current_adc)) {
 161                 log_byte(0xB0 + current_adc);
 162
 163                 // drop the result, what else to do?
 164
 165                 start_next_adc();
 166         } else {
 167                 unsigned char current_adc_copy = current_adc;
 168                 uint16_t adc_sum_copy = adc_sum;
 169
 170                 start_next_adc();
 171
 172                 handler_running |= (1 << current_adc_copy);
 173                 NONATOMIC_BLOCK(NONATOMIC_FORCEOFF) {
 174                         if (current_adc_copy < N_PWMLEDS)
 175                                 pwmled_adc(current_adc_copy, adc_sum_copy);
 176                         if (current_adc_copy == AMBIENT_ADC)
 177                                 ambient_adc(adc_sum_copy);
 178                         if (current_adc_copy == BATTERY_ADC)
 179                                 battery_adc(adc_sum_copy);
 180                 }
 181                 handler_running &= ~(1 << current_adc_copy);
 182         }
 183 }
 184