adc: measure gain stage offset _slowly_

[bike-lights.git] / firmware / adc.c

diff --git a/firmware/adc.c b/firmware/adc.c
index ba30e5ca632c01e8064323d460ce3324fa7dc23a..fa0782c4248c6ee67917901cc1340dedfefea087 100644 (file)
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -12,7 +12,8 @@ volatile static unsigned char current_adc;
 static uint16_t adc_sum;
 static unsigned char sum_shift;
 static unsigned char adc_vals;
-static uint16_t adc1_gain20_offset_x16;
+#define ADC1_GAIN20_OFFSET_SHIFT       6
+static uint16_t adc1_gain20_offset;
 
 static void inline setup_mux(unsigned char n)
 {
@@ -28,7 +29,7 @@ static void inline setup_mux(unsigned char n)
                break;
        case 2: // pwmled 3: 1.1V, ADC4 (PA5), single-ended
                ADMUX = _BV(REFS1) | _BV(MUX2);
-               sum_shift = 2; // 4 measurements
+               sum_shift = 3; // 8 measurements
                break;
        case 3: // ambient light: 1.1V, ADC5 (PA6), single-ended
                ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX0);
@@ -40,7 +41,7 @@ static void inline setup_mux(unsigned char n)
                break;
        case 5: // gain stage offset: 1.1V, ADC1,1, gain 20
                ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
-               sum_shift = 3; // 8 measurements
+               sum_shift = 0; // 1 measurement
                break;
        }
 
@@ -85,14 +86,15 @@ void init_adc()
                ;
        ADCSRA |= _BV(ADIF); // clear the IRQ flag
 
-       adc1_gain20_offset_x16 = 0;
+       adc1_gain20_offset = 0;
 
-       for (i = 0; i < 16; i++) {
+       for (i = 0; i < (1 << ADC1_GAIN20_OFFSET_SHIFT); i++) {
                ADCSRA |= _BV(ADSC);
 
                while ((ADCSRA & _BV(ADIF)) == 0)
                        ;
-               adc1_gain20_offset_x16 += ADCW;
+               adc1_gain20_offset += ADCW
+                       - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
 
                ADCSRA |= _BV(ADIF); // clear the IRQ flag
        }
@@ -128,18 +130,19 @@ ISR(ADC_vect) { // IRQ handler
 
        if (current_adc == ADC1_GAIN20) {
                // running average
-               adc1_gain20_offset_x16 += adcval
-                       - (adc1_gain20_offset_x16 >> 4);
+               adc1_gain20_offset += adcval
+                       - (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
        } else if (current_adc == 0 || current_adc == 1) {
-               uint16_t offset = adc1_gain20_offset_x16 >> 4;
-               if (adcval >= offset)
-                       adcval -= offset;
+               uint16_t offset = adc1_gain20_offset
+                       >> (ADC1_GAIN20_OFFSET_SHIFT - sum_shift);
+               if (adc_sum > offset)
+                       adc_sum -= offset;
                else
-                       adcval = 0;
+                       adc_sum = 0;
        }
 
        if (current_adc < N_PWMLEDS)
-               pwmled_adc(current_adc, adcval);
+               pwmled_adc(current_adc, adc_sum);
        if (current_adc == AMBIENT_ADC)
                ambient_adc(adcval);
        if (current_adc == BATTERY_ADC)
@@ -152,7 +155,9 @@ void timer_start_adcs()
 {
        if (current_adc == NUM_ADCS) // Don't start if in progress
                start_next_adc();
+#if 0
        else
                log_byte(0x99);
+#endif
 }