X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?a=blobdiff_plain;f=firmware%2Fadc.c;h=6ef638a5c79204f20251608db63371bfd51a3fc6;hb=9e483c6969d2cdce60f6dcc3d167fec889a48993;hp=f5d846f2b21d0340bd8f3411a1d214db5ae04583;hpb=dfdde30a343b7da032bea880b0677b49ff0e5d8a;p=bike-lights.git

diff --git a/firmware/adc.c b/firmware/adc.c
index f5d846f..6ef638a 100644
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -33,7 +33,7 @@ static void inline setup_mux(unsigned char n)
 		break;
 	case 3: // ambient light: 1.1V, ADC5 (PA6), single-ended
 		ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX0);
-		sum_shift = 0; // 1 measurement
+		sum_shift = 3; // 3 measurements
 		break;
 	case 4: // batt voltage: 1.1V, ADC6 (PA7), single-ended
 		ADMUX = _BV(REFS1) | _BV(MUX2) | _BV(MUX1);
@@ -62,6 +62,26 @@ static void start_next_adc()
 	ADCSRA |= _BV(ADSC);
 }
 
+/*
+ * Single synchronous ADC conversion.
+ * Has to be called with IRQs disabled (or with the ADC IRQ disabled).
+ */
+static uint16_t read_adc_sync()
+{
+	uint16_t rv;
+
+	ADCSRA |= _BV(ADSC); // start the conversion
+
+	// wait for the conversion to finish
+	while((ADCSRA & _BV(ADIF)) == 0)
+		;
+
+	rv = ADCW;
+	ADCSRA |= _BV(ADIF); // clear the IRQ flag
+
+	return rv;
+}
+
 void init_adc()
 {
 	unsigned char i;
@@ -79,24 +99,15 @@ void init_adc()
 
 	// 1.1V, ADC1,1, gain 20
 	ADMUX = _BV(REFS1) | _BV(MUX3) | _BV(MUX2) | _BV(MUX0);
-	ADCSRA |= _BV(ADSC);
 
 	/* Do first conversion and drop the result */
-	while ((ADCSRA & _BV(ADIF)) == 0)
-		;
-	ADCSRA |= _BV(ADIF); // clear the IRQ flag
+	read_adc_sync();
 
 	adc1_gain20_offset = 0;
 
 	for (i = 0; i < (1 << ADC1_GAIN20_OFFSET_SHIFT); i++) {
-		ADCSRA |= _BV(ADSC);
-
-		while ((ADCSRA & _BV(ADIF)) == 0)
-			;
-		adc1_gain20_offset += ADCW
+		adc1_gain20_offset += read_adc_sync()
 			- (adc1_gain20_offset >> ADC1_GAIN20_OFFSET_SHIFT);
-
-		ADCSRA |= _BV(ADIF); // clear the IRQ flag
 	}
 
 	ADCSRA |= _BV(ADIE); // enable IRQ