adc.c: routine for synchronous conversion

diff --git a/firmware/adc.c b/firmware/adc.c
index f5d846f2b21d0340bd8f3411a1d214db5ae04583..abbd3bac5b93c90c2ad9304b0430165e32aa3805 100644 (file)
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -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