adc.c: abort the current reading when the timer expires

Inside the timer interrupt, we may have changed the PWM outputs,
so the reading of ADC will be useless. Drop it in this case.

FIXME: possible race condition against timer IRQ.

diff --git a/firmware/adc.c b/firmware/adc.c
index 9ed80f2d216b069412a2a12a53444c048d8a57eb..5ebc0a6d0d6076d224c594441773298ff48d6939 100644 (file)
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -204,6 +204,18 @@ static void adc1_gain20_adc(uint16_t adcsum)
 ISR(ADC_vect) { // IRQ handler
        uint16_t adcval = ADCW;
 
+       /*
+        * After the timer interrupt, drop the current reading.
+        * We may have changed the PWM outputs, so the value is
+        * probably useless anyway.
+        * FIXME: possible race condition - we should make an explicit
+        * notification inside the timer IRQ handler.
+        */
+       if (slow_adcs_wanted) {
+               start_next_adc();
+               return;
+       }
+
        if (zero_count) {
                if (zero_count > 1) {
                        ADCSRA |= _BV(ADSC);