more work on analog system, still untested

analog.c

@@ -1,17 +1,54 @@
 #include "analog.h"
 
+#include	<avr/interrupt.h>
+
 #include	"arduino.h"
+#include	"machine.h"
+
+#ifndef	ANALOG_MASK
+	#warning	define ANALOG_MASK as a bitmask of all the analog channels you wish to use
+	#error		ANALOG_MASK not defined
+#endif
+
+uint8_t adc_running_mask, adc_counter;
+
+volatile uint16_t adc_result[8] __attribute__ ((section ".bss"));
 
 void analog_init() {
+	#if ANALOG_MASK > 0
 	PRR &= ~MASK(PRADC);
 	ADMUX = REFERENCE;
+	// ADC frequency must be less than 200khz or we lose precision. At 16MHz system clock, we must use the full prescale value of 128 to get an ADC clock of 125khz.
 	ADCSRA = MASK(ADEN) | MASK(ADPS2) | MASK(ADPS1) | MASK(ADPS0);
+
+	adc_counter = 0;
+	adc_running_mask = 1;
+
+	DIDR0 = ANALOG_MASK & 0x1F;
+
+	// now we start the first conversion and leave the rest to the interrupt
+	ADCSRA |= MASK(ADIE) | MASK(ADSC);
+	#endif
+}
+
+ISR(ADC_vect) {
+	// emulate free-running mode but be more deterministic about exactly which result we have, since this project has long-running interrupts
+	adc_result[ADMUX & 0x0F] = ADC;
+	// find next channel
+	do {
+		adc_counter++;
+		adc_running_mask <<= 1;
+		if (adc_counter == 8) {
+			adc_counter = 0;
+			adc_running_mask = 1;
+		}
+	} while ((adc_running_mask & ANALOG_MASK) == 0);
+
+	// start next conversion
+	ADMUX = (adc_counter) | REFERENCE;
+	ADCSRA |= MASK(ADSC);
 }
 
 uint16_t	analog_read(uint8_t channel) {
-	ADMUX = (ADMUX & 0xF0) | channel;
+	return adc_result[channel];
-	ADCSRA |= MASK(ADSC);
-	// FIXME: waits. I hate waiting.
-	for (;ADCSRA | MASK(ADSC););
-	return ADC;
 }