fw: Implement power-on battery check

firmware/batmon.c

@@ -33,15 +33,14 @@ uint8_t batmon_proc()
 
 	if (ADCSRA & (1 << ADIF)) {
 		sum += ADCH;
-		if (!(cnt++)) {
+		if (!(++cnt)) {
 			vbat = sum >> 8;
 			sum = 0;
+			if (vbat < BAT_THRES_POWER_OFF)
+				return 1;
 		}
-		vbat = ADCH;
 		ADCSRA &= ~(1 << ADIF);
 		ADCSRA |= (1 << ADSC); // TODO: I want this to work off TIMER0
-		if (vbat < BAT_THRES_POWER_OFF)
-			return 1;
 	}
 	return 0;
 }
@@ -50,3 +49,28 @@ inline uint8_t batmon_get_voltage()
 {
 	return vbat;
 }
+
+static uint8_t batmon_get_voltage_sync()
+{
+	uint16_t sum = 0;
+	uint8_t cnt = 255;
+
+	ADCSRA |= (1 << ADSC);
+
+	do {
+		if (ADCSRA & (1 << ADIF)) {
+			sum += ADCH;
+			ADCSRA &= ~(1 << ADIF);
+			ADCSRA |= (1 << ADSC);
+			cnt--;
+		}
+	} while (cnt);
+
+	return (sum >> 8);
+}
+
+// Note: Call batmon_init() after using this function before using batmon_proc() again
+inline uint8_t batmon_ok_to_boot()
+{
+	return (batmon_get_voltage_sync() > BAT_THRES_POWER_ON);
+}

firmware/batmon.h

@@ -12,5 +12,6 @@
 void batmon_init();
 uint8_t batmon_get_voltage();
 uint8_t batmon_proc();
+uint8_t batmon_ok_to_boot();
 
 #endif // BATMON_H

firmware/main.c

@@ -88,6 +88,7 @@ int main()
 	MCUSR &= ~(1 << WDRF);
 	WDTCSR = (1 << WDCE);
 	cli();
+	_delay_ms(25);
 
 	suspend();
 

firmware/pm.c

@@ -4,6 +4,7 @@
 #include <avr/interrupt.h>
 #include <avr/pgmspace.h>
 #include "pm.h"
+#include "batmon.h"
 
 static void disable_periphery()
 {
@@ -58,7 +59,10 @@ void reset()
 
 char* post()
 {
-	// TODO: Implement battery voltage check
 	_delay_ms(500);
+
+	if (!batmon_ok_to_boot())
+		return PSTR("Low battery.");
+
 	return 0;
 }