Add Trigger class.

Makefile

@@ -6,6 +6,7 @@ SOURCES :=					\
 		include/feather/feather_m0.h	\
 		include/feather/feather_m4.h	\
 		include/feather/scheduling.h	\
+		include/feather/trigger.h	\
 		include/feather/util.h		\
 		include/feather/wing/adalogger.h\
 		include/feather/wing/gps.h	\
@@ -16,6 +17,7 @@ SOURCES :=					\
 		src/button.cc			\
 		src/feather_m0.cc		\
 		src/feather_m4.cc		\
+		src/trigger.cc			\
 		src/util.cc			\
 		src/wing_adalogger.cc		\
 		src/wing.cc			\

include/feather/trigger.h

@@ -0,0 +1,19 @@
+#ifndef __FEATHERLIB_TRIGGER_H
+#define __FEATHERLIB_TRIGGER_H
+
+
+// A Trigger returns true if enough time has passed.
+class Trigger {
+public:
+	Trigger(unsigned long delta) : next(0), delta(delta) {}
+	Trigger(unsigned long delta, bool skipFirst);
+	bool ready();
+	bool ready(unsigned long now);
+
+private:
+	unsigned long	next;
+	unsigned long	delta;
+};
+
+
+#endif // __FEATHERLIB_TRIGGER_H

src/trigger.cc

@@ -0,0 +1,32 @@
+#include <Arduino.h>
+
+#include <feather/trigger.h>
+
+
+Trigger::Trigger(unsigned long delta, bool skipFirst)
+{
+	this->next = 0;
+	this->delta = delta;
+	if (skipFirst) {
+		this->next = millis() + delta;
+	}
+}
+
+
+bool
+Trigger::ready()
+{
+	return this->ready(millis());
+}
+
+
+bool
+Trigger::ready(unsigned long now)
+{
+	if (this->next < now) {
+		this->next = now + this->delta;
+		return true;
+	}
+
+	return false;
+}