Clean up timer interface

explicitly initialize the timer,
don't pass the value around every time

timer.c

@@ -54,15 +54,28 @@ static uint8_t nsub = SUB;
 #endif
 
 /* return True every MS milliseconds */
-char every(int16_t sec, timer_t *t)
+char timer_done(timer_t *t)
 {
-	if((current-t->current) >= 0) {
-		t->current += sec;
+	if((current - t->last) >= 0)
 		return 1;
-	}
 	return 0;
 }
 
+int16_t timer_remaining(timer_t *t)
+{
+	return t->last-current;
+}
+
+void timer_start(int16_t sec, timer_t *t)
+{
+	t->last += sec;
+}
+
+void timer_reset(timer_t *t)
+{
+	t->last = current;
+}
+
 void timer_init(void)
 {
 	TCCR0A=0;

timer.h

@@ -7,11 +7,27 @@
 #if defined(HAVE_TIMER)
 
 typedef struct {
-	int16_t current;
+	int16_t last;
 } timer_t;
 
-/* return True every S seconds */
-char every(int16_t sec, timer_t *t);
+/* return True every sec tenth seconds */
+char timer_done(timer_t *t);
+void timer_start(int16_t sec, timer_t *t);
+int16_t timer_remaining(timer_t *t);
+
+void timer_reset(timer_t *t);
+
+/**
+ * The point of 'reset_delta' is: assume every(20,&t) controls a 50% PWM output
+ * and is called half a second too late at the end of the 'off' phase. You have 
+ * three choices:
+ * = do nothing: the 'on' phase will last 1.5 seconds, thus the next on>off
+ *   transition isn't delayed.
+ * = call reset(): 'on' will be 2.0 seconds, thus keeping individual timing
+ *   as accurately aspossible
+ * = call reset_delta(20,&t): 'on' will be 2.5 seconds, thereby making sure
+ *   that the on/off ratio isn't disturbed too much.
+ */
 
 void timer_init(void);
 void timer_poll(void);