fix tick overflow and implement periodic timer class.

kmk/kmktime.py

@@ -1,4 +1,5 @@
 from micropython import const
+from supervisor import ticks_ms
 
 _TICKS_PERIOD = const(1 << 29)
 _TICKS_MAX = const(_TICKS_PERIOD - 1)
@@ -13,3 +14,17 @@ def ticks_diff(new, start):
 
 def check_deadline(new, start, ms):
     return ticks_diff(new, start) < ms
+
+
+class PeriodicTimer:
+    def __init__(self, period):
+        self.period = period
+        self.last_tick = ticks_ms()
+
+    def tick(self):
+        now = ticks_ms()
+        if ticks_diff(now, self.last_tick) >= self.period:
+            self.last_tick = now
+            return True
+        else:
+            return False