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diff --git a/src/ticks.py b/src/ticks.py
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+from supervisor import ticks_ms
+
+# See the example at
+# https://docs.circuitpython.org/en/latest/shared-bindings/supervisor/index.html?#supervisor.ticks_ms
+_TICKS_PERIOD = const(1<<29)
+_TICKS_MAX = const(_TICKS_PERIOD-1)
+_TICKS_HALFPERIOD = const(_TICKS_PERIOD//2)
+
+def add(ticks, delta):
+    "Add a delta to a base number of ticks, performing wraparound at 2**29ms."
+    return (ticks + delta) % _TICKS_PERIOD
+
+def ticks_diff(ticks1, ticks2):
+    "Compute the signed difference between two ticks values, assuming that they are within 2**28 ticks"
+    diff = (ticks1 - ticks2) & _TICKS_MAX
+    diff = ((diff + _TICKS_HALFPERIOD) & _TICKS_MAX) - _TICKS_HALFPERIOD
+    return diff
+
+def less(ticks):
+    "Return true iff ticks1 is less than ticks2, assuming that they are within 2**28 ticks"
+    return ticks_diff(ticks_ms(), ticks) < 0