borrwoed a lot code from https://github.com/foriequal0/devterm_keyboard in order to optimize the trackball

Code/devterm_keyboard/ratemeter.h

@@ -0,0 +1,38 @@
+#ifndef RATEMETER_H
+#define RATEMETER_H
+
+#include <cstdint>
+
+#include "debouncer.h"
+
+class RateMeter {
+public:
+  RateMeter();
+  void onInterrupt();
+  void tick(millis_t delta);
+  void expire();
+
+  uint16_t delta() const;
+  // Hall sensor edges per seconds.
+  // stopped: 0
+  // really slow => ~3
+  // medium => ~30
+  // fast => < 300
+  // max => 1000
+  float rate() const;
+
+private:
+  uint32_t lastTime;
+
+  // really Range, emperically:
+  // fast => < 5_000 us,
+  // medium => 20_000 - 40_000 us
+  // really slow => 250_000 us
+  uint32_t averageDelta;
+
+  static const uint16_t CUTOFF_MS = 1000;
+  // Cut off after some seconds to prevent multiple timestamp overflow (~70 mins)
+  Timeout<uint16_t, CUTOFF_MS> cutoff;
+};
+
+#endif