unify periodic timers

src/Periodic.h

@@ -1,32 +1,22 @@
 #pragma once
 
 #include <Arduino.h>
+#include "PeriodicTask.h"
 
 /**
  * Periodically invoke a callback.
  * 
- * FIXME: currently just syntatic sugar for polling in loop (you must call .loop), but eventually
- * generalize with the freertos scheduler so we can save lots of power by having everything either in
- * something like this or triggered off of an irq.
+ * This just provides C style callback conventions rather than a virtual function - FIXME, remove?
  */
-class Periodic
+class Periodic : public PeriodicTask
 {
-  uint32_t lastMsec = 0;
-  uint32_t period = 1; // call soon after creation
   uint32_t (*callback)();
 
 public:
   // callback returns the period for the next callback invocation (or 0 if we should no longer be called)
   Periodic(uint32_t (*_callback)()) : callback(_callback) {}
 
-  // for the time being this must be called from loop
-  void loop()
-  {
-    uint32_t now = millis();
-    if (period && (now - lastMsec) >= period)
-    {
-      lastMsec = now;
-      period = (*callback)();
-    }
-  }
+protected:
+
+  uint32_t doTask();
 };