MT#40962 decouple RateLimit from AmAppTimer

Remove dependency on AmAppTimer's wall_clock ticks by switching to
direct call of gettimeofday() and converting the internally used time
units to milliseconds instead of the tick-based wall clock time.

Remove ::getLastUpdate() as it's unused.

Change-Id: Ia3a026103b594351c0a6943de67dd94883e30578

apps/sbc/RateLimit.cpp

@@ -1,13 +1,12 @@
 #include "RateLimit.h"
 #include "AmAppTimer.h"
+#include <sys/time.h>
 
 #define min(a,b) ((a) < (b) ? (a) : (b))
 
-DynRateLimit::DynRateLimit(unsigned int time_base_ms)
-  : last_update(0), counter(0)
+DynRateLimit::DynRateLimit(unsigned int _time_base_ms)
+  : last_update(0), counter(0), time_base_ms(_time_base_ms)
 {
-  // wall_clock has a resolution of 20ms
-  time_base = time_base_ms / 20;
 }
 
 bool DynRateLimit::limit(unsigned int rate, unsigned int peak, 
@@ -15,8 +14,8 @@ bool DynRateLimit::limit(unsigned int rate, unsigned int peak,
 {
   lock();
 
-  if(AmAppTimer::instance()->wall_clock - last_update 
-     > time_base) {
+  if(wall_clock_ms() - last_update
+     > time_base_ms) {
 
     update_limit(rate,peak);
   }
@@ -35,5 +34,12 @@ bool DynRateLimit::limit(unsigned int rate, unsigned int peak,
 void DynRateLimit::update_limit(int rate, int peak)
 {
   counter = min(peak, counter+rate);
-  last_update = AmAppTimer::instance()->wall_clock;
+  last_update = wall_clock_ms();
+}
+
+u_int32_t DynRateLimit::wall_clock_ms()
+{
+  struct timeval now;
+  gettimeofday(&now, NULL);
+  return now.tv_sec * 1000 + now.tv_usec / 1000;
 }

apps/sbc/RateLimit.h

@@ -11,7 +11,7 @@ class DynRateLimit
   u_int32_t last_update;
   int counter;
 
-  unsigned int time_base;
+  unsigned int time_base_ms;
 
   void update_limit(int rate, int peak);
 
@@ -21,7 +21,7 @@ public:
 
   virtual ~DynRateLimit() {}
 
-  unsigned int getTimeBase() const { return time_base; }
+  unsigned int getTimeBase() const { return time_base_ms * 20; /* 20 ms increments */ }
 
   /**
    * rate: units/time_base
@@ -30,8 +30,8 @@ public:
    */
   bool limit(unsigned int rate, unsigned int peak, unsigned int size);
 
-  /** Get last update timestamp (wheeltimer::wallclock ticks) */
-  u_int32_t getLastUpdate() { return last_update; }
+private:
+  static u_int32_t wall_clock_ms();
 };
 
 class RateLimit