AP_NavEKF2: make it easy to do EK2 timing tests

for future benchmarking

libraries/AP_NavEKF2/AP_NavEKF2_core.cpp

@@ -19,6 +19,20 @@ extern const AP_HAL::HAL& hal;
 // maximum allowed gyro bias (rad/sec)
 #define GYRO_BIAS_LIMIT 0.5f
 
+/*
+  to run EK2 timing tests you need to set ENABLE_EKF_TIMING to 1, plus setup as follows:
+    - copter at 400Hz
+    - INS_FAST_SAMPLE=0
+    - EKF2_MAG_CAL=4
+    - GPS_TYPE=14
+    - load fakegps in mavproxy
+    - ensure a compass is enabled
+    - wait till EK2 reports "using GPS" (this is important, ignore earlier results)
+
+    DO NOT FLY WITH THIS ENABLED
+ */
+#define ENABLE_EKF_TIMING 0
+
 // constructor
 NavEKF2_core::NavEKF2_core(NavEKF2 *_frontend) :
     _perf_UpdateFilter(hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, "EK2_UpdateFilter")),
@@ -534,8 +548,10 @@ void NavEKF2_core::UpdateFilter(bool predict)
     }
 
     // start the timer used for load measurement
-#if EK2_DISABLE_INTERRUPTS
+#if ENABLE_EKF_TIMING
     void *istate = hal.scheduler->disable_interrupts_save();
+    static uint32_t timing_start_us;
+    timing_start_us = AP_HAL::micros();
 #endif
     hal.util->perf_begin(_perf_UpdateFilter);
 
@@ -585,7 +601,15 @@ void NavEKF2_core::UpdateFilter(bool predict)
 
     // stop the timer used for load measurement
     hal.util->perf_end(_perf_UpdateFilter);
-#if EK2_DISABLE_INTERRUPTS
+#if ENABLE_EKF_TIMING
+    static uint32_t total_us;
+    static uint32_t timing_counter;
+    total_us += AP_HAL::micros() - timing_start_us;
+    if (timing_counter++ == 4000) {
+        hal.console->printf("ekf2 avg %.2f us\n", total_us / float(timing_counter));
+        total_us = 0;
+        timing_counter = 0;
+    }
     hal.scheduler->restore_interrupts(istate);
 #endif