AP_Compass: move responsibility for logging into library

libraries/AP_Compass/AP_Compass.cpp

@@ -981,7 +981,11 @@ Compass::read(void)
     if (_learn == LEARN_INFLIGHT && learn != nullptr) {
         learn->update();
     }
-    return healthy();
+    bool ret = healthy();
+    if (ret && _log_bit != (uint32_t)-1 && AP::logger().should_log(_log_bit) && !AP::ahrs().have_ekf_logging()) {
+        AP::logger().Write_Compass();
+    }
+    return ret;
 }
 
 uint8_t

libraries/AP_Compass/AP_Compass.h

@@ -143,6 +143,9 @@ public:
     bool compass_cal_requires_reboot() const { return _cal_complete_requires_reboot; }
     bool is_calibrating() const;
 
+    // indicate which bit in LOG_BITMASK indicates we should log compass readings
+    void set_log_bit(uint32_t log_bit) { _log_bit = log_bit; }
+
     /*
       handle an incoming MAG_CAL command
     */
@@ -404,6 +407,9 @@ private:
     // first-time-around flag used by offset nulling
     bool        _null_init_done;
 
+    // stores which bit is used to indicate we should log compass readings
+    uint32_t _log_bit = -1;
+
     // used by offset correction
     static const uint8_t _mag_history_size = 20;