GeorgeWort · GeorgeWort · Jul 9, 2019
diff --git a/inc/core/MicroBitComponent.h b/inc/core/MicroBitComponent.h
@@ -35,6 +35,7 @@ DEALINGS IN THE SOFTWARE.
 #define MICROBIT_ID_ACCELEROMETER       4
 #define MICROBIT_ID_COMPASS             5
 #define MICROBIT_ID_DISPLAY             6
+#define MICROBIT_ID_LIGHT_SENSOR        7
 
 //EDGE connector events
 #define MICROBIT_IO_PINS                20

diff --git a/inc/drivers/MicroBitDisplay.h b/inc/drivers/MicroBitDisplay.h
@@ -627,13 +627,17 @@ class MicroBitDisplay : public MicroBitComponent
       * This also changes the tickPeriod to MICROBIT_LIGHT_SENSOR_TICK_SPEED so
       * that the display does not suffer from artifacts.
       *
+      * @param valid_only True to return -1 if full set of results not taken and to return a stale
+      *            but valid reading in the case of invalid results. False to use all results.
+      *            Defaults to microbitMatrixMap, defined in MicroBitMatrixMaps.h.
+      *
       * @return an indicative light level in the range 0 - 255.
       *
       * @note this will return 0 on the first call to this method, a light reading
       * will be available after the display has activated the light sensor for the
       * first time.
       */
-    int readLightLevel();
+    int readLightLevel(bool valid_only = false);
 
     /**
       * Destructor for MicroBitDisplay, where we deregister this instance from the array of system components.

diff --git a/inc/drivers/MicroBitLightSensor.h b/inc/drivers/MicroBitLightSensor.h
@@ -32,12 +32,17 @@ DEALINGS IN THE SOFTWARE.
 #include "EventModel.h"
 #include "MicroBitMatrixMaps.h"
 
-#define MICROBIT_LIGHT_SENSOR_CHAN_NUM      3
-#define MICROBIT_LIGHT_SENSOR_AN_SET_TIME   4000
-#define MICROBIT_LIGHT_SENSOR_TICK_PERIOD   5
+/**
+  * Event codes raised by MicroBitDisplay
+  */
+#define MICROBIT_DISPLAY_EVT_LIGHT_SENSE_READY   1
+
+#define MICROBIT_LIGHT_SENSOR_CHAN_NUM           3
+#define MICROBIT_LIGHT_SENSOR_AN_SET_TIME        4000
+#define MICROBIT_LIGHT_SENSOR_TICK_PERIOD        5
 
-#define MICROBIT_LIGHT_SENSOR_MAX_VALUE     338
-#define MICROBIT_LIGHT_SENSOR_MIN_VALUE     75
+#define MICROBIT_LIGHT_SENSOR_MAX_VALUE          338
+#define MICROBIT_LIGHT_SENSOR_MIN_VALUE          75
 
 /**
   * Class definition for MicroBitLightSensor.
@@ -50,6 +55,12 @@ class MicroBitLightSensor
     //contains the results from each section of the display
     int results[MICROBIT_LIGHT_SENSOR_CHAN_NUM];
 
+    // The average of the three results.
+    int average;
+
+    // The average of the three results the last time all results were valid.
+    int valid_average;
+
     //holds the current channel (also used to index the results array)
     uint8_t chan;
 
@@ -81,6 +92,15 @@ class MicroBitLightSensor
       */
     void analogDisable();
 
+    /**
+      * This method updates the average of the three results, as well as the valid_average
+      * if results are valid. The MICROBIT_DISPLAY_EVT_LIGHT_SENSE_READY event is sent if
+      * the valid_average is updated.
+      *
+      * @return returns a boolean representing whether or not the results are valid.
+      */
+    bool update_averages();
+
     public:
 
     /**
@@ -111,10 +131,14 @@ class MicroBitLightSensor
       *
       * Where each number represents a different section on the 5 x 5 matrix display.
       *
+      * @param valid_only True to return -1 if full set of results not taken and to return a stale
+      *            but valid reading in the case of invalid results. False to use all results.
+      *            Defaults to microbitMatrixMap, defined in MicroBitMatrixMaps.h.
+      *
       * @return returns a value in the range 0 - 255 where 0 is dark, and 255
       * is very bright
       */
-    int read();
+    int read(bool valid_only = false);
 
     /**
       * The method that is invoked by sending MICROBIT_DISPLAY_EVT_LIGHT_SENSE

diff --git a/source/drivers/MicroBitDisplay.cpp b/source/drivers/MicroBitDisplay.cpp
@@ -1210,21 +1210,25 @@ MicroBitImage MicroBitDisplay::screenShot()
   * This also changes the tickPeriod to MICROBIT_LIGHT_SENSOR_TICK_SPEED so
   * that the display does not suffer from artifacts.
   *
+  * @param valid_only True to return -1 if full set of results not taken and to return a stale
+  *            but valid reading in the case of invalid results. False to use all results.
+  *            Defaults to microbitMatrixMap, defined in MicroBitMatrixMaps.h.
+  *
   * @return an indicative light level in the range 0 - 255.
   *
-  * @note this will return 0 on the first call to this method, a light reading
-  * will be available after the display has activated the light sensor for the
-  * first time.
+  * @note this will return 255 (previously said 0, which was incorrect)
+  * on the first call to this method, a light reading will be available
+  * after the display has activated the light sensor for the first time.
   */
-int MicroBitDisplay::readLightLevel()
+int MicroBitDisplay::readLightLevel(bool valid_only)
 {
     if(mode != DISPLAY_MODE_BLACK_AND_WHITE_LIGHT_SENSE)
     {
         setDisplayMode(DISPLAY_MODE_BLACK_AND_WHITE_LIGHT_SENSE);
         this->lightSensor = new MicroBitLightSensor(matrixMap);
     }
 
-    return this->lightSensor->read();
+    return this->lightSensor->read(valid_only);
 }
 
 /**

diff --git a/source/drivers/MicroBitLightSensor.cpp b/source/drivers/MicroBitLightSensor.cpp
@@ -51,6 +51,8 @@ void MicroBitLightSensor::analogReady()
     chan++;
 
     chan = chan % MICROBIT_LIGHT_SENSOR_CHAN_NUM;
+
+    update_averages();
 }
 
 /**
@@ -87,15 +89,43 @@ MicroBitLightSensor::MicroBitLightSensor(const MatrixMap &map) :
 {
     this->chan = 0;
 
+    valid_average = -1;
+
     for(int i = 0; i < MICROBIT_LIGHT_SENSOR_CHAN_NUM; i++)
-        results[i] = 0;
+        results[i] = -1;
 
     if (EventModel::defaultEventBus)
         EventModel::defaultEventBus->listen(MICROBIT_ID_DISPLAY, MICROBIT_DISPLAY_EVT_LIGHT_SENSE, this, &MicroBitLightSensor::startSensing, MESSAGE_BUS_LISTENER_IMMEDIATE);
 
     this->sensePin = NULL;
 }
 
+/**
+  * This method updates the average of the three results, as well as the valid_average
+  * if results are valid. The MICROBIT_DISPLAY_EVT_LIGHT_SENSE_READY event is sent if
+  * the valid_average is updated.
+  *
+  * @return returns a boolean representing whether or not the results are valid.
+  */
+bool MicroBitLightSensor::update_averages()
+{
+    bool valid = true;
+    int sum = 0;
+    for(int i = 0; i < MICROBIT_LIGHT_SENSOR_CHAN_NUM; i++) {
+        if (this->results[i] < 0 || this->results[i] > 450) {
+            valid = false;
+        }
+        // Use zero if a result hasn't been used rather than -1.
+        sum += max(this->results[i], 0);
+    }
+    this->average = sum / MICROBIT_LIGHT_SENSOR_CHAN_NUM;
+    if (valid) {
+        this->valid_average = this->average;
+        MicroBitEvent(MICROBIT_ID_LIGHT_SENSOR, MICROBIT_DISPLAY_EVT_LIGHT_SENSE_READY);
+    }
+    return valid;
+}
+
 /**
   * This method returns a summed average of the three sections of the display.
   *
@@ -114,17 +144,19 @@ MicroBitLightSensor::MicroBitLightSensor(const MatrixMap &map) :
   *
   * Where each number represents a different section on the 5 x 5 matrix display.
   *
+  * @param valid_only True to return -1 if full set of results not taken and to return a stale
+  *            but valid reading in the case of invalid results. False to use all results.
+  *            Defaults to microbitMatrixMap, defined in MicroBitMatrixMaps.h.
+  *
   * @return returns a value in the range 0 - 255 where 0 is dark, and 255
   * is very bright
   */
-int MicroBitLightSensor::read()
+int MicroBitLightSensor::read(bool valid_only)
 {
-    int sum = 0;
-
-    for(int i = 0; i < MICROBIT_LIGHT_SENSOR_CHAN_NUM; i++)
-        sum += results[i];
+    int average = valid_only ? this->valid_average : this->average;
 
-    int average = sum / MICROBIT_LIGHT_SENSOR_CHAN_NUM;
+    if (valid_only && average < 0)
+        return -1;
 
     average = min(average, MICROBIT_LIGHT_SENSOR_MAX_VALUE);