v4 LED - Wait for LLv4LED to acknowledge GPIO cmd

After toggling trigger pin, wait for LLv4 to acknowledge receipt of
command before moving on. Otherwise, we could falsely detect 'not-busy'
if we check for busy via GPIO too quickly.

Change-Id: I7447f79e7a91a8a2c5e38afb0a6bec7851094d82

examples/v4LED/v4LED_I2C/v4LED_I2C.ino

@@ -252,7 +252,7 @@ uint8_t distanceSingle(uint16_t * distance)
 uint8_t distanceSingleGpio(uint16_t * distance)
 {
     // 1. Trigger range measurement.
-    myLidarLite.takeRangeGpio(TriggerPin);
+    myLidarLite.takeRangeGpio(TriggerPin, MonitorPin);
 
     // 2. Wait for busyFlag to indicate device is idle.
     myLidarLite.waitForBusyGpio(MonitorPin);
@@ -315,7 +315,7 @@ uint8_t distanceContinuousGpio(uint16_t * distance)
     if (myLidarLite.getBusyFlagGpio(MonitorPin) == 0)
     {
         // Trigger the next range measurement
-        myLidarLite.takeRangeGpio(TriggerPin);
+        myLidarLite.takeRangeGpio(TriggerPin, MonitorPin);
 
         // Read new distance data from device registers
         *distance = myLidarLite.readDistance();

src/LIDARLite_v4LED.cpp

@@ -199,13 +199,23 @@ uint8_t LIDARLite_v4LED::getBusyFlag(uint8_t lidarliteAddress)
   Parameters
   ------------------------------------------------------------------------------
   triggerPin: digital output pin connected to trigger input of LIDAR-Lite
+  monitorPin: digital input pin connected to monitor output of LIDAR-Lite
 ------------------------------------------------------------------------------*/
-void LIDARLite_v4LED::takeRangeGpio(uint8_t triggerPin)
+void LIDARLite_v4LED::takeRangeGpio(uint8_t triggerPin, uint8_t monitorPin)
 {
+    uint8_t busyFlag;
+
     if (digitalRead(triggerPin))
         digitalWrite(triggerPin, LOW);
     else
         digitalWrite(triggerPin, HIGH);
+
+    // When LLv4 receives trigger command it will drive monitor pin low.
+    // Wait for LLv4 to acknowledge receipt of command before moving on.
+    do
+    {
+        busyFlag = getBusyFlagGpio(monitorPin);
+    } while (!busyFlag);
 } /* LIDARLite_v4LED::takeRangeGpio */
 
 /*------------------------------------------------------------------------------
@@ -395,4 +405,3 @@ void LIDARLite_v4LED::correlationRecordRead(
         correlationArray[i] = correlationValue;
     }
 } /* LIDARLite_v4LED::correlationRecordRead */
-

src/LIDARLite_v4LED.h

@@ -42,7 +42,7 @@ class LIDARLite_v4LED
       void      takeRange   (uint8_t lidarliteAddress = LIDARLITE_ADDR_DEFAULT);
       void      waitForBusyGpio (uint8_t monitorPin);
       uint8_t   getBusyFlagGpio (uint8_t monitorPin);
-      void      takeRangeGpio   (uint8_t triggerPin);
+      void      takeRangeGpio   (uint8_t triggerPin, uint8_t monitorPin);
 
       void      write (uint8_t regAddr, uint8_t * dataBytes, uint8_t numBytes, uint8_t lidarliteAddress = LIDARLITE_ADDR_DEFAULT);
       void      read  (uint8_t regAddr, uint8_t * dataBytes, uint8_t numBytes, uint8_t lidarliteAddress = LIDARLITE_ADDR_DEFAULT);