example code showing use of dmpSetFIFOPacketSize when MCU is powercyc…

…led or goes into deep sleep but MPU6050 remains active

examples/MCU_Powercycle_DMP6/MCU_Powercycle_DMP6.ino

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+// This sample code shows how to use dmpSetFIFOPacketSize() so as not to waste time
+// initializaing the MPU6050 when the MCU has been reset or powercycled but the MPU6050 has not.
+// Instead we just need to set the FIFOPacketSize, since this is the only setting needed
+// that was stored in the MCU RAM.
+
+// This example code was written for the LGT8F328. In this example the LGT8F328 goes into
+// a deep sleep for 1 second which erases its ram and thus causes the MCU to restart on wakeup.
+// The code is based off a simplication of example code "MPU6050_DMP6".
+
+// Code and comments related to demonstrating how to use dmpSetFIFOPacketSize() are preceded
+// by a line of asterisks (***************************************************************).
+
+#include "I2Cdev.h"
+#include "MPU6050_6Axis_MotionApps20.h"
+#include <lgt_LowPower.h>
+
+#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
+#include "Wire.h"
+#endif
+
+MPU6050 mpu;
+
+// MPU control/status vars
+uint8_t devStatus;       // return status after each device operation (0 = success, !0 = error)
+uint16_t packetSize;     // expected DMP packet size (default is 42 bytes)
+uint8_t fifoBuffer[42];  // FIFO storage buffer
+
+// orientation/motion vars
+Quaternion q;         // [w, x, y, z]         quaternion container
+VectorFloat gravity;  // [x, y, z]            gravity vector
+float ypr[3];         // [yaw, pitch, roll]   yaw/pitch/roll container and gravity vector
+uint32_t startTime;
+
+// ================================================================
+// ===                      INITIAL SETUP                       ===
+// ================================================================
+
+void setup() {
+// join I2C bus (I2Cdev library doesn't do this automatically)
+#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
+  Wire.begin();
+  Wire.setClock(400000);  // 400kHz I2C clock. Comment this line if having compilation difficulties
+#elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
+  Fastwire::setup(400, true);
+#endif
+
+  Serial.begin(115200);
+  Serial.println(F("Starting setup"));
+
+  // ***************************************************************
+  // if MotionDetectionDuration is not the default value (0) but is instead a value we have set previously (1)
+  // then we know that the mpu6050 has not been reset or powercycled only the MCU has been, so we don't need
+  // to waste time reininitializing the mpu6050. Instead we just have to set the MCU to know the packet size
+  // since this value was only retained previously in the MCU RAM:
+  if (mpu.getMotionDetectionDuration() == 1) {
+    Serial.println("Skipping MPU6050 initialization");
+    mpu.dmpSetFIFOPacketSize(42);
+    return;
+  }
+
+  // ***************************************************************
+  // if we got here then the MPU6050 has been power cycled or reset so we have to do a full initialization
+  Serial.println(F("Initializing I2C devices..."));
+  mpu.initialize();
+
+  // verify connection
+  Serial.println(F("Testing device connections..."));
+  Serial.println(mpu.testConnection() ? F("MPU6050 connection successful") : F("MPU6050 connection failed"));
+
+  // load and configure the DMP
+  Serial.println(F("Initializing DMP..."));
+  devStatus = mpu.dmpInitialize();
+
+  // make sure it worked (returns 0 if so)
+  if (devStatus == 0) {
+    // Calibration Time: generate offsets and calibrate our MPU6050
+    mpu.CalibrateAccel(6);
+    mpu.CalibrateGyro(6);
+    Serial.println(F("Enabling DMP..."));
+    mpu.setDMPEnabled(true);
+
+    // get expected DMP packet size for later comparison
+    packetSize = mpu.dmpGetFIFOPacketSize();
+  } else {
+    // ERROR!
+    // 1 = initial memory load failed
+    // 2 = DMP configuration updates failed
+    // (if it's going to break, usually the code will be 1)
+    Serial.print(F("DMP Initialization failed (code "));
+    Serial.print(devStatus);
+    Serial.println(F(")"));
+  }
+
+  // ***************************************************************
+  // set MotionDetectionDuration to a value other than the default (0).
+  // Note that we could set any value other than default in the MPU6050
+  // and test for that instead of MotionDetectionDuration. We chose
+  // MotionDetectionDuration to set in this example only as an example
+  // of how to test for reset/powerup on the MPU6050.
+  mpu.setMotionDetectionDuration(1);
+
+  startTime = millis();
+}
+
+
+
+// ================================================================
+// ===                    MAIN PROGRAM LOOP                     ===
+// ================================================================
+
+void loop() {
+  if ((millis() - startTime) < 5000) { // show YPR values for 5 seconds
+    if (mpu.dmpGetCurrentFIFOPacket(fifoBuffer)) {  // Get the Latest packet
+      // display Euler angles in degrees
+      mpu.dmpGetQuaternion(&q, fifoBuffer);
+      mpu.dmpGetGravity(&gravity, &q);
+      mpu.dmpGetYawPitchRoll(ypr, &q, &gravity);
+      Serial.print("ypr\t");
+      Serial.print(ypr[0] * 180 / M_PI);
+      Serial.print("\t");
+      Serial.print(ypr[1] * 180 / M_PI);
+      Serial.print("\t");
+      Serial.println(ypr[2] * 180 / M_PI);
+    }
+  } else {
+    // ***************************************************************
+    // 5 seconds have passed
+    // put the MCU into a deep sleep for 1 second. All RAM is lost
+    // however the MPU6050 will continue to operate.
+    Serial.println("going to sleep for 1 Sec.");
+    delay(100); // give the MCU a chance to print the above message
+    LowPower.deepSleep2(SLEEP_1S);
+  }
+}