This is a Teensy 3.2 program to monitor I2C transactions between an I2C master and an I2C slave device. As it stands, the program is 
specialized for a MPU6050 I2C device, and prints out the calculated yaw value each time it detects a 28-bit packet from the MPU6050 DMP.
It was created using Visual Studio 2019 and the Visual Micro add-in for Arduino.

/* 'Notes:

    A typical I2C sentence when communicating with a MPU6050 IMU module goes something like:
        "I2C(68) wrote 1 byte to 75 - C0 Done."
        "I2C(68) wrote 3 bytes to 72 - C0 0C 10 Done."
        "I2C(68) read 5 bytes from 6A - C0 0C 10 14 03 Done."

    To form a sentence, we need:
        Device addr: 68 in the above examples
        Read/Write direction
        To/From register address:  75, 72 and 6A in the above examples
        Data:  C0, C0 0C 10, and C0 0C 10 14 03 in the above examples
        number of bytes written/read:  1,3 & 5 in the above examples

     Each I2C communication proceeds as follows (assuming a START from an IDLE condition):
         A START or RESTART condition, denoted by SDA & SCL HIGH, followed by SDA LOW, SCL HIGH
         A 7-bit device address, MSB first (0x8/0xC = 1, 0x0/0x4 = 0)
         A R/W bit (0x8/0xC = read, 0x0/0x4 = write)
         An ACK bit (0x8/0xC = NAK, 0x0/0x4 = ACK)
         If the bus direction is WRITE, then
             A register address for read/write
             zero or more additional data bytes
         Else (the bus direction is READ)
            One or more additional data bytes
         Endif

    This version uses a fixed-size (2048 bytes) array instead of tonton81's circular buffer library.
    
    
    To generalize for any I2C slave device rather than just the MPU6050 IMU, comment out the 
    "#define MPU6050_SPECIFIC line below. This will remove all MPU6050 specific code

*/


Additional information can be found on my blog site at

https://www.fpaynter.com/2020/01/teensy-i2c-sniffer-for-mpu6050-part-ii/

and on the PJRC forum at

https://forum.pjrc.com/threads/59160-Teensy-I2C-Sniffer-for-MPU6050?p=227243#post227243