Main thing that doesn't allow me to implement two 6 DOF units (GY-521 MPU-6050 Module 3 Axis gyro + 3 Axis Accelerometer) into running code is unstable data transfer over I2C connection. When i connect modules to I2C bus for about 30s everything works and after that it stops. I don't have access to an oscilloscope, but as far as I could investigate it seems that error occurs on I2C clock line. This error never happens when there is only PWM chip on bus and no MPU-6050.

My guess is that wires of I2C bus have to high capacity when connected to all 4 chips (STM, PWM, 2x MPU-6050). I2C is limited only by a maximum bus capacitance of 400 pF.

In future I will try to put all 3 peripheral chips on separate I2C busses. I hope that will solve the problem.