DC Motor cascade PID control (stable 90 degree)

Maxon DCX35L Motor cascade PID control with AVR 8535
1. Target degree(Input) goes into position controller and then target angular velocity(output) comes out.
2. Target angular velocity(Input) goes into speed controller and then target current(output) comes out.
3. Target current goes into current controller and then target voltage(output) comes out.
4. target voltage (-12V ~ 12V) is transformed to PWM value( -255~255) and moves the motor.
Each controller's output has saturation(cuz if error gets larger, it will blow up the board).
AVR