APLL lock indication functionality can be checked by using CPU Timer and the user defined software. Timer can be configured for a fixed number of cycles before which APLL is expected to get locked. Case where APLL does not get locked before the Timer expires (that is, taking more cycles than expected), timer interrupt is triggered to CPU and further action can be taken by the user-defined software. In order to ensure the correctness of APLL clock and hence the system clock generation, it is recommended to use the standard clock sources for timer module (like INTOSC, Crystal and so forth) instead of system clock for checking the APLL clock generation correctness.