This is the standard C library clock function from time.h.
clock_t clock( void );
The default implementation of this function uses semihosting.
If the units of clock_t differ from the default of centiseconds, you must define __CLK_TCK on the compiler command line or in your own header file. The value in the definition is used for CLK_TCK and CLOCKS_PER_SEC. The default value is 100 for centiseconds.
If you re-implement clock() you must also re-implement _clock_init().
The returned value is an unsigned integer.