how do I code this?

Timing and Interrupts The STM32 has four built-in timericounters. These counters count based upon a clock input. The clock input is based upon the 72MHz microcontroller clock. The 72MHz is first divided by a "prescaler." The prescaler divides the 72MHz clock by a value between one (1) and 2. For example, if the prescaled value is 1000 , the 72MHz clock is scaled to a 72kHz clock. This scaled clock is input to a 16-bit registerioounter. The 16-bit register/counter counts (at the prescaled rate) from 0 to 65535 . (The registericounter could count from zero to a value less that 65535 if programmed to do so.) When the 16-bit register/counter counts to 65535, an "overflow" condition occurs. So if the prescaled clock is 72kHz, an overflow occurs every 65536/72000=0.91022 seconds. The best way to track the overflows is with an "interrupt service routine." This routine will be executed whenever an overllow occurs. Let us call the interrupt service routine "overflow () " We can get this interrupt service routine to execute by using a "member function" called "attachInterrupt () " The Arduino/STM32 code to have the timer execute "overflow () (upon overfiow) is shown in Listing 1 . Listing 1. Timer code with interrupt service routine. The overtlow () routine gets executed once every 0.91022 seconds