# Does SysTick_Handler() have to be in main file?

Does the CMSIS SysTick_Handler() have to be placed in the main file (i.e. same file where it is configured)?

If not, how would I go about placing it elsewhere? Is it just a matter of defining the function in another .cpp file, and including "LPC17xx.h"?

You don't need any header included, just extern "C" void SysTick_Handler(){ ... } in an implementation file.
• @19172281 Not easily, no. A member function has an inherent this pointer passed to it as the first argument, which can't happen if it's called from elsewhere. The easiest thing to do is have your SysTick_Handler call a function on an instance of your class. – Colin Apr 3 '19 at 18:57