>be me, embedded developer
>wake up
>write a function that configures the serial port
>write an RX interrupt that just prints "hello" to test
>doesnt work
>check scope
>"hmm, maybe the baudrate is wrong"
>correct baudrate
>doesnt work
>measure the baudrate
>correct it again
>doesnt work
>set breakpoint in interrupt
>doesnt trigger
>make clean; make; make upload
>doesnt work
>think for a while
>you never called the new function from main
>call it
>works