The foliowing code should switch a buzzer on and off at a frequency of $4Hz.$ Complete the missing parts?

byte $*$ptr$\_$PORTD:

byte $*$ptr$\_$DDRD:

unsigned long $Tp=0$;

unsigned Iong Tc:

void setup$()$

ptr$\_$PORTD$=0$x$2$B

ptr$\_$DDRD$=0$x$2$A

$*$ptr$\_$DDRD$=*$ptr$\_$DDRD $|$ B$00010000$;

$\}$void loop $()\{$