How do I continue to receive timed interrupts in an embedded C while loop?

I have a need for an embedded device to stay in a function for one half a second to allow another device to catch up. I used the 1 millisecond timer(r_cg_cmt.c for Renesas IAR IDE) and had a static volatile int delay_time to increment once every 1 millisecond timed interrupt.
using the code:

//counter.c

 //on 1 mS timed interrupt
 gen_purpose_1ms_couter();

 void gen_purpose_1ms_couter_reset( void ){ 
   gen_c->count = 0;
  }


void gen_purpose_1ms_couter( void ){ 
  gen_c->count++;
 } 


//source_file.h

struct gen_counter {
  unsigned int count;
};

extern struct gen_counter *gen_c;

//source_file.c
#include "counter.h"

struct gen_counter *gen_c;

 gen_purpose_1ms_couter_reset();
 while(1){
   if(gen_c->count > 500){
      break;
   }
 }

However this cause the processor (RX231) to stay in the while loop and NOT execute any timed interrupts. Can anyone explain how I can stay in a function for a give amount of time?