File content as of revision 0:ed48c1d4c02f:

//NuMaker-PFM-NUC472 PWM0 output Siren to a speaker
#include "mbed.h"

#define Ambulance_Siren_Low   650
#define Ambulance_Siren_High  900
#define Ambulance_Siren_L_period 400 // 0.4 sec
#define Ambulance_Siren_H_period 600 // 0.6 sec

#define PoliceCar_Siren_Low   650
#define PoliceCar_Siren_High 1450
#define PoliceCar_Siren_L_duration 230 // 0.23 sec
#define PoliceCar_Siren_H_duration 100 // 0.1  sec

PwmOut pwm0(PF_9); // PWM0 pin 

void Ambulance_Siren(uint32_t siren_no)
{
    int i;
    for (i=0; i<siren_no; i++) {
        pwm0.period_us(1000000/Ambulance_Siren_Low);
        pwm0.pulsewidth_us(1000000/Ambulance_Siren_Low/2); // set duty cycle to 50%        
        Thread::wait(Ambulance_Siren_L_period);
        pwm0.period_us(1000000/Ambulance_Siren_High);
        pwm0.pulsewidth_us(1000000/Ambulance_Siren_High/2); // set duty cycle to 50% 
        Thread::wait(Ambulance_Siren_H_period);
    }
    pwm0.pulsewidth_us(0);
}

void PoliceCar_Siren(uint32_t siren_no)
{
    int i, j;
    int siren_freq;
    
    for (i=0; i<siren_no; i++) {
        siren_freq = PoliceCar_Siren_Low;
        for (j=0; j<(PoliceCar_Siren_L_duration); j++) {
            pwm0.period_us(1000000/siren_freq);
            pwm0.pulsewidth_us(1000000/siren_freq/2); // set duty cycle to 50%
            Thread::wait(1);
            siren_freq = siren_freq + (PoliceCar_Siren_High - PoliceCar_Siren_Low)/230; 
        }       
        siren_freq = PoliceCar_Siren_High;
        for (j=0; j<PoliceCar_Siren_L_duration; j++) {
            pwm0.period_us(1000000/siren_freq);
            pwm0.pulsewidth_us(1000000/siren_freq/2); // set duty cycle to 50%
            Thread::wait(1);
            siren_freq = siren_freq - (PoliceCar_Siren_High - PoliceCar_Siren_Low)/100; 
        }           
    }
    pwm0.pulsewidth_us(0);
}

int main()
{
      while(1) {
        Ambulance_Siren(5);   
        PoliceCar_Siren(5);
        }
}