File content as of revision 0:6d4f91decc4f:

#include "FastPWM.h"
#include "mbed.h"
#include "PwmIn.h"
#include "USBSerial.h"

// using fastpwm signal as a clock signal to be used to trigger the counter whilst the signal I want to measure is high. 
// to get this to work properly I believe I will need to use nested interrupts along with setting interupt priorities. This is so that
// when the signal I want to read  (led) causes an interrupt on a rising edge whilst this value is high I want the clock trigger to interrupt a seperate pin 
// which will continuoulsy count until the (led) signal causes another interrupt by going low.

// clkin is currently set as a DigitalIn but this likely needs to become an interrupt.

USBSerial serial;

FastPWM clkoutput(p20);
DigitalIn clkin(p8);
InterruptIn led(p7);
Ticker display;

int count;
int count_2;
int t_rise;
int t_fall;
int t_period = 0;


void clock_pulse() {
    
      clkoutput.period(8e-7); //around 1.2 MHz signal
    clkoutput.write(0.5f);   // 50% duty cycle
    }
    
    
void rise() { // rising edge interrupt routine 
  
   while (led && clkin) {           // whilst the signal I want to measure is high (led) and the clk signal (clkin) is high increment the counter
           //  if (clkin) {
                 count++;
                 }
  //  if (led && clkoutput) {
            
        //    count++;
   //     while (led) {
     //        if (clkin) {
     //            count++;
      //           }
             t_fall = count_2;   
            // count_2 = 0;
             }
  //  }
    
  void fall() { // falling edge interrupt routine
      
      while (!led && clkin) {  // whilst the signal I want to measure is low and the clk signal is high increment counter 2
          count_2++;
          }
          t_rise = count;
         // count = 0;
       
      }
  
// }

/*void period() {
    t_period = count;
    count = 0;
    }  
*/

void disp() {
    
    serial.printf("count is %d \n\r" , t_rise);
    serial.printf("count_2 is %d \n\r" , t_fall);   
    }


int main()
{
    clock_pulse();
    
    led.rise(&rise); // set rising edge interrupt and call rise function
    led.fall(&fall); // set falling edge interrupt and call fall function       
             //count = 0;
           //  }
   
    display.attach(&disp, 2); // ticker function to display results every 2 seconds

   while (1) {
         
      //   while (led) {
          //   if (clkin) {
          //       count++;
            //     }
            // count = 0;
             //}
         
        // if (led == 1) && (clkoutput == 1) {
            
          //  count++;
         
           /*
  
  while (led) {
      
      if (clkin) {
          
          count++;
                   }        
          
  */
         
         
            }

        //serial.printf("Pulsewidth is %.2f \n\r" , pa.pulsewidth());
                




}