File content as of revision 2:e4f92118a829:

#include "mbed.h"
#include "QEI.h"
#include "math.h"

DigitalOut DirectionPin1(D4);
DigitalOut DirectionPin2(D7);
PwmOut PwmPin1(D5);
PwmOut PwmPin2(D6);
AnalogIn potmeter1(A0);
AnalogIn potmeter2(A1);
Ticker TickerReadPots;

volatile float Duty1;
volatile float Duty2;
volatile float MotorSignal1;
volatile float MotorSignal2;

void ReadPots(void)
{
    Duty1 = potmeter1.read(); // read value potentiometer 1 
    Duty2 = potmeter2.read(); // read value potentiometer 2
 
    MotorSignal1 = 2*Duty1 - 1; //scaling potmeter to motor control signal [0 - 1] --> [(-1) - 1]
    MotorSignal2 = 1 - 2*Duty2;
}

int main()
{
    PwmPin1.period_us(60); // 16.66667 kHz (default period is too slow!)

    TickerReadPots.attach(&ReadPots,0.05); // every 50 milli seconds.
    
    while (true) 
    {
    // motor 1
    DirectionPin1 = MotorSignal1 > 0.0f; //either true or false, CW or CCW
    PwmPin1 = fabs(MotorSignal1); //pwm duty cycle can only be positive, floating point absolute value
    
    // motor 2
    DirectionPin2 = MotorSignal2 > 0.0f; 
    PwmPin2 = fabs(MotorSignal2); 
    
    wait(0.01);  //Do while loop a hundred times per second.
    }
}