File content as of revision 0:c9e647421e54:

#include "mbed.h"
#include "encoder.h"
#include "MODSERIAL.h"

#define K_P 0.015//184997836671646 
#define K_I 0.//000824387821287097
#define K_D 0.077//972091946803081

void coerce(float * in, float min, float max);
float pid(float setpoint, float measurement);

volatile bool looptimerflag;

void setlooptimerflag(void)
{
    looptimerflag = true;
}

int main() {
    Encoder motor1(PTD0,PTC9);
    MODSERIAL pc(USBTX,USBRX);
    PwmOut pwm_motor(PTA12);
    DigitalOut motordir(PTD3);
    AnalogIn   potmeter(PTC2);
    pc.baud(115200);
    Ticker looptimer;
    looptimer.attach(setlooptimerflag,0.01);   
    while(1) {
        static float setpoint = 0;
        float new_pwm;
        while(!looptimerflag);
        looptimerflag = false;
        setpoint = (potmeter.read()-0.5)*2000;
        new_pwm = pid(setpoint, motor1.getPosition());
        coerce(&new_pwm, -1,1);
        if(new_pwm > 0)
            motordir = 1;
        else
            motordir = 0;  
        pwm_motor.write(abs(new_pwm));
    }
}

void coerce(float * in, float min, float max)
{
    *in > min ? *in < max? : *in = max: *in = min;
}


float pid(float setpoint, float measurement)
{
        //static int16_t setpoint = 0            //static int16_t setpoint = 0      
        float error;
        static float prev_error = 0;
        float           out_p = 0;
        static float    out_i = 0;
        float           out_d = 0;
        error  = setpoint-measurement;
        out_p  = error*K_P;
        out_i += error*K_I;
        out_d = (error-prev_error)*K_D;
        coerce(&out_i,-0.5,0.5);
        prev_error = error;
        return out_p + out_i + out_d;    
}