include "mbed.h"

DigitalIn qa(p13);      //phase a of the quadrature encoder
DigitalIn qb(p14);      //phase b of the quadrature encoder

Serial pc(USBTX,USBRX);
Ticker qt;              //create a timer to sample the keys
int dir=0;              //hold the signed value corresponding to the number of clicks left or right since last sample
int qslast=0;           //keep a record of the last actioned sample state of the Qb+Qa outputs for comparison on each interrupt

void qdec (void){
    int qas=qa.read();          // read the state of phase a                qa=  __|-----|_____|-----|_____
    int qbs=qb.read();          // read the state of phase b                qb=  -----|_____|-----|_____|-
    int qs=qbs<<1+qas;          // create a two bit value out of qb and qa, qs=  10 11 01 00 10 11 01 00
    switch (qslast) {           // depending on the last actionable state     =   2  3  1  0  2  3  1  0
        case 0:                 // if last state was 0,                            <- left     right->    (direction of know rotation)
            if (qs==1) {        //      and the currently sampled state is 1, then the knob was rotated left, 
                dir--;          //      so subtract one from the diretion accumulator        
                qslast=1;       //      and set the new last state to 1 and  leave the if statement   
                break;
            } else if (qs==2) { //      otherwise if the currently sampled state is 2, then the knob was rotated right,
                dir++;          //      so increase the rotation accumulator
                qslast=2;       //      and set the new last state to 
                break;
            }
        case 1:
            if (qs==3) {        
                dir--;
                qslast=3;
                break;
            } else if (qs==0) {
                dir++;
                qslast=0;
                break;
            }
        case 2:
            if (qs==0) {
                dir--;
                qslast=0;
                break;
            } else if (qs==3) {
                dir++;
                qslast=3;
                break;
            }
        case 3:
            if (qs==2) {
                dir--;
                qslast=2;
                break;
            } else if (qs==1) {
                dir++;
                qslast=1;
                break;
            }
        default:
            break;
    }
}

int getrot() {          // function to read the rotation accumulator, and once read, reset it to zero
    int res=dir;        // this allows the knob to be rotated "while im not looking at it' and still return the 
    dir=0;              // actual number of clicks that have been rotated since last time I was checking it.
    return (res);
}

int main() {
    int counter=0;

    qa.mode(PullUp);                                    // qa is set with a built in pull-up resistor
    qb.mode(PullUp);                                    // qb is set with a built in pull-up resistor    
    qt.attach_us(&qdec,5000);                           // make the quadrature decoder function check the knob once every 1000us = 1ms
    while (1)                                           // loop forever
    {
        printf("dir = %d,%d\r\n",dir,qslast);           // print the value of the rotation accumulator register
        wait_ms(200);                                   // every 200 ms.
    }
}