NRF52LL Quadrature decoder

Thanks Robin,

The specification in question is http://infocenter.nordicsemi.com/pdf/nRF52832_PS_v1.1.pdf section 36 starting on page 346, also linked from the low-level library page http://www.espruino.com/NRF52LL
It is actually from there I found out that the chip indeed had hardware support for quadrature decoding. The encoder I use is RLS RM08 https://www.rls.si/en/fileuploader/download/download/?d=1&file=custom%2Fupload%2FRM08D01_12.pdf, but I think it would work just as well with more common optical encoders like HEDL5540 etc.

connecting it to a counter

Has a specific model and make been selected? What is the doc link for that also?

I meant counter in the nRF52, like how it is done for counting button clicks in the example of low level library. Maybe not necessary, I am a bit unused to the low-level specification documentation (linked above).

What access speed is expected? How many pulses must read and over what duration?

We have 1024 counts per revolution and in our case we use it to detect angle of a manual axis rotation so it is perhaps max 10.000 counts per second. My software solution was just intended as a proof of concept but it works if I rotate slowly (~4s per turn), but skips counts if i turn faster.

Here is the js code. Thanks for the inlineC suggestion, I will try and see if I can use it too.

// D25 Green A channel
// D26 Grey  B channel
const stable = [0,-1,1,0,1,0,0,-1,-1,0, 0,1, 0,1, -1, 0];
var encoder_raw = [false, false];
var counter = 0;
var prev_state = -1;

var  on = false;
setInterval(function() {
  on = !on;
  LED1.write(on);
  console.log("Counter " + counter);
}, 100);

const encoder_callback = function(AB, value)
{
    encoder_raw[AB]=value;
    var cur_state = encoder_raw[0] << 1 | encoder_raw[1];
    if(prev_state < 0) prev_state = cur_state;
    counter += stable[prev_state << 2 | cur_state];
    prev_state=cur_state;
};

setWatch(function(e) {encoder_callback(0,true); }, D25, { repeat: true, edge: 'rising' });
setWatch(function(e) {encoder_callback(0,false);}, D25, { repeat: true, edge: 'falling' });
setWatch(function(e) {encoder_callback(1,true); }, D26, { repeat: true, edge: 'rising' });
setWatch(function(e) {encoder_callback(1,false);}, D26, { repeat: true, edge: 'falling' });