failing to read data pin based on clock pin with setWatch and digitalRead

[espruino-discuss2]

Posted at 2018-06-24 by mkol5222

Hello,
I am trying to port Arduino C code to Puck.JS JavaScript
and I think I have potential timing issue with use of setWatch on clock PIN
to read data from data PIN similar to code below.

Is it possible to find optimal solution to interpret my input PINs
even with setWatch callback?
I do not get consistent results reading the data and I am worried that
only solution would be to have native code handling it?

What I try to do - storing each data bit on clock edge to array (to be interpreted later)

var req = 31; //mic REQ

var dat = 1; //mic Data line

var clk = 2; //mic Clock line

var i = 0;
var a=[];

pinMode(clk, 'input_pullup');

pinMode(dat, 'input_pullup');

pinMode(clk, 'input_pullup');

setWatch(function () {
        b = digitalRead(dat);
        if (i < 52) {
          a.push(b);
          i++;
        }


}, clk, {
    edge: "rising",
    debounce: 0,
    repeat: true
});

Arduino code was similar to
Arduino is using loop driven by CLK pin vs. Espruino based on JavaScript callback with set Watch for CLK edge...
My HW is Puck.JS.

void loop()
{ 
    digitalWrite(req, HIGH); // generate set request
    for (i = 0; i < 13; i++)
    {
        k = 0;
        for (j = 0; j < 4; j++)
        {

            while (digitalRead(clk) == LOW) {}
            while (digitalRead(clk) == HIGH) {}
            bitWrite(k, j, (digitalRead(dat) & 0x1)); // read data bits, and reverse order )
        }
        mydata[i] = k;
    }
...

[espruino-discuss2]

Posted at 2018-06-25 by Wilberforce

what hardware are interfacing too? there might already be a module you can use - or something similiar that you could modify.

[gfwilliams]

Posted at 2018-06-25 by @gfwilliams

The issue you're hitting is that setWatch timestamps the events and put them in a queue to execute with JS - but as you notice it's won't execute JavaScript in the interrupt itself.

One way around this is to actually watch the data pin for changes as well:

var currentDat = 0;
setWatch(function (e) { currentDat = e.state; }, dat, {repeat:true});
setWatch(function () {
        if (i < 52) {
          a.push(currentDat);
          i++;
        }...

However reading clocked data is a really common thing to want to do, so in version 1v96 I added the ability to also record a separate data source using setWatch:

setWatch(function (e) {
        if (i < 52) {
          a.push(e.data);
          i++;
        }
}, clk, {
    edge: "rising",
    debounce: 0,
    repeat: true,
   data : dat
});

So that should do exactly what you want.

More info at: http://www.espruino.com/Reference#l__global_setWatch

As @wilberforce says, depending on what you're trying to connect to there might also be a way to set up the underlying hardware to help you out.

[espruino-discuss2]

Posted at 2018-06-25 by mkol5222

@gordon and @wilberforce Many thanks for quick response. Suggestion to use new setWatch functionality for reading data pin exactly resolved timing issues with data readings.

I am amazed how Puck.JS and Espruino JavaScript approach makes prototyping so easy including making easy publishing of data via BLE GATT service. We have submitted order for additional Espruino gatgets to learn even more.

[gfwilliams]

Posted at 2018-06-26 by @gfwilliams

Great, thanks!