I2C.getBitrate() would be nice

[espruino-discuss3]

Posted at 2016-01-17 by luwar

Currently I'm developing an Espruino module for an I2C sensor which is not able to run with the default bitrate of 400 kHz.

I want to ensure that nobody fall into the same trap to forget the bitrate parameter in I2C.setup(). I know: "Read the datasheet carefully ...". But better would be an automatic check with a human readable hint about the wrong usage.

Is it possible to get the bitrate of an I2C instance to check the correct usage in the connect()-methods or directly in the constructor function of i2c-sensors, e.g.

    exports.connect = function ( /*=I2C*/i2c ) {
      var br = i2c.getBitrate();
      if (br && (br < 10000 || br > 100000)) {
        throw new Error( "The maximum clock frequency is 100 kHz and the minimum is 10 kHz." );
      }
      return new MLX90614( i2c );
    };

[espruino-discuss3]

Posted at 2016-01-18 by @gfwilliams

The default bitrate is actually 50000 (at least on proper Espruino boards)... Which one are you using?

You can check i2c._options.bitrate - however if the use didn't initialise I2C or didn't specify a bitrate then it won't be there, so you'd have to do something like:

var br = (i2c._options && i2c._options.bitrate) || 50000;
if (br < 10000 || br > 100000) { ....

This could be built into Espruino itself as a function - but then you'd have to wait for the next version before your code would work.

---

Posted at 2016-01-18 by luwar

The default bitrate is actually 50000 (at least on proper Espruino boards)... Which one are you using?

Good to know. I thought the default bitrate were higher. I'm using a classic and different pico boards. So it is unnecessary in my case to check the bitrate if nobody increase it explicitly. Ok, thanks.
i2c._options.bitrate looks more like an internal API. I would prefer a documented getBitrate() method but that's only my viewpoint.

---

Posted at 2016-01-19 by @gfwilliams

There is an issue open for this (not specifically on I2C): espruino/Espruino#119

I've just linked this forum post. I'll have a think about a nice way of doing it - the thing really is finding a way of doing it that uses up very little memory. Some of the boards without much flash have a lot of trouble getting Espruino in at the moment (literally ~300 bytes free or so) - normally I'd just not include non-vital functions on those boards - but with something like this, modules that used the function would just refuse to work of the function didn't exist.