.. highlight:: javascript

Barometer
=========
A barometer is a scientific instrument that is used to measure air pressure in a certain environment. The absolute barometric pressure sensor can measure pressure from 300 Pascal to 1100 hPa.

MetaWear RPro and Cpro, MMR, MMC, MTR, and MetaEnvironment boards come with a Bosch barometer.  

The specific barometer model varies between the boards although both barometers are nearly identical save for a few settings.  Bosch barometer functions are defined in the 
`barometer_bosch.h <https://mbientlab.com/docs/metawear/cpp/latest/barometer__bosch_8h.html>`_ header file where functions containing ``baro_bosch`` 
are barometer agnostic where as functions with ``baro_bmp280`` and ``baro_bme280`` are for those specific barometers. 

Users can programatically determine which barometer is on their board with the 
`mbl_mw_metawearboard_lookup_module <https://mbientlab.com/docs/metawear/cpp/latest/metawearboard_8h.html#ad9c7e7f60f77fc1e929ac48c6a3ffb9b>`_ function. ::

    let gyroType = MetaWear.mbl_mw_metawearboard_lookup_module(device.board, MBL_MW_MODULE_BAROMETER);
    switch (gyroType) {
        case MBL_MW_MODULE_BARO_TYPE_BMP280:
            console.log("BMP280 barometer")
            break;
        case MBL_MW_MODULE_BARO_TYPE_BME280:
            console.log("BME280 barometer")
            break;
        case UInt8(MBL_MW_MODULE_TYPE_NA):
            console.log("no barometer")
            break;
        default:
            console.log("unknown barometer")
            break;
    }

Sensor Configuration
--------------------
The Bosch barometers have 3 configurable parameters: 

* Oversampling
* Infinite impulse filter (iir) coefficient
* Standby time

These operational parameters work in conjunction to control the noise, output resolution, and sampling rate.  When you are done setting the configuration, 
call `mbl_mw_baro_bosch_write_config <https://mbientlab.com/docs/metawear/cpp/latest/barometer__bosch_8h.html#ac763f27505e504d7c7ebd37c7bc98aa6>`_ to 
write the changes to the sensor. ::

    // Set oversampling to ultra high resolution
    MetaWear.mbl_mw_baro_bosch_set_oversampling(device.board, MBL_MW_BARO_BOSCH_OVERSAMPLE_ULTRA_HIGH);
    
    // Set standby time to 62.5ms or closest valid value
    MetaWear.mbl_mw_baro_bosch_set_standby_time(device.board, 62.5);
    
    // Set iir filter coefficient
    MetaWear.mbl_mw_baro_bosch_set_iir_filter(device.board, MBL_MW_BARO_BOSCH_IIR_FILTER_AVG_4);
    
    // Write configuration to the sensor
    MetaWear.mbl_mw_baro_bosch_write_config(device.board);

Pressure Sampling
-----------------
Pressure data is represented as a float and is in units of Pascals.   To receive pressure data, simply subscribe or log the pressure data signal and 
then start the sensor. ::

    console.log('Get barometer.')
    let baro = MetaWear.mbl_mw_baro_bosch_get_pressure_data_signal(device.board);

    console.log('Set up stream.')
    MetaWear.mbl_mw_datasignal_subscribe(baro, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer((ctx, pointer) => {
        var data = pointer.deref();
        var value = data.parseValue();
        console.log('epoch: ' + data.epoch + ' pressure: ' + value);
    }))

    console.log('Start barometer.');
    MetaWear.mbl_mw_baro_bosch_start(device.board);

Altitude Sampling
-----------------
Altitude data is represented as a float and is in units of meters.  To receive altitude data, simply subscribe or log the altitude data signal and then 
start the sensor. :: 

    console.log('Setup barometer.')
    MetaWear.mbl_mw_baro_bosch_set_oversampling(device.board, MBL_MW_BARO_BOSCH_OVERSAMPLING_ULTRA_LOW_POWER);
    MetaWear.mbl_mw_baro_bosch_set_iir_filter(device.board, MBL_MW_BARO_BOSCH_IIR_FILTER_OFF);
    MetaWear.mbl_mw_baro_bmp280_set_standby_time(device.board, MBL_MW_BARO_BMP280_STANDBY_TIME_0_5ms);
    MetaWear.mbl_mw_baro_bosch_write_config(device.board);
        
    console.log('Get barometer.')
    let baro = MetaWear.mbl_mw_baro_bosch_get_altitude_data_signal(device.board);

    console.log('Set up stream.')
    MetaWear.mbl_mw_datasignal_subscribe(baro, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer((ctx, pointer) => {
        var data = pointer.deref();
        var value = data.parseValue();
        console.log('epoch: ' + data.epoch + ' pressure: ' + value);
    }))

    console.log('Start barometer.');
    MetaWear.mbl_mw_baro_bosch_start(device.board);