.. highlight:: swift

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 = mbl_mw_metawearboard_lookup_module(board, MBL_MW_MODULE_BAROMETER)
    switch UInt8(gyroType) {
        case MBL_MW_MODULE_BARO_TYPE_BMP280:
            print("BMP280 barometer")
            break
        case MBL_MW_MODULE_BARO_TYPE_BME280:
            print("BME280 barometer")
            break
        case UInt8(MBL_MW_MODULE_TYPE_NA):
            print("no barometer")
            break
        default:
            print("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
    mbl_mw_baro_bosch_set_oversampling(board, MBL_MW_BARO_BOSCH_OVERSAMPLE_ULTRA_HIGH)
    
    // Set standby time to 62.5ms or closest valid value
    mbl_mw_baro_bosch_set_standby_time(board, 62.5f)
    
    // Set iir filter coefficient
    mbl_mw_baro_bosch_set_iir_filter(board, MBL_MW_BARO_BOSCH_IIR_FILTER_AVG_4)
    
    // Write configuration to the sensor
    mbl_mw_baro_bosch_write_config(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. ::

    #include "metawear/core/datasignal.h"
    
    void setup_pressure_stream(MblMwMetaWearBoard* board) {
        auto data_handler = [](const MblMwData* data) -> void {
            // Cast value to float*
            printf("%.3fPa\n", *((float*) data->value));
        };
        auto pa_signal= mbl_mw_baro_bosch_get_pressure_data_signal(board);
    
        mbl_mw_datasignal_subscribe(pa_signal, data_handler);
        mbl_mw_baro_bosch_start(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. :: 

    mbl_mw_baro_bosch_set_oversampling(device.board, MBL_MW_BARO_BOSCH_OVERSAMPLING_ULTRA_LOW_POWER)
    mbl_mw_baro_bosch_set_iir_filter(device.board, MBL_MW_BARO_BOSCH_IIR_FILTER_OFF)
    mbl_mw_baro_bmp280_set_standby_time(device.board, MBL_MW_BARO_BMP280_STANDBY_TIME_0_5ms)
    mbl_mw_baro_bosch_write_config(device.board)
        
    let signal = mbl_mw_baro_bosch_get_altitude_data_signal(device.board)!
    mbl_mw_datasignal_subscribe(signal, bridge(obj: self)) { (context, obj) in
        let altitude: Float = obj!.pointee.valueAs()
        print(String(format: "%.3f", altitude))
    }
    mbl_mw_baro_bosch_start(device.board)
        
    streamingCleanup[signal] = { // Callback from user
        mbl_mw_baro_bosch_stop(self.device.board)
        mbl_mw_datasignal_unsubscribe(signal)
    }