ardupilot/libraries/AP_Baro/AP_Baro_HIL.cpp

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-

#include <AP_Baro.h>
#include "AP_Baro_HIL.h"
#include <AP_HAL.h>

extern const AP_HAL::HAL& hal;

// Public Methods //////////////////////////////////////////////////////////////
bool AP_Baro_HIL::init()
{
    _flags.healthy = false;
    return true;
}

// Read the sensor. This is a state machine
// We read one time Temperature (state = 1) and then 4 times Pressure (states 2-5)
uint8_t AP_Baro_HIL::read()
{
    uint8_t result = 0;

    if (_count != 0) {
        hal.scheduler->suspend_timer_procs();
        result = 1;
        Press = _pressure_sum / _count;
        Temp = _temperature_sum / _count;
        _pressure_samples = _count;
        _count = 0;
        _pressure_sum = 0;
        _temperature_sum = 0;
        hal.scheduler->resume_timer_procs();
    }

    return result;
}

void AP_Baro_HIL::setHIL(float pressure, float temperature)
{
    if (pressure > 0) {
        _count = 1;
        _pressure_sum = pressure;
        _temperature_sum = temperature;
        _last_update = hal.scheduler->millis();
        _flags.healthy = true;
    }
}


// ==========================================================================
// based on tables.cpp from http://www.pdas.com/atmosdownload.html

/* 
 Compute the temperature, density, and pressure in the standard atmosphere
 Correct to 20 km.  Only approximate thereafter.
*/
static void SimpleAtmosphere(
	const float alt,                           // geometric altitude, km.
	float& sigma,                   // density/sea-level standard density
	float& delta,                 // pressure/sea-level standard pressure
	float& theta)           // temperature/sea-level standard temperature
{
  const float REARTH = 6369.0f;        // radius of the Earth (km)
  const float GMR    = 34.163195f;     // gas constant
  float h=alt*REARTH/(alt+REARTH);     // geometric to geopotential altitude

  if (h<11.0f)
    {                                                          // Troposphere
      theta=(288.15f-6.5f*h)/288.15f;
      delta=powf(theta, GMR/6.5f);
    }
  else
    {                                                         // Stratosphere
      theta=216.65f/288.15f;
      delta=0.2233611f*expf(-GMR*(h-11.0f)/216.65f);
    }

  sigma=delta/theta;
}


void AP_Baro_HIL::setHIL(float altitude_msl)
{
    float sigma, delta, theta;
    const float p0 = 101325;

    SimpleAtmosphere(altitude_msl*0.001f, sigma, delta, theta);
    float p = p0 * delta;
    float T = 303.16f * theta - 273.16f; // Assume 30 degrees at sea level - converted to degrees Kelvin

    setHIL(p, T);
}

float AP_Baro_HIL::get_pressure() {
    return Press;
}

float AP_Baro_HIL::get_temperature() const {
    return Temp;
}