ardupilot/libraries/AP_RSSI/AP_RSSI.cpp

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <AP_RSSI/AP_RSSI.h>
#include <utility> 

extern const AP_HAL::HAL& hal;


const AP_Param::GroupInfo AP_RSSI::var_info[] = {

    // @Param: TYPE
    // @DisplayName: RSSI Type
    // @Description: Radio Receiver RSSI type. If your radio receiver supports RSSI of some kind, set it here, then set its associated RSSI_XXXXX parameters, if any.
    // @Values: 0:Disabled,1:AnalogPin,2:RCChannelPwmValue
    // @User: Standard
    AP_GROUPINFO("TYPE", 0, AP_RSSI, rssi_type,  0),

    // @Param: ANA_PIN
    // @DisplayName: Receiver RSSI analog sensing pin
    // @Description: This selects an analog pin where the receiver RSSI voltage will be read.
    // @Values: 0:APM2 A0, 1:APM2 A1, 13:APM2 A13, 103:Pixhawk SBUS
    // @User: Standard
    AP_GROUPINFO("ANA_PIN", 1, AP_RSSI, rssi_analog_pin,  0),

    // @Param: PIN_LOW
    // @DisplayName: Receiver RSSI voltage low
    // @Description: This is the voltage value that the radio receiver will put on the RSSI_ANA_PIN when the signal strength is the weakest. Since some radio receivers put out inverted values from what you might otherwise expect, this isn't necessarily a lower value than RSSI_PIN_HIGH. 
    // @Units: Volt
    // @Increment: 0.01
    // @Range: 0 5.0
    // @User: Standard
    AP_GROUPINFO("PIN_LOW", 2, AP_RSSI, rssi_analog_pin_range_low, 0.0f),

    // @Param: PIN_HIGH
    // @DisplayName: Receiver RSSI voltage high
    // @Description: This is the voltage value that the radio receiver will put on the RSSI_ANA_PIN when the signal strength is the strongest. Since some radio receivers put out inverted values from what you might otherwise expect, this isn't necessarily a higher value than RSSI_PIN_LOW. 
    // @Units: Volt
    // @Increment: 0.01
    // @Range: 0 5.0
    // @User: Standard
    AP_GROUPINFO("PIN_HIGH", 3, AP_RSSI, rssi_analog_pin_range_high, 5.0f),

    // @Param: CHANNEL
    // @DisplayName: Receiver RSSI channel number
    // @Description: The channel number where RSSI will be output by the radio receiver.
    // @Units: 
    // @Values: 5:Channel5,6:Channel6,7:Channel7,8:Channel8
    // @User: Standard
    AP_GROUPINFO("CHANNEL", 4, AP_RSSI, rssi_channel,  0),

    // @Param: CHAN_LOW
    // @DisplayName: Receiver RSSI PWM low value
    // @Description: This is the PWM value that the radio receiver will put on the RSSI_CHANNEL when the signal strength is the weakest. Since some radio receivers put out inverted values from what you might otherwise expect, this isn't necessarily a lower value than RSSI_CHAN_HIGH. 
    // @Units: Microseconds
    // @Range: 0 2000
    // @User: Standard
    AP_GROUPINFO("CHAN_LOW", 5, AP_RSSI, rssi_channel_low_pwm_value,  1000),

    // @Param: CHAN_HIGH
    // @DisplayName: Receiver RSSI PWM high value
    // @Description: This is the PWM value that the radio receiver will put on the RSSI_CHANNEL when the signal strength is the strongest. Since some radio receivers put out inverted values from what you might otherwise expect, this isn't necessarily a higher value than RSSI_CHAN_LOW. 
    // @Units: Microseconds
    // @Range: 0 2000
    // @User: Standard
    AP_GROUPINFO("CHAN_HIGH", 6, AP_RSSI, rssi_channel_high_pwm_value,  2000),

    AP_GROUPEND
};

// Public
// ------

// constructor
AP_RSSI::AP_RSSI()
{       
    AP_Param::setup_object_defaults(this, var_info);
}

// destructor
AP_RSSI::~AP_RSSI(void)
{       
}

// Initialize the rssi object and prepare it for use
void AP_RSSI::init()
{
    // a pin for reading the receiver RSSI voltage. The scaling by 0.25 
    // is to take the 0 to 1024 range down to an 8 bit range for MAVLink    
    rssi_analog_source = hal.analogin->channel(ANALOG_INPUT_NONE);    
}

// Read the receiver RSSI value as a float 0.0f - 1.0f.
// 0.0 represents weakest signal, 1.0 represents maximum signal.
float AP_RSSI::read_receiver_rssi()
{
    // Default to 0 RSSI
    float receiver_rssi = 0.0f;  

    switch (rssi_type) {
        case RssiType::RSSI_DISABLED :
            receiver_rssi = 0.0f;
            break;
        case RssiType::RSSI_ANALOG_PIN :
            receiver_rssi = read_pin_rssi();
            break;
        case RssiType::RSSI_RC_CHANNEL_VALUE :
            receiver_rssi = read_channel_rssi();
            break;
        default :   
            receiver_rssi = 0.0f;
            break;
    }    
                  
    return receiver_rssi;
}

// Read the receiver RSSI value as an 8-bit integer
// 0 represents weakest signal, 255 represents maximum signal.
uint8_t AP_RSSI::read_receiver_rssi_uint8()
{
    return read_receiver_rssi() * 255; 
}

// Private
// -------

// read the RSSI value from an analog pin - returns float in range 0.0 to 1.0
float AP_RSSI::read_pin_rssi()
{
    rssi_analog_source->set_pin(rssi_analog_pin);
    float current_analog_voltage = rssi_analog_source->voltage_average();

    return scale_and_constrain_float_rssi(current_analog_voltage, rssi_analog_pin_range_low, rssi_analog_pin_range_high);
}

// read the RSSI value from a PWM value on a RC channel
float AP_RSSI::read_channel_rssi()
{
    uint16_t rssi_channel_value = hal.rcin->read(rssi_channel-1);
    float channel_rssi = scale_and_constrain_float_rssi(rssi_channel_value, rssi_channel_low_pwm_value, rssi_channel_high_pwm_value);
    return channel_rssi;    
}

// Scale and constrain a float rssi value to 0.0 to 1.0 range 
float AP_RSSI::scale_and_constrain_float_rssi(float current_rssi_value, float low_rssi_range, float high_rssi_range)
{    
    float rssi_value_range = fabsf(high_rssi_range - low_rssi_range);
    if (is_zero(rssi_value_range)) {
        // User range isn't meaningful, return 0 for RSSI (and avoid divide by zero)
        return 0.0f;   
    }
    // Note that user-supplied ranges may be inverted and we accommodate that here. 
    // (Some radio receivers put out inverted ranges for RSSI-type values).    
    bool range_is_inverted = (high_rssi_range < low_rssi_range);
    // Constrain to the possible range - values outside are clipped to ends 
    current_rssi_value = constrain_float(current_rssi_value, 
                                        range_is_inverted ? high_rssi_range : low_rssi_range, 
                                        range_is_inverted ? low_rssi_range : high_rssi_range);    

    if (range_is_inverted)
    {
        // Swap values so we can treat them as low->high uniformly in the code that follows
        current_rssi_value = high_rssi_range + abs(current_rssi_value - low_rssi_range);
        std::swap(low_rssi_range, high_rssi_range);        
    }

    // Scale the value down to a 0.0 - 1.0 range
    float rssi_value_scaled = (current_rssi_value - low_rssi_range) / rssi_value_range;
    // Make absolutely sure the value is clipped to the 0.0 - 1.0 range. This should handle things if the
    // value retrieved falls outside the user-supplied range.
    return constrain_float(rssi_value_scaled, 0.0f, 1.0f);
}