ardupilot/libraries/AP_RangeFinder/AP_RangeFinder_LightWareSerial.cpp

/*
   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_HAL/AP_HAL.h>
#include "AP_RangeFinder_LightWareSerial.h"
#include <AP_SerialManager/AP_SerialManager.h>
#include <ctype.h>

extern const AP_HAL::HAL& hal;

#define LIGHTWARE_DIST_MAX_CM           10000
#define LIGHTWARE_OUT_OF_RANGE_ADD_CM   100

/* 
   The constructor also initialises the rangefinder. Note that this
   constructor is not called until detect() returns true, so we
   already know that we should setup the rangefinder
*/
AP_RangeFinder_LightWareSerial::AP_RangeFinder_LightWareSerial(RangeFinder::RangeFinder_State &_state,
                                                               AP_RangeFinder_Params &_params,
                                                               uint8_t serial_instance) :
    AP_RangeFinder_Backend(_state, _params)
{
    const AP_SerialManager &serial_manager = AP::serialmanager();
    uart = serial_manager.find_serial(AP_SerialManager::SerialProtocol_Rangefinder, serial_instance);
    if (uart != nullptr) {
        uart->begin(serial_manager.find_baudrate(AP_SerialManager::SerialProtocol_Rangefinder, serial_instance));
    }
}

/* 
   detect if a Lightware rangefinder is connected. We'll detect by
   trying to take a reading on Serial. If we get a result the sensor is
   there.
*/
bool AP_RangeFinder_LightWareSerial::detect(uint8_t serial_instance)
{
    return AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_Rangefinder, serial_instance) != nullptr;
}

// read - return last value measured by sensor
bool AP_RangeFinder_LightWareSerial::get_reading(uint16_t &reading_cm)
{
    if (uart == nullptr) {
        return false;
    }

    float sum = 0;              // sum of all readings taken
    uint16_t valid_count = 0;   // number of valid readings
    uint16_t invalid_count = 0; // number of invalid readings

    // read any available lines from the lidar
    int16_t nbytes = uart->available();
    while (nbytes-- > 0) {
        char c = uart->read();
        if (c == '\r') {
            linebuf[linebuf_len] = 0;
            const float dist = (float)atof(linebuf);
            if (!is_negative(dist)) {
                sum += dist;
                valid_count++;
            } else {
                invalid_count++;
            }
            linebuf_len = 0;
        } else if (isdigit(c) || c == '.' || c == '-') {
            linebuf[linebuf_len++] = c;
            if (linebuf_len == sizeof(linebuf)) {
                // too long, discard the line
                linebuf_len = 0;
            }
        }
    }

    uint32_t now = AP_HAL::millis();
    if (last_init_ms == 0 ||
        (now - last_init_ms > 1000 &&
         now - state.last_reading_ms > 1000)) {
        // send enough serial transitions to trigger LW20 into serial
        // mode. It starts in dual I2C/serial mode, and wants to see
        // enough transitions to switch into serial mode.
        uart->write("www\r\n");
        last_init_ms = now;
    } else {
        uart->write('d');
    }

    // return average of all valid readings
    if (valid_count > 0) {
        reading_cm = 100 * sum / valid_count;
        return true;
    }

    // all readings were invalid so return out-of-range-high value
    if (invalid_count > 0) {
        reading_cm = MIN(MAX(LIGHTWARE_DIST_MAX_CM, max_distance_cm() + LIGHTWARE_OUT_OF_RANGE_ADD_CM), UINT16_MAX);
        return true;
    }

    // no readings so return false
    return false;
}

/* 
   update the state of the sensor
*/
void AP_RangeFinder_LightWareSerial::update(void)
{
    if (get_reading(state.distance_cm)) {
        // update range_valid state based on distance measured
        state.last_reading_ms = AP_HAL::millis();
        update_status();
    } else if (AP_HAL::millis() - state.last_reading_ms > 200) {
        set_status(RangeFinder::RangeFinder_NoData);
    }
}