ardupilot/libraries/AP_RangeFinder/AP_RangeFinder_Lanbao.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/>.
 */
/*
  driver for Lanbao PSK-CM8JL65-CC5 Lidar
 */
#include "AP_RangeFinder_Lanbao.h"

#if AP_RANGEFINDER_LANBAO_ENABLED

#include <AP_HAL/AP_HAL.h>
#include <AP_Math/crc.h>
#include <stdio.h>

extern const AP_HAL::HAL& hal;

/*
  this sensor has no way of reporting "out of range", it will keep
  reporting distances at of around 7 to 8 meters even when pointed at
  the sky. For this reason we limit the max range to 6 meters as
  otherwise we may be giving false data
 */
#define LANBAO_MAX_RANGE_M 6

// read - return last value measured by sensor
bool AP_RangeFinder_Lanbao::get_reading(float &reading_m)
{
    if (uart == nullptr) {
        return false;
    }

    float sum_range = 0;
    uint32_t count = 0;

    // format is: [ 0xA5 | 0x5A | distance-MSB-mm | distance-LSB-mm | crc16 ]

    // read any available lines from the lidar
    int16_t nbytes = uart->available();
    while (nbytes-- > 0) {
        int16_t b = uart->read();
        if (b == -1) {
            break;
        }
        if (buf_len == 0 && b != 0xA5) {
            // discard
            continue;
        }
        if (buf_len == 1 && b != 0x5A) {
            // discard
            if (b == 0xA5) {
                buf[0] = b;
            } else {
                buf_len = 0;
            }
            continue;
        }
        buf[buf_len++] = b;
        if (buf_len == sizeof(buf)) {
            buf_len = 0;
            uint16_t crc = (buf[5]<<8) | buf[4];
            if (crc != calc_crc_modbus(buf, 4)) {
                // bad CRC, discard
                continue;
            }
            sum_range += float((buf[2]<<8) | buf[3]) * 0.001;
            count++;
        }
    }
    if (count > 0) {
        reading_m = (sum_range / count);
        return reading_m <= LANBAO_MAX_RANGE_M?true:false;
    }
    return false;
}

#endif  // AP_RANGEFINDER_LANBAO_ENABLED