Hou to request data to Arduino from Pixhawk via Mavlink?

Question

I connected arduino (serial1) to pixhawk S(serial2).

Could someone explaid me why I have a heartbeat, I can write an rewrite the RC. But I can’t request data from my pixhawk. My pixhawk sys is Vehicle 1,Comp 1 enter image description here

#include "mavlink.h"

// Mavlink variables
int sysid = 1;                   ///< ID 20 for this airplane. 1 PX, 255 ground station
int compid = 158;                ///< The component sending the message
uint8_t target_system = 1;
uint8_t target_component = 1;
int type = MAV_TYPE_GROUND_ROVER;   ///< This system is an airplane / fixed wing
uint8_t autopilot_type = MAV_AUTOPILOT_PIXHAWK;
uint8_t system_mode = MAV_MODE_PREFLIGHT; ///< Booting up
uint32_t custom_mode = 0;                 ///< Custom mode, can be defined by user/adopter
uint8_t system_state = MAV_STATE_STANDBY; ///< System ready for flight
unsigned long request_timer = millis();
unsigned long heartbeat_timer = millis();

void setup() {
  // MAVLink interface start
  Serial1.begin(57600);
  Serial.begin(115200);
}

void loop() {
  doSendHeartbeat();
  dorequest();
  comm_receive() ;
  rc_override(1200, 1200);
}

void doSendHeartbeat() {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];

  if (heartbeat_timer < millis()) {
    mavlink_msg_heartbeat_pack(sysid, compid, &msg, type, autopilot_type, system_mode, custom_mode, system_state);
    uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
    Serial1.write(buf, len);
    heartbeat_timer = millis() + 100;
  }
}
void dorequest() {
  if (request_timer < millis()) {
    Mav_Request_Data();
    request_timer = millis() + 5000;
  }
}

void Mav_Request_Data()
{
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];
  mavlink_msg_request_data_stream_pack(target_system, target_component, &msg, sysid, compid, MAV_DATA_STREAM_ALL, 0x01, 1);
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  Serial1.write(buf, len);
}


void comm_receive() {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];

  mavlink_status_t status;
  while (Serial1.available() > 0) {

    uint8_t c = Serial1.read();
    // Try to get a new message
    if (mavlink_parse_char(MAVLINK_COMM_0, c, &msg, &status)) {
      // Handle message
      Serial.println(msg.msgid);
      switch (msg.msgid) {
        case MAVLINK_MSG_ID_HEARTBEAT:  // #0: Heartbeat
          {
            // E.g. read GCS heartbeat and go into
            // comm lost mode if timer times out
          }
          break;

        case MAVLINK_MSG_ID_SYS_STATUS:  // #1: SYS_STATUS
          {
            /* Message decoding: PRIMITIVE
                  mavlink_msg_sys_status_decode(const mavlink_message_t* msg, mavlink_sys_status_t* sys_status)
            */
            //mavlink_message_t* msg;
            mavlink_sys_status_t sys_status;
            mavlink_msg_sys_status_decode(&msg, &sys_status);
            Serial.println("2-");
          }
          break;

        case MAVLINK_MSG_ID_PARAM_VALUE:  // #22: PARAM_VALUE
          {
            /* Message decoding: PRIMITIVE
                  mavlink_msg_param_value_decode(const mavlink_message_t* msg, mavlink_param_value_t* param_value)
            */
            //mavlink_message_t* msg;
            mavlink_param_value_t param_value;
            mavlink_msg_param_value_decode(&msg, &param_value);
            Serial.println("3-");
          }
          break;

        case MAVLINK_MSG_ID_RAW_IMU:  // #27: RAW_IMU
          {
            /* Message decoding: PRIMITIVE
                  static inline void mavlink_msg_raw_imu_decode(const mavlink_message_t* msg, mavlink_raw_imu_t* raw_imu)
            */
            mavlink_raw_imu_t raw_imu;
            mavlink_msg_raw_imu_decode(&msg, &raw_imu);
            Serial.println(raw_imu.zgyro);
          }
          break;

        case MAVLINK_MSG_ID_REQUEST_DATA_STREAM :  // #66
          {


          }
          break;

        case MAVLINK_MSG_ID_ATTITUDE:  // #30
          {
            /* Message decoding: PRIMITIVE
                  mavlink_msg_attitude_decode(const mavlink_message_t* msg, mavlink_attitude_t* attitude)
            */
            mavlink_attitude_t attitude;
            mavlink_msg_attitude_decode(&msg, &attitude);
            Serial.println("5-");
          }
          break;


        default:
          break;
      }
    }
  }
}

void rc_override(int mav_steer, int mav_speed) {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];

  mavlink_msg_rc_channels_override_pack(sysid, compid, &msg, 0, 0,
                                        mav_steer,
                                        mav_speed,
                                        65535, 65535, 65535, 65535, 65535, 65535);

  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  Serial1.write(buf, len);
}

I changed the target id, sys id. I've tried Mavlink1 and 2, different SERIAL2_BAUD. I am expecting to have an answer from the pixhawk in loop with the different msg.msgid. Now I have only 0 and 66. Heartbeat and request. enter image description here

Answer 1

you can actually get data streamed from pixhawk without sending any requests.

Setting the SRx_ parameters (and then rebooting the autopilot) will cause the autopilot to pro-actively send groups of messages to the ground station. (https://ardupilot.org/dev/docs/mavlink-requesting-data.html)

see if you can get any data after you set your SRx parameters.

BTW, as Hemanth Narayan mentioned, the mavlink.h library works only with mavlink 1. I tried mavlink 2, not data picked up.

Answer 2

I faced the same issue as well. The serial2 port in pixhawk is the TELEM2 port, make sure the order of pins is correctly connected. If you are using mavlink.h in Arduino, the old version of this library works with the mavlink1 protocol. The message id 0 implies you are getting the heartbeat. let me know if you need more information.