Creating Custom Mavlink Message

README.md

Creating a Custom Mavlink Message

Download the Mavlink Toolchain

git clone https://github.com/mavlink/mavlink.git

Create a message defintion

Create a file named custom.xml with these contents:

<?xml version="1.0"?>
<mavlink>
  <messages>
    <message id="0" name="MY_CUSTOM_MSG">
      <description>My Custom Message</description>
      <field type="char[10]" name="sensor_name">Sensor Name</field>
      <field type="uint8_t" name="sensor_id">Sensor ID</field>
      <field type="double" name="sensor_value">Sensor Value</field>
    </message>
  </messages>
</mavlink>

If you want more examples you can check out the examples in the directory message_defintions/v1.0

Generate source code for the new messages

Open the mavgenerate.py program inside the MAVLink toolchain:

./mavgenerate.py

• In the XML field enter the file path for your custom message.
• In the Out field enter a directory name for where you want to put the genreated source code.
• In the Language field enter what language you'd like. For this README I will choose C.
• In the Protcol field enter what protocol you'd like. For this README I will choose 2.0.
• Click on "Generate"

Use the newly generated source code

Here is a simple example of message SENDER in C using the generated headers:

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <thread>

#include "mavlink/custom/mavlink.h"

int main()
{
  mavlink_message_t msg;
  uint16_t len;
  uint8_t buf[2041];
  ssize_t bytes_sent;
  int sock;
  struct sockaddr_in destAddr;

  // open a socket
  sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

  // set a destination address
  memset(&destAddr, 0, sizeof(destAddr));
  destAddr.sin_family = AF_INET;
  destAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  destAddr.sin_port = htons(14550);

  while(true) {
    // send custom message
    mavlink_msg_my_custom_msg_pack(2, 100, &msg, "sensor125", 125, 66.66);
    len = mavlink_msg_to_send_buffer(buf, &msg);
    bytes_sent = sendto(sock, buf, len, 0, (struct sockaddr*)&destAddr, sizeof(struct sockaddr_in));

    // wait a second
    std::this_thread::sleep_for(std::chrono::seconds(1));
  }

  return 0;
}

Here is a simple example of message RECEIVER in C using the generated headers:

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <thread>

#include "mavlink/custom/mavlink.h"

int main()
{
  mavlink_message_t msg;
  mavlink_status_t status;
  socklen_t clientLen;
  uint8_t buf[2041];
  ssize_t n;
  int sock;
  struct sockaddr_in bindAddr;
  struct sockaddr_in clientAddr;

  // open a socket
  sock = socket(AF_INET, SOCK_DGRAM, 0);

  // set bind address
  memset(&bindAddr, 0, sizeof(bindAddr));
  bindAddr.sin_family = AF_INET;
  bindAddr.sin_addr.s_addr = htonl(INADDR_ANY);
  bindAddr.sin_port = htons(14550);
  bind(sock, (struct sockaddr *) &bindAddr, sizeof(bindAddr));

  while(true) {
    n = recvfrom(sock, buf, 2041, 0, (struct sockaddr *) &clientAddr, &clientLen);
    if(n > 0) {
      for(int i = 0; i < n; ++i) {
        if (mavlink_parse_char(MAVLINK_COMM_0, buf[i], &msg, &status))
        {
          printf("Received packet: SYS: %d, COMP: %d, LEN: %d, MSG ID: %d\n", 
                 msg.sysid, msg.compid, msg.len, msg.msgid);
          if(msg.msgid == MAVLINK_MSG_ID_MY_CUSTOM_MSG) {
            double sensor_value = mavlink_msg_my_custom_msg_get_sensor_value(&msg);
            printf("It's a custom message: SENSOR VALUE: %f\n", sensor_value);
          }
        }
      }
    }
  }

  return 0;
}