GCS_MAVLink: Ground Station Communication Library

// Preferred — macro handles severity and format string
GCS_SEND_TEXT(MAV_SEVERITY_INFO, "Calibration complete, offset %.2f", offset);

// Also available on the singleton (thread-safe, queued)
gcs().send_text(MAV_SEVERITY_WARNING, "Battery low: %d%%", pct);

// Per-channel variant
gcs().chan(0)->send_named_float("MY_SENSOR", value);

// Broadcast to all channels
gcs().send_named_float("MY_SENSOR", value);

mavlink_my_msg_t pkt {};
pkt.value = 42;
GCS_MAVLINK::send_to_components(
    MAVLINK_MSG_ID_MY_MSG,
    (const char *)&pkt,
    sizeof(pkt));

GCS_MAVLINK::routing.check_and_forward()
  ↓ learns the sender's route
  ↓ looks up target sysid/compid
  ↓ forwards to the correct channel (or broadcasts if target is 0)
  → returns true if the message should also be processed locally

// Signing is enabled or disabled per-channel via the options bitmask.
// Bit 0 of SERIALn_OPTIONS disables signing on a specific port.
enum class Option : uint16_t {
    MAVLINK2_SIGNING_DISABLED = (1U << 0),
    NO_FORWARD                = (1U << 1),
    NOSTREAMOVERRIDE          = (1U << 2),
    FORWARD_BAD_CRC           = (1U << 3),
};

// Called internally when GPS time is valid:
GCS_MAVLINK::update_signing_timestamp(timestamp_usec);

// In your vehicle's GCS subclass (e.g. GCS_MAVLINK_Copter):
MAV_RESULT GCS_MAVLINK_MyVehicle::handle_command_int_packet(
    const mavlink_command_int_t &packet,
    const mavlink_message_t &msg)
{
    switch (packet.command) {
    case MAV_CMD_DO_MY_THING:
        return handle_my_thing(packet);
    default:
        return GCS_MAVLINK::handle_command_int_packet(packet, msg);
    }
}

void GCS_MAVLINK_MyVehicle::handle_message(const mavlink_message_t &msg)
{
    switch (msg.msgid) {
    case MAVLINK_MSG_ID_MY_CUSTOM_MSG: {
        mavlink_my_custom_msg_t pkt;
        mavlink_msg_my_custom_msg_decode(&msg, &pkt);
        // process pkt ...
        break;
    }
    default:
        GCS_MAVLINK::handle_message(msg);   // call base for all other IDs
        break;
    }
}

// Inside a GCS_MAVLINK method — returns false if no space:
if (!HAVE_PAYLOAD_SPACE(chan, ATTITUDE)) {
    return false;
}
mavlink_msg_attitude_send(chan, ...);

// Shorthand macro that returns false from the current function:
CHECK_PAYLOAD_SIZE(ATTITUDE);
mavlink_msg_attitude_send(chan, ...);

// ---- Sending a status text and a named float ----

void MyLibrary::update()
{
    if (some_condition) {
        // Broadcast to all GCS channels
        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "MyLib: event triggered (val=%.1f)", _value);
        gcs().send_named_float("MYLIB_VAL", _value);
    }
}

// ---- Handling a custom COMMAND_INT in a vehicle subclass ----

MAV_RESULT GCS_MAVLINK_MyVehicle::handle_command_int_packet(
    const mavlink_command_int_t &packet,
    const mavlink_message_t &msg)
{
    switch (packet.command) {
    case MAV_CMD_USER_1:
        // packet.param1 .. packet.param7 hold the command arguments
        if (!mylib.do_action((uint8_t)packet.param1)) {
            return MAV_RESULT_FAILED;
        }
        return MAV_RESULT_ACCEPTED;

    default:
        return GCS_MAVLINK::handle_command_int_packet(packet, msg);
    }
}