MAVLink Control

Main application with the "linear" sequences. Uses main standard input/output C header files, strings, as well as <interface.h> and <commands.h> defined headers.

int main(void){
    autopilot_intialize();

    #ifdef STM32F4

    // initialize LIS3DSH accelerometer
    lis3dsh_init();

    #endif

    serial_start();

    while (1) {
        commands();
    }

    return 0;
    }

1. autopilot_intialize()

MAVLink Control calls the autopilot_intialise() function first which is defined in interface.cpp. This function defines the necessary variables for the offboard control status, armed/disarmed status, and especially the target system, autopilot and companion IDs :

system_id    = 1; 
autopilot_id = 1; 
companion_id = 0;

2. lis3dsh_init()

If we aren't running on a nix system, (e.g the #ifdef STM32F4 is true, which is defined in the corresponding Makefile), we initialize the LIS3DSH accelerometer for the STM32F4-discovery board. Note : It's crucial that the USART and SPI configurations are initialized earlier in the program.

lis3dsh_init() calls spi_setup(), which configures the necessary GPIO, clocks, USART and SPI.

More on this in the separate chapter "LIS3DSH" which explains the functionnality of each method.

3. serial_start()

This function is defined in serial_port_stm32.cpp and serial_port_pc.cpp, depending on the hardware, it either starts and opens the necessary port on the nix system to communicate with the Pixhawk through USB/RS-232 Converter (FTDI Cable) or initialize the required USART, interrupts, and timer to achieve the same functionnality on the STM32F4-disovery board.

4. commands()

Commands () is simply a very basic scheduler in a while (1) loop that calls the needed function from commands.cpp. This scheduler enters the needed command then read a message structure(read_messages()), lock in the initial postion with autopilot_start(), writes a void message (autopilot_write_helper()) and then enters a switch and executes each command in a sequential fation.

void commands(void){
         operation(10);
        // operation_extended(10);
        // square_operation(7);
        // circle_operation(5);
        // automatic_takeoff(10);
        // flight_control_sequence(10);
        }

The switch command will depend on a Program_counter variable that, depending on configuartion, might either quit the program, or get stuck into an infinite loop, reading MAVLink messages.