How to use a wireless controller on the Google Coral Dev Board?

Question

With the Jetson Nano I connected a PS4 controller via bluetooth and the device showed up under /dev/input/js0. However when I connect the controller via bluetooth to my Coral board, I am seeing nothing at that location, maybe because of Mendel instead of Ubuntu? What is the recommended way to connect a PS4 controller and access it from C++? Is there a different joystick I should use?

Answer 1

After doing some research I learned about the difference between joydev and evdev on linux. It seems my PS4 controller showed up as a joydev device on the Jetson, whereas on the Coral running Mendel it showed up as an evdev device. I found some example C++ code for evdev devices from Croepha / David Butler here: https://handmade.network/forums/t/3673-modern_way_to_read_gamepad_input_with_c_on_linux

I modified this code for the PS4 controller like this:

void runJoystick() {
    auto gamepad = open("/dev/input/event4", O_RDONLY | O_NONBLOCK); //todo use /proc/bus/input/devices instead
    assert(gamepad != -1);
    std::cout << "Running joystick" << std::endl;

    while (m_still_running) {
        struct input_event events[8];  // 8 events per frame is pretty extreme, more like 1 or 2, sometimes as high as 4
        auto r1 = read(gamepad, events, sizeof events);
        if (r1 != -1) {
            int new_event_count = r1 / sizeof(struct input_event);
            for (int evi = 0; evi < new_event_count; evi++) {
                auto& ev = events[evi];

                switch (ev.type) {
                    case EV_ABS: {
                        switch (ev.code) {
                            case ABS_X: {  // left x
                                // std::cout << "type " << ev.code << "value:" << ev.value << std::endl;
                            } break;
                            case ABS_Y: {  // left y
                                // std::cout << "type " << ev.code << "value:" << ev.value << std::endl;
                            } break;
                            case ABS_Z: {  // right x
                                // std::cout << "type " << ev.code << "value:" << ev.value << std::endl;
                            } break;
                            case ABS_RZ: {  // right y
                                // std::cout << "type " << ev.code << "value:" << ev.value << std::endl;
                            } break;
                        }
                    } break;
                    case EV_KEY: {
                        switch (ev.code) {
                            case BTN_A: {  // square
                                std::cout << "Square ";
                            } break;
                            case BTN_B: {  // x
                                std::cout << "X ";
                            } break;
                            case BTN_C: {  // circle
                                std::cout << "Circle ";
                            } break;
                            case BTN_X: {  // triangle
                                std::cout << "Triangle ";
                            } break;
                        }

                        if (ev.value) {
                            std::cout << "Pressed " << std::endl;
                        } else {
                            std::cout << "Released " << std::endl;
                        }

                    } break;
                }
            }
        }

        assert(r1 != -1 || errno == EWOULDBLOCK || errno == EAGAIN);
        std::this_thread::sleep_for(std::chrono::milliseconds(20));
    }
}