User Input

In the previous example we registered a callback for tick events. In this example, we will register callbacks for knob and button input, then use them to send MIDI CC messages and toggle an LED.

Create Application Files

mkdir cpu/src/apps/my-midi-knob
cp template_app.c cpu/src/apps/my-midi-knob/my_midi_knob.c

Initialise Application

In the app_init() function, we register callbacks for knob and button input events.

t_status app_init(void) {

    t_status status = ERROR;

    ft_register_panel_callback(KNOB_EVENT, _knob_callback);
    ft_register_panel_callback(BUTTON_EVENT, _button_callback);

    status =  SUCCESS;
    return status
}

Define Run Behaviour

Our app_run() function is very similar to the previous example. If a flag is set, we toggle an LED and clear the flag. The flag will be set in our button callback below. In this example, we toggle the [Play] button LED.

void app_run(void) {

    if (g_toggle_led) {
        ft_toggle_led(LED_PLAY);

        g_toggle_led = false;
    }
}

Define Knob Callback

The knob callback takes 2 arguments and returns nothing. The first argument is the index of the knob and the second is it's value. In this example, we send a MIDI CC message on channel 1, with CC number equal to knob index and CC value equal to half knob value. The panel MCU sends 8 bit unsigned values in the range 0...255 for knobs, so we right shift by 1 for MIDI CC values.

void _knob_callback(uint8_t index, uint8_t value) {

    ft_send_cc(0, index, value >> 1);
}

Define Button Callback

The button callback prototype is similar to the knob callback. It takes 2 arguments, button index and button state, and returns nothing. In this example, we parse the button index and test the button state. When the [Play] button is depressed we set a flag to toggle it's LED. We ignore when the [Play] button is released.

void _button_callback(uint8_t index, bool state) {

    switch (index) {

    case BUTTON_PLAY:

        if (state == 1) {
            g_toggle_led == true;
        }
        break;

    default:
        break;
    }
}

Build and Run the Application

Build the application by passing midi-knob to make in the APP environment variable:

make clean && make APP=my-midi-knob

Then run the application using GDB:

cd cpu && arm-none-eabi-gdb

The commands in cpu/.gdbinit should take care of attaching to the debugger's GDB server and loading the ELF.

If all is well, moving any of the knobs should send MIDI CC messages. Pressing the [Play] button should toggle it's LED.

Things to Try

Try remapping the CC number to something other than the knob index.

Try sending CC messages for button events.

Try sending note messages for trigger pad input.

Next Steps

In the next example, we will see how to use the display.

midi-knob.c

// Freetribe: midi-knob
// License: AGPL-3.0-or-later

/*----- Includes -----------------------------------------------------*/

#include "freetribe.h"

/*----- Macros and Definitions ---------------------------------------*/

#define BUTTON_PLAY 0x2

/*----- Static variable definitions ----------------------------------*/

static bool g_toggle_led = false;

/*----- Extern variable definitions ----------------------------------*/

/*----- Static function prototypes -----------------------------------*/

void _knob_callback(uint8_t index, uint8_t value);
void _button_callback(uint8_t index, bool state);

/*----- Extern function implementations ------------------------------*/

/**
 * @brief   Initialise application.
 */
t_status app_init(void) {

    t_status status = ERROR;

    ft_register_panel_callback(KNOB_EVENT, _knob_callback);
    ft_register_panel_callback(BUTTON_EVENT, _button_callback);

    status = SUCCESS;
    return status;
}

/**
 * @brief   Run application.
 */
void app_run(void) {

    if (g_toggle_led) {
        ft_toggle_led(LED_PLAY);

        g_toggle_led = false;
    }
}

/*----- Static function implementations ------------------------------*/

/**
 * @brief   Callback triggered by panel knob events.
 */
void _knob_callback(uint8_t index, uint8_t value) {

    ft_send_cc(0, index, value >> 1);
}

/**
 * @brief   Callback triggered by panel button events.
 */
void _button_callback(uint8_t index, bool state) {

    switch (index) {

    case BUTTON_PLAY:
        if (state == 1) {
            g_toggle_led = true;
        }
        break;
    }
}

/*----- End of file --------------------------------------------------*/