[nRF52840][usbd_hid_composite] How to send data to Control EP in Linux?

[Haojz]

Hello Nordic experts,

I am doing SDK 15.3.0 usbd_hid_composite example and this is where I am: https://devzone.nordicsemi.com/f/nordic-q-a/50447/nrf52840-usbd_hid_composite-how-does-windows-transmit-caps-lock-state-to-the-device-without-output-endpoint/201751. I want to modified the code so that I can control the output letter from "g" to any letter by changing the output report/control EP(EP 0). I have done the Nordic nRF52840 side code, but I do not know how to send the data from Ubuntu to the output report or control EP. So my question is how do I send data to the Control EP in Linux so that I can change the default output letter "g" to other letter?

Modified code:

/**
 * Copyright (c) 2017 - 2019, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>

#include "nrf.h"
#include "nrf_drv_usbd.h"
#include "nrf_drv_clock.h"
#include "nrf_gpio.h"
#include "nrf_drv_power.h"

#include "app_timer.h"
#include "app_usbd.h"
#include "app_usbd_core.h"
#include "app_usbd_hid_mouse.h"
#include "app_usbd_hid_kbd.h"
#include "app_usbd_dummy.h"
#include "app_error.h"
#include "bsp.h"

#include "bsp_cli.h"
#include "nrf_cli.h"
#include "nrf_cli_uart.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

/**
 * @brief CLI interface over UART
 */
NRF_CLI_UART_DEF(m_cli_uart_transport, 0, 64, 16);
NRF_CLI_DEF(m_cli_uart,
            "uart_cli:~$ ",
            &m_cli_uart_transport.transport,
            '\r',
            4);

/**
 * @brief Enable USB power detection
 */
#ifndef USBD_POWER_DETECTION
#define USBD_POWER_DETECTION true
#endif

/**
 * @brief Enable HID mouse class
 */
#define CONFIG_HAS_MOUSE    1

/**
 * @brief Enable HID keyboard class
 */
#define CONFIG_HAS_KBD      1

/**
 * @brief Mouse button count
 */
#define CONFIG_MOUSE_BUTTON_COUNT 1//2

/**
 * @brief Mouse speed (value sent via HID when board button is pressed).
 */
#define CONFIG_MOUSE_MOVE_STEP (3)

/**
 * @brief Mouse move repeat time in milliseconds
 */
#define CONFIG_MOUSE_MOVE_TIME_MS (5)

/**
 * @brief Letter to be sent on LETTER button
 *
 * @sa BTN_KBD_LETTER
 */
uint8_t config_kbd_letter = APP_USBD_HID_KBD_G;
//#define CONFIG_KBD_LETTER APP_USBD_HID_KBD_G


/**
 * @brief Propagate SET_PROTOCOL command to other HID instance
 */
#define PROPAGATE_PROTOCOL  0


#define LED_CAPSLOCK       (BSP_BOARD_LED_0) /**< CAPSLOCK */
//#define LED_NUMLOCK        (BSP_BOARD_LED_1) /**< NUMLOCK */
#define LED_HID_REP        (BSP_BOARD_LED_1)//2) /**< Changes its state if any HID report was received or transmitted */
#define LED_USB_START      (BSP_BOARD_LED_2)//3) /**< The USBD library has been started and the bus is not in SUSPEND state */

//#define BTN_MOUSE_X_POS   0
#define BTN_MOUSE_LEFT     0//1
//#define BTN_KBD_SHIFT      2
#define BTN_KBD_LETTER     1//3

/**
 * @brief Additional key release events
 *
 * This example needs to process release events of used buttons
 */
enum {
    BSP_USER_EVENT_RELEASE_0 = BSP_EVENT_KEY_LAST + 1, /**< Button 0 released */
    BSP_USER_EVENT_RELEASE_1,                          /**< Button 1 released */
    BSP_USER_EVENT_RELEASE_2,                          /**< Button 2 released */
    BSP_USER_EVENT_RELEASE_3,                          /**< Button 3 released */
    BSP_USER_EVENT_RELEASE_4,                          /**< Button 4 released */
    BSP_USER_EVENT_RELEASE_5,                          /**< Button 5 released */
    BSP_USER_EVENT_RELEASE_6,                          /**< Button 6 released */
    BSP_USER_EVENT_RELEASE_7,                          /**< Button 7 released */
};

/**
 * @brief USB composite interfaces
 */
#define APP_USBD_INTERFACE_MOUSE 0
#define APP_USBD_INTERFACE_KBD   1

/**
 * @brief User event handler, HID mouse
 */
static void hid_mouse_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                      app_usbd_hid_user_event_t event);

/**
 * @brief User event handler, HID keyboard
 */
static void hid_kbd_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                    app_usbd_hid_user_event_t event);

/*lint -save -e26 -e64 -e123 -e505 -e651*/

/**
 * @brief Global HID mouse instance
 */
APP_USBD_HID_MOUSE_GLOBAL_DEF(m_app_hid_mouse,
                              APP_USBD_INTERFACE_MOUSE,
                              NRF_DRV_USBD_EPIN1,
                              CONFIG_MOUSE_BUTTON_COUNT,
                              hid_mouse_user_ev_handler,
                              APP_USBD_HID_SUBCLASS_BOOT
);

APP_USBD_DUMMY_GLOBAL_DEF(m_app_mouse_dummy, APP_USBD_INTERFACE_MOUSE);

/**
 * @brief Global HID keyboard instance
 */
APP_USBD_HID_KBD_GLOBAL_DEF(m_app_hid_kbd,
                            APP_USBD_INTERFACE_KBD,
                            NRF_DRV_USBD_EPIN2,
                            hid_kbd_user_ev_handler,
                            APP_USBD_HID_SUBCLASS_BOOT
);
APP_USBD_DUMMY_GLOBAL_DEF(m_app_kbd_dummy, APP_USBD_INTERFACE_KBD);

/*lint -restore*/

/**
 * @brief Timer to repeat mouse move
 */
APP_TIMER_DEF(m_mouse_move_timer);


static void kbd_status(void)
{
//    if(app_usbd_hid_kbd_led_state_get(&m_app_hid_kbd, APP_USBD_HID_KBD_LED_NUM_LOCK))
//    {
//        bsp_board_led_on(LED_NUMLOCK);
//    }
//    else
//    {
//        bsp_board_led_off(LED_NUMLOCK);
//    }

    if(app_usbd_hid_kbd_led_state_get(&m_app_hid_kbd, APP_USBD_HID_KBD_LED_CAPS_LOCK))
    {
        bsp_board_led_on(LED_CAPSLOCK);
    }
    else
    {
        bsp_board_led_off(LED_CAPSLOCK);
    }
}

/**
 * @brief Class specific event handler.
 *
 * @param p_inst    Class instance.
 * @param event     Class specific event.
 * */
static void hid_mouse_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                      app_usbd_hid_user_event_t event)
{
    UNUSED_PARAMETER(p_inst);
    switch (event) {
        case APP_USBD_HID_USER_EVT_OUT_REPORT_READY:
            /* No output report defined for HID mouse.*/
            ASSERT(0);
            break;
        case APP_USBD_HID_USER_EVT_IN_REPORT_DONE:
            bsp_board_led_invert(LED_HID_REP);
            break;
        case APP_USBD_HID_USER_EVT_SET_BOOT_PROTO:
            UNUSED_RETURN_VALUE(hid_mouse_clear_buffer(p_inst));
#if PROPAGATE_PROTOCOL
            hid_kbd_on_set_protocol(&m_app_hid_kbd, APP_USBD_HID_USER_EVT_SET_BOOT_PROTO);
#endif
            break;
        case APP_USBD_HID_USER_EVT_SET_REPORT_PROTO:
            UNUSED_RETURN_VALUE(hid_mouse_clear_buffer(p_inst));
#if PROPAGATE_PROTOCOL
            hid_kbd_on_set_protocol(&m_app_hid_kbd, APP_USBD_HID_USER_EVT_SET_REPORT_PROTO);
#endif
            break;
        default:
            break;
    }
}

/**
 * @brief Class specific event handler.
 *
 * @param p_inst    Class instance.
 * @param event     Class specific event.
 * */
//const void * app_usbd_hid_kbd_out_report_get(app_usbd_hid_kbd_t const * p_kbd,
//                                             size_t * p_size);

size_t size;
uint8_t *report;
uint8_t LED;

static void hid_kbd_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                    app_usbd_hid_user_event_t event)
{
    UNUSED_PARAMETER(p_inst);
    switch (event) {
        case APP_USBD_HID_USER_EVT_OUT_REPORT_READY:
            /* Only one output report IS defined for HID keyboard class. Update LEDs state. */
						//self-added
						report = (uint8_t *) app_usbd_hid_kbd_out_report_get(&m_app_hid_kbd, &size);
						LED = report[1];
						if (LED == 0) config_kbd_letter = APP_USBD_HID_KBD_A;
						else if (LED == 1) config_kbd_letter = APP_USBD_HID_KBD_B;
						else if (LED == 2) config_kbd_letter = APP_USBD_HID_KBD_C;
						else if (LED == 3) config_kbd_letter = APP_USBD_HID_KBD_D;
						else if (LED == 4) config_kbd_letter = APP_USBD_HID_KBD_E;
						else if (LED == 5) config_kbd_letter = APP_USBD_HID_KBD_F;
						else if (LED == 6) config_kbd_letter = APP_USBD_HID_KBD_G;
						else if (LED == 7) config_kbd_letter = APP_USBD_HID_KBD_H;
						else if (LED == 8) config_kbd_letter = APP_USBD_HID_KBD_I;
						else if (LED == 9) config_kbd_letter = APP_USBD_HID_KBD_J;
						else if (LED == 10) config_kbd_letter = APP_USBD_HID_KBD_K;
						else if (LED == 11) config_kbd_letter = APP_USBD_HID_KBD_L;
						else if (LED == 12) config_kbd_letter = APP_USBD_HID_KBD_M;
						else if (LED == 13) config_kbd_letter = APP_USBD_HID_KBD_N;
						else if (LED == 14) config_kbd_letter = APP_USBD_HID_KBD_O;
						else if (LED == 15) config_kbd_letter = APP_USBD_HID_KBD_P;
						else if (LED == 16) config_kbd_letter = APP_USBD_HID_KBD_Q;
						else if (LED == 17) config_kbd_letter = APP_USBD_HID_KBD_R;
						else if (LED == 18) config_kbd_letter = APP_USBD_HID_KBD_S;
						else if (LED == 19) config_kbd_letter = APP_USBD_HID_KBD_T;
						else if (LED == 20) config_kbd_letter = APP_USBD_HID_KBD_U;
						else if (LED == 21) config_kbd_letter = APP_USBD_HID_KBD_V;
						else if (LED == 22) config_kbd_letter = APP_USBD_HID_KBD_W;
						else if (LED == 23) config_kbd_letter = APP_USBD_HID_KBD_X;
						else if (LED == 24) config_kbd_letter = APP_USBD_HID_KBD_Y;
						else if (LED == 25) config_kbd_letter = APP_USBD_HID_KBD_Z;
						else config_kbd_letter = APP_USBD_HID_KBD_G;	
            bsp_board_led_invert(LED_HID_REP);
            kbd_status();
            break;
        case APP_USBD_HID_USER_EVT_IN_REPORT_DONE:
            bsp_board_led_invert(LED_HID_REP);
            break;
        case APP_USBD_HID_USER_EVT_SET_BOOT_PROTO:
            UNUSED_RETURN_VALUE(hid_kbd_clear_buffer(p_inst));
#if PROPAGATE_PROTOCOL
            hid_mouse_on_set_protocol(&m_app_hid_mouse, APP_USBD_HID_USER_EVT_SET_BOOT_PROTO);
#endif
            break;
        case APP_USBD_HID_USER_EVT_SET_REPORT_PROTO:
            UNUSED_RETURN_VALUE(hid_kbd_clear_buffer(p_inst));
#if PROPAGATE_PROTOCOL
            hid_mouse_on_set_protocol(&m_app_hid_mouse, APP_USBD_HID_USER_EVT_SET_REPORT_PROTO);
#endif
            break;
        default:
            break;
    }
}


/**
 * @brief USBD library specific event handler.
 *
 * @param event     USBD library event.
 * */
static void usbd_user_ev_handler(app_usbd_event_type_t event)
{
    switch (event)
    {
        case APP_USBD_EVT_DRV_SOF:
            break;
        case APP_USBD_EVT_DRV_SUSPEND:
            app_usbd_suspend_req(); // Allow the library to put the peripheral into sleep mode
            bsp_board_leds_off();
            break;
        case APP_USBD_EVT_DRV_RESUME:
            bsp_board_led_on(LED_USB_START);
            kbd_status(); /* Restore LED state - during SUSPEND all LEDS are turned off */
            break;
        case APP_USBD_EVT_STARTED:
            bsp_board_led_on(LED_USB_START);
            break;
        case APP_USBD_EVT_STOPPED:
            app_usbd_disable();
            bsp_board_leds_off();
            break;
        case APP_USBD_EVT_POWER_DETECTED:
            NRF_LOG_INFO("USB power detected");

            if (!nrf_drv_usbd_is_enabled())
            {
                app_usbd_enable();
            }
            break;
        case APP_USBD_EVT_POWER_REMOVED:
            NRF_LOG_INFO("USB power removed");
            app_usbd_stop();
            break;
        case APP_USBD_EVT_POWER_READY:
            NRF_LOG_INFO("USB ready");
            app_usbd_start();
            break;
        default:
            break;
    }
}


static void mouse_move_timer_handler(void * p_context)
{
    UNUSED_PARAMETER(p_context);
    UNUSED_RETURN_VALUE(app_usbd_hid_mouse_x_move(&m_app_hid_mouse, CONFIG_MOUSE_MOVE_STEP));
}

static void bsp_event_callback(bsp_event_t ev)
{
    switch ((unsigned int)ev)
    {
//        case CONCAT_2(BSP_EVENT_KEY_, BTN_MOUSE_X_POS):
//            UNUSED_RETURN_VALUE(app_usbd_hid_mouse_x_move(&m_app_hid_mouse, CONFIG_MOUSE_MOVE_STEP));
//            UNUSED_RETURN_VALUE(app_timer_start(m_mouse_move_timer, APP_TIMER_TICKS(CONFIG_MOUSE_MOVE_TIME_MS), NULL));
//            break;
//        case CONCAT_2(BSP_USER_EVENT_RELEASE_, BTN_MOUSE_X_POS):
//            UNUSED_RETURN_VALUE(app_timer_stop(m_mouse_move_timer));
//            break;

        case CONCAT_2(BSP_EVENT_KEY_, BTN_MOUSE_LEFT):
            UNUSED_RETURN_VALUE(app_usbd_hid_mouse_button_state(&m_app_hid_mouse, 0, true));
            break;
        case CONCAT_2(BSP_USER_EVENT_RELEASE_, BTN_MOUSE_LEFT):
            UNUSED_RETURN_VALUE(app_usbd_hid_mouse_button_state(&m_app_hid_mouse, 0, false));
            break;

//        case CONCAT_2(BSP_EVENT_KEY_, BTN_KBD_SHIFT):
//            UNUSED_RETURN_VALUE(app_usbd_hid_kbd_modifier_state_set(&m_app_hid_kbd, APP_USBD_HID_KBD_MODIFIER_LEFT_SHIFT, true));
//            break;
//        case CONCAT_2(BSP_USER_EVENT_RELEASE_, BTN_KBD_SHIFT):
//            UNUSED_RETURN_VALUE(app_usbd_hid_kbd_modifier_state_set(&m_app_hid_kbd, APP_USBD_HID_KBD_MODIFIER_LEFT_SHIFT, false));
//            break;

        case CONCAT_2(BSP_EVENT_KEY_, BTN_KBD_LETTER):
            UNUSED_RETURN_VALUE(app_usbd_hid_kbd_key_control(&m_app_hid_kbd, config_kbd_letter, true));//CONFIG_KBD_LETTER, true));
            break;
        case CONCAT_2(BSP_USER_EVENT_RELEASE_, BTN_KBD_LETTER):
            UNUSED_RETURN_VALUE(app_usbd_hid_kbd_key_control(&m_app_hid_kbd, config_kbd_letter, false));//CONFIG_KBD_LETTER, false));
            break;

        default:
            return; // no implementation needed
    }
}

/**
 * @brief Auxiliary internal macro
 *
 * Macro used only in @ref init_bsp to simplify the configuration
 */
#define INIT_BSP_ASSIGN_RELEASE_ACTION(btn)                      \
    APP_ERROR_CHECK(                                             \
        bsp_event_to_button_action_assign(                       \
            btn,                                                 \
            BSP_BUTTON_ACTION_RELEASE,                           \
            (bsp_event_t)CONCAT_2(BSP_USER_EVENT_RELEASE_, btn)) \
    )

static void init_bsp(void)
{
    ret_code_t ret;
    ret = bsp_init(BSP_INIT_BUTTONS, bsp_event_callback);
    APP_ERROR_CHECK(ret);

//    INIT_BSP_ASSIGN_RELEASE_ACTION(BTN_MOUSE_X_POS);
    INIT_BSP_ASSIGN_RELEASE_ACTION(BTN_MOUSE_LEFT );
//    INIT_BSP_ASSIGN_RELEASE_ACTION(BTN_KBD_SHIFT  );
    INIT_BSP_ASSIGN_RELEASE_ACTION(BTN_KBD_LETTER );

    /* Configure LEDs */
    bsp_board_init(BSP_INIT_LEDS);
}

static void init_cli(void)
{
    ret_code_t ret;
    ret = bsp_cli_init(bsp_event_callback);
    APP_ERROR_CHECK(ret);
    nrf_drv_uart_config_t uart_config = NRF_DRV_UART_DEFAULT_CONFIG;
    uart_config.pseltxd = TX_PIN_NUMBER;
    uart_config.pselrxd = RX_PIN_NUMBER;
    uart_config.hwfc    = NRF_UART_HWFC_DISABLED;
    ret = nrf_cli_init(&m_cli_uart, &uart_config, true, true, NRF_LOG_SEVERITY_INFO);
    APP_ERROR_CHECK(ret);
    ret = nrf_cli_start(&m_cli_uart);
    APP_ERROR_CHECK(ret);
}

int main(void)
{
    ret_code_t ret;
    static const app_usbd_config_t usbd_config = {
        .ev_state_proc = usbd_user_ev_handler,
    };

    ret = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(ret);

    ret = nrf_drv_clock_init();
    APP_ERROR_CHECK(ret);

    nrf_drv_clock_lfclk_request(NULL);
    while(!nrf_drv_clock_lfclk_is_running())
    {
        /* Just waiting */
    }

    ret = app_timer_init();
    APP_ERROR_CHECK(ret);

    ret = app_timer_create(&m_mouse_move_timer, APP_TIMER_MODE_REPEATED, mouse_move_timer_handler);
    APP_ERROR_CHECK(ret);

    init_bsp();
    init_cli();

    ret = app_usbd_init(&usbd_config);
    APP_ERROR_CHECK(ret);

    app_usbd_class_inst_t const * class_inst_mouse;
#if CONFIG_HAS_MOUSE
    class_inst_mouse = app_usbd_hid_mouse_class_inst_get(&m_app_hid_mouse);
#else
    class_inst_mouse = app_usbd_dummy_class_inst_get(&m_app_mouse_dummy);
#endif
    ret = app_usbd_class_append(class_inst_mouse);
    APP_ERROR_CHECK(ret);

    app_usbd_class_inst_t const * class_inst_kbd;
#if CONFIG_HAS_KBD
    class_inst_kbd = app_usbd_hid_kbd_class_inst_get(&m_app_hid_kbd);
#else
    class_inst_kbd = app_usbd_dummy_class_inst_get(&m_app_kbd_dummy);
#endif
    ret = app_usbd_class_append(class_inst_kbd);
    APP_ERROR_CHECK(ret);

    NRF_LOG_INFO("USBD HID composite example started.");
    
    if (USBD_POWER_DETECTION)
    {
        ret = app_usbd_power_events_enable();
        APP_ERROR_CHECK(ret);
    }
    else
    {
        NRF_LOG_INFO("No USB power detection enabled\r\nStarting USB now");

        app_usbd_enable();
        app_usbd_start();
    }

    while (true)
    {
        while (app_usbd_event_queue_process())
        {
            /* Nothing to do */
        }
        nrf_cli_process(&m_cli_uart);

        UNUSED_RETURN_VALUE(NRF_LOG_PROCESS());
        /* Sleep CPU only if there was no interrupt since last loop processing */
        __WFE();
    }
}

Thank you for your support in advance and I look forward to hearing from you.

Kind regards,

Louis

[Haojz]

I found some code online using LIBUSB(C++) to write data to control EP. Here is the code: 

#include <iostream>
#include <string>
#include <libusb-1.0/libusb.h>

#define LIBUSB_ENDPOINT_IN 0x81
#define LIBUSB_ENDPOINT_OUT 0x1
using namespace std;

int main() {
	libusb_device **devs; //pointer to pointer of device, used to retrieve a list of devices
	libusb_device_handle *dev_handle; //a device handle
	libusb_context *ctx = NULL; //a libusb session
	int r; //for return values
	ssize_t cnt; //holding number of devices in list
	r = libusb_init(&ctx); //initialize the library for the session we just declared
	if(r < 0) {
		cout<<"Init Error "<<r<<endl; //there was an error
		return 1;
	}
	libusb_set_debug(ctx, 3); //set verbosity level to 3, as suggested in the documentation

	cnt = libusb_get_device_list(ctx, &devs); //get the list of devices
	if(cnt < 0) {
		cout<<"Get Device Error"<<endl; //there was an error
		return 1;
	}
	cout<<cnt<<" Devices in list."<<endl;

	dev_handle = libusb_open_device_with_vid_pid(ctx, 0x1915, 0x520B); //these are vendorID and productID I found for my usb device
	if(dev_handle == NULL)
		cout<<"Cannot open device"<<endl;
	else
		cout<<"Device Opened"<<endl;
	libusb_free_device_list(devs, 1); //free the list, unref the devices in it

	unsigned char *data = new unsigned char[4]; //data to write
	data[0]='1';data[1]='1';data[2]='1';data[3]='1'; //some dummy values // '1'=0x31

	int actual; //used to find out how many bytes were written
	if(libusb_kernel_driver_active(dev_handle, 0) == 1) { //find out if kernel driver is attached
		cout<<"Kernel Driver Active"<<endl;
		if(libusb_detach_kernel_driver(dev_handle, 0) == 0) //detach it
			cout<<"Kernel Driver Detached!"<<endl;
	}
	r = libusb_claim_interface(dev_handle, 0); //claim interface 0 (the first) of device (mine had jsut 1)
  if(r < 0) {
		cout<<"Cannot Claim Interface"<<endl;
		return 1;
	}

	cout<<"Claimed Interface"<<endl;

	// cout<<"Data->"<<data<<"<-"<<endl; //just to see the data we want to write : abcd
	cout<<"Writing Data..."<<endl;
	//r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_OUT, data, 4, &actual, 0); //write to OUT EP
	//r = libusb_bulk_transfer(dev_handle, LIBUSB_ENDPOINT_IN, data, 4, &actual, 0); //listen to IN EP
	actual = libusb_control_transfer(dev_handle, 0x21, 0x9, 0x200, 0, data, 4, 5000); //write to CONTROL EP

  cout<<"Data:";
  for(unsigned int i = 0; i < 4; i++){
    cout<<data[i]<<endl;
  }
  cout<<"actual: "<<actual<<endl;


	if(r == 0 && actual == 4) //we wrote the 4 bytes successfully
		cout<<"Writing Successful!"<<endl;
	else
		cout<<"Write Error"<<endl;

	r = libusb_release_interface(dev_handle, 0); //release the claimed interface
	if(r!=0) {
		cout<<"Cannot Release Interface"<<endl;
		return 1;
	}
	cout<<"Released Interface"<<endl;

	libusb_close(dev_handle); //close the device we opened
	libusb_exit(ctx); //needs to be called to end the

	delete[] data; //delete the allocated memory for data
	return 0;
}

However, when I write the data to CONTROL EP, I got the return value of "actual" -9, which means LIBUSB_PIPE_ERROR, and the writing is failed. Does anyone know how to fix this problem? or other way to write data to CONTROL EP?

[ovrebekk]

Hi

There are several odd things in your code. 

First off, in the APP_USBD_HID_USER_EVT_OUT_REPORT_READY handler you are reading out a single byte of data, yet you are assigning report[1] to the LED variable?

report[1] returns the second byte in the 'array', I would expect report[0] to return the correct byte. 

Also, on the Linux side it appears you are sending 4 bytes rather than 1, this won't work if the report descriptor sets up a 1 byte out report. 

Best regards
Torbjørn

[Haojz]

Hello Torbjørn,

Thank you for your reply and kind support.

ovrebekk said:

First off, in the APP_USBD_HID_USER_EVT_OUT_REPORT_READY handler you are reading out a single byte of data, yet you are assigning report[1] to the LED variable?

ovrebekk said:

report[1] returns the second byte in the 'array', I would expect report[0] to return the correct byte. 

I did this by following the suggestions in https://devzone.nordicsemi.com/f/nordic-q-a/50447/nrf52840-usbd_hid_composite-how-does-windows-transmit-caps-lock-state-to-the-device-without-output-endpoint/201751, and I verified this in Keil debug mode - it is correct: I do not know why but for CONTROL EP case(compare to OUT EP case), the data start from report[1] (whereas for OUT EP it indeed starts from report[0]).

ovrebekk said:

Also, on the Linux side it appears you are sending 4 bytes rather than 1, this won't work if the report descriptor sets up a 1 byte out report. 

Yes, you are right. After I changed the default descriptor to 4 bytes I can send the data to CONTROL EP successfully. 

Now, I would like to remove mouse and keyboard functions, only leaving the communication tunnels(IN EP & CONTROL EP/OUT EP) to transmit some data and execute some control commands from linux side. However, after I removed the mouse & keyboard things, the code stops to work(It is too complicated to modify it). Do you have any clear code only for HID USB communication via endpoints or any other suggestion to implement this target?

Thank you for your kind support again and I look forward to hearing from you soon.

Kind regards,

Louis

[ovrebekk]

Hi Louis

If you don't need any standard HID behavior, why don't you just set up a normal BLE connection with a proprietary GATT service?

Then you have full control over the data that you can send, and can shape the service according to your requirements. 

It seems overkill to use HID over GATT if you don't really need HID compatibility. 

Best regards
Torbjørn

[Haojz]

Hi Torbjørn,

ovrebekk said:

If you don't need any standard HID behavior, why don't you just set up a normal BLE connection with a proprietary GATT service?

Is BLE using USB to communicate? I do not want to use Bluetooth to communicate. I want to use just USB to send and receive data between host and nRF board.