USBREGSTATUS->OUTPUTRDY not set after reset with USB plugged in. And by extension, no APP_USBD_EVT_POWER_READY events are generated.

[GPL]

Hello,

Whenever we reset our custom board with the USB cable plugged in and powered, the NRF_POWER->USBREGSTATUS has a value of 1. It will not go to a value of 3 (OUTPUTRDY bit is set) until we re-plug the USB cable. Therefore, we only see the APP_USBD_EVT_POWER_DETECTED event, and not the  APP_USBD_EVT_POWER_READY event. This causes our device to not enumerate (as serial port) on the host PC. When we reset the device, and then plug in the cable everything works fine and we get the ready event.

Is this normal behavior, or is there something wrong with our initialization? See the relevant code below.

//In sdk_config.h
#define APP_USBD_CONFIG_POWER_EVENTS_PROCESS 1


int main(void)
{
    nrfx_err_t err_code;
    
    //......
    
    cli_init();
    usbd_init();
    ble_init();//Initialises the softdevice
    
    //......
    
    for(;;) {
        idle_state_handle();
        nrfx_wdt_channel_feed(main_loop_wdt_channel);
    }
}

void usbd_init(){
    ret_code_t ret;
    static const app_usbd_config_t usbd_config = {
        .ev_handler = app_usbd_event_execute,
        .ev_state_proc = usbd_user_ev_handler
    };
    ret = app_usbd_init(&usbd_config);
    APP_ERROR_CHECK(ret);

    app_usbd_class_inst_t const * class_cdc_acm =
            app_usbd_cdc_acm_class_inst_get(&nrf_cli_cdc_acm);
    ret = app_usbd_class_append(class_cdc_acm);
    APP_ERROR_CHECK(ret);
    
    ret = app_usbd_power_events_enable();
      APP_ERROR_CHECK(ret);
}

Let me know if I am missing some relevant information. 

[Sigurd]

Hi,

I don’t see anything wrong in the code you posted.

How does your usbd_user_ev_handler() code look like ?

Whenever we reset our custom board with the USB cable plugged in and powered

 There are several ways that can reset the board, pin-reset, nvic_systemreset(), watchdog reset, etc. How are you resetting the board?

What nRF5 SDK version are you using?

What IC revision of the nRF52840 are you testing on?

[GPL]

Hello, thank you for your time. Currently our main issue is that the events don't get fired after a System-off mode wake up from GPIO. 

Here's the code:

static void usbd_user_ev_handler(app_usbd_event_type_t event)
{
    switch (event)
    {
        case APP_USBD_EVT_DRV_SUSPEND:
        case APP_USBD_EVT_DRV_RESUME:
        case APP_USBD_EVT_STARTED:
            break;

        case APP_USBD_EVT_STOPPED:
            if(nrf_drv_usbd_is_enabled()){
                app_usbd_disable();
            }
            break;

        case APP_USBD_EVT_POWER_DETECTED:
            //also checked with log error to verify the proper severity level is not the problem
            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");
            g_usb_powered = false;//Application code
            if(nrf_drv_usbd_is_started()){
              app_usbd_stop();
            }
            APP_ERROR_CHECK(
                nrf_cli_stop(&cli_usb_handle)
            );
            break;

        case APP_USBD_EVT_POWER_READY:
            NRF_LOG_INFO("USB ready");
            g_usb_powered = true;//Application code
            if(!nrf_drv_usbd_is_started()){
                app_usbd_start();
            }
            APP_ERROR_CHECK(
              nrf_cli_start(&cli_usb_handle)
            );
            break;

        default:
            break;
    }
}

The SDK version is 16.0.0

I'm unsure how to determine the IC revision, I think below information is relevant.

To be clear, my end goal is to be able to enumerate the device as USB CDC ACM serial port after being woken from system off mode via GPIO with the USB cable plugged in.

[Sigurd]

Hi,

Have you been able to reproduce this on a nRF52840-DK ? or is it only your custom board that has this issue ?

I tried testing this with the usbd_ble_uart example on a nRF52840-DK, but it worked as expected, and I got both the APP_USBD_EVT_POWER_DETECTED and APP_USBD_EVT_POWER_READY event.

For reference, here is the modified usbd_ble_uart code I used. It will enter System Off mode after 5 seconds after start-up, and wakes up when button 1 / pin 11 is pressed.

/**
 * Copyright (c) 2017 - 2020, 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.
 *
 */
/** @file
 *
 * @defgroup usbd_ble_uart_example main.c
 * @{
 * @ingroup  usbd_ble_uart_example
 * @brief    USBD CDC ACM over BLE application main file.
 *
 * This file contains the source code for a sample application that uses the Nordic UART service
 * and USBD CDC ACM library.
 * This application uses the @ref srvlib_conn_params module.
 */

#include <stdint.h>
#include <string.h>
#include "nordic_common.h"
#include "nrf.h"
#include "ble_hci.h"
#include "ble_advdata.h"
#include "ble_advertising.h"
#include "ble_conn_params.h"
#include "nrf_sdh.h"
#include "nrf_sdh_soc.h"
#include "nrf_sdh_ble.h"
#include "nrf_ble_gatt.h"
#include "app_timer.h"
#include "ble_nus.h"
#include "app_uart.h"
#include "app_util_platform.h"
#include "bsp_btn_ble.h"

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

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

#include "app_error.h"
#include "app_util.h"
#include "app_usbd_core.h"
#include "app_usbd.h"
#include "app_usbd_string_desc.h"
#include "app_usbd_cdc_acm.h"
#include "app_usbd_serial_num.h"

#define LED_BLE_NUS_CONN (BSP_BOARD_LED_0)
#define LED_BLE_NUS_RX   (BSP_BOARD_LED_1)
#define LED_CDC_ACM_CONN (BSP_BOARD_LED_2)
#define LED_CDC_ACM_RX   (BSP_BOARD_LED_3)

#define LED_BLINK_INTERVAL 800

APP_TIMER_DEF(m_blink_ble);
APP_TIMER_DEF(m_blink_cdc);
APP_TIMER_DEF(m_system_off);

/**
 * @brief App timer handler for blinking the LEDs.
 *
 * @param p_context LED to blink.
 */
void blink_handler(void * p_context)
{
    bsp_board_led_invert((uint32_t) p_context);
}

void system_off_trigger(void * p_context)
{

    // Configure pin 11 /button1 with sense, so it can be used to wake-up the chip.
    nrf_gpio_cfg_sense_input(11, NRF_GPIO_PIN_PULLUP, NRF_GPIO_PIN_SENSE_LOW);

     NRF_POWER->SYSTEMOFF = POWER_SYSTEMOFF_SYSTEMOFF_Enter;
    __DSB();

    /* Solution for simulated System OFF in debug mode */
    while (true)
    {
        __WFE();
    }
}

#define ENDLINE_STRING "\r\n"

// USB DEFINES START
static void cdc_acm_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                    app_usbd_cdc_acm_user_event_t event);

#define CDC_ACM_COMM_INTERFACE  0
#define CDC_ACM_COMM_EPIN       NRF_DRV_USBD_EPIN2

#define CDC_ACM_DATA_INTERFACE  1
#define CDC_ACM_DATA_EPIN       NRF_DRV_USBD_EPIN1
#define CDC_ACM_DATA_EPOUT      NRF_DRV_USBD_EPOUT1

static char m_cdc_data_array[BLE_NUS_MAX_DATA_LEN];

/** @brief CDC_ACM class instance */
APP_USBD_CDC_ACM_GLOBAL_DEF(m_app_cdc_acm,
                            cdc_acm_user_ev_handler,
                            CDC_ACM_COMM_INTERFACE,
                            CDC_ACM_DATA_INTERFACE,
                            CDC_ACM_COMM_EPIN,
                            CDC_ACM_DATA_EPIN,
                            CDC_ACM_DATA_EPOUT,
                            APP_USBD_CDC_COMM_PROTOCOL_AT_V250);

// USB DEFINES END

// BLE DEFINES START
#define APP_BLE_CONN_CFG_TAG            1                                           /**< A tag identifying the SoftDevice BLE configuration. */

#define APP_FEATURE_NOT_SUPPORTED       BLE_GATT_STATUS_ATTERR_APP_BEGIN + 2        /**< Reply when unsupported features are requested. */

#define DEVICE_NAME                     "Nordic_USBD_BLE_UART"                      /**< Name of device. Will be included in the advertising data. */
#define NUS_SERVICE_UUID_TYPE           BLE_UUID_TYPE_VENDOR_BEGIN                  /**< UUID type for the Nordic UART Service (vendor specific). */

#define APP_BLE_OBSERVER_PRIO           3                                           /**< Application's BLE observer priority. You shouldn't need to modify this value. */

#define APP_ADV_INTERVAL                64                                          /**< The advertising interval (in units of 0.625 ms. This value corresponds to 40 ms). */
#define APP_ADV_DURATION                18000                                       /**< The advertising duration (180 seconds) in units of 10 milliseconds. */


#define MIN_CONN_INTERVAL               MSEC_TO_UNITS(20, UNIT_1_25_MS)             /**< Minimum acceptable connection interval (20 ms). Connection interval uses 1.25 ms units. */
#define MAX_CONN_INTERVAL               MSEC_TO_UNITS(75, UNIT_1_25_MS)             /**< Maximum acceptable connection interval (75 ms). Connection interval uses 1.25 ms units. */
#define SLAVE_LATENCY                   0                                           /**< Slave latency. */
#define CONN_SUP_TIMEOUT                MSEC_TO_UNITS(4000, UNIT_10_MS)             /**< Connection supervisory timeout (4 seconds). Supervision Timeout uses 10 ms units. */
#define FIRST_CONN_PARAMS_UPDATE_DELAY  APP_TIMER_TICKS(5000)                       /**< Time from initiating an event (connect or start of notification) to the first time sd_ble_gap_conn_param_update is called (5 seconds). */
#define NEXT_CONN_PARAMS_UPDATE_DELAY   APP_TIMER_TICKS(30000)                      /**< Time between each call to sd_ble_gap_conn_param_update after the first call (30 seconds). */
#define MAX_CONN_PARAMS_UPDATE_COUNT    3                                           /**< Number of attempts before giving up the connection parameter negotiation. */

#define DEAD_BEEF                       0xDEADBEEF                                  /**< Value used as error code on stack dump. Can be used to identify stack location on stack unwind. */

#define UART_TX_BUF_SIZE                256                                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE                256                                         /**< UART RX buffer size. */


BLE_NUS_DEF(m_nus, NRF_SDH_BLE_TOTAL_LINK_COUNT);                                   /**< BLE NUS service instance. */
NRF_BLE_GATT_DEF(m_gatt);                                                           /**< GATT module instance. */
BLE_ADVERTISING_DEF(m_advertising);                                                 /**< Advertising module instance. */

static uint16_t   m_conn_handle          = BLE_CONN_HANDLE_INVALID;                 /**< Handle of the current connection. */
static uint16_t   m_ble_nus_max_data_len = BLE_GATT_ATT_MTU_DEFAULT - 3;            /**< Maximum length of data (in bytes) that can be transmitted to the peer by the Nordic UART service module. */
static ble_uuid_t m_adv_uuids[]          =                                          /**< Universally unique service identifier. */
{
    {BLE_UUID_NUS_SERVICE, NUS_SERVICE_UUID_TYPE}
};
static char m_nus_data_array[BLE_NUS_MAX_DATA_LEN];

// BLE DEFINES END

/**
 * @brief Function for assert macro callback.
 *
 * @details This function will be called in case of an assert in the SoftDevice.
 *
 * @warning This handler is an example only and does not fit a final product. You need to analyze
 *          how your product is supposed to react in case of an assert.
 * @warning On assert from the SoftDevice, the system can only recover on reset.
 *
 * @param[in] line_num    Line number of the failing ASSERT call.
 * @param[in] p_file_name File name of the failing ASSERT call.
 */
void assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name)
{
    app_error_handler(DEAD_BEEF, line_num, p_file_name);
}

/** @brief Function for initializing the timer module. */
static void timers_init(void)
{
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
    err_code = app_timer_create(&m_blink_ble, APP_TIMER_MODE_REPEATED, blink_handler);
    APP_ERROR_CHECK(err_code);
    err_code = app_timer_create(&m_blink_cdc, APP_TIMER_MODE_REPEATED, blink_handler);
    APP_ERROR_CHECK(err_code);
    err_code = app_timer_create(&m_system_off, APP_TIMER_MODE_SINGLE_SHOT, system_off_trigger);
    APP_ERROR_CHECK(err_code);
}

/**
 * @brief Function for the GAP initialization.
 *
 * @details This function sets up all the necessary GAP (Generic Access Profile) parameters of
 *          the device. It also sets the permissions and appearance.
 */
static void gap_params_init(void)
{
    uint32_t                err_code;
    ble_gap_conn_params_t   gap_conn_params;
    ble_gap_conn_sec_mode_t sec_mode;

    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&sec_mode);

    err_code = sd_ble_gap_device_name_set(&sec_mode,
                                          (const uint8_t *) DEVICE_NAME,
                                          strlen(DEVICE_NAME));
    APP_ERROR_CHECK(err_code);

    memset(&gap_conn_params, 0, sizeof(gap_conn_params));

    gap_conn_params.min_conn_interval = MIN_CONN_INTERVAL;
    gap_conn_params.max_conn_interval = MAX_CONN_INTERVAL;
    gap_conn_params.slave_latency     = SLAVE_LATENCY;
    gap_conn_params.conn_sup_timeout  = CONN_SUP_TIMEOUT;

    err_code = sd_ble_gap_ppcp_set(&gap_conn_params);
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for handling the data from the Nordic UART Service.
 *
 * @details This function processes the data received from the Nordic UART BLE Service and sends
 *          it to the USBD CDC ACM module.
 *
 * @param[in] p_evt Nordic UART Service event.
 */
static void nus_data_handler(ble_nus_evt_t * p_evt)
{

    if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
        bsp_board_led_invert(LED_BLE_NUS_RX);
        NRF_LOG_DEBUG("Received data from BLE NUS. Writing data on CDC ACM.");
        NRF_LOG_HEXDUMP_DEBUG(p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);
        memcpy(m_nus_data_array, p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);

        // Add endline characters
        uint16_t length = p_evt->params.rx_data.length;
        if (length + sizeof(ENDLINE_STRING) < BLE_NUS_MAX_DATA_LEN)
        {
            memcpy(m_nus_data_array + length, ENDLINE_STRING, sizeof(ENDLINE_STRING));
            length += sizeof(ENDLINE_STRING);
        }

        // Send data through CDC ACM
        ret_code_t ret = app_usbd_cdc_acm_write(&m_app_cdc_acm,
                                                m_nus_data_array,
                                                length);
        if(ret != NRF_SUCCESS)
        {
            NRF_LOG_INFO("CDC ACM unavailable, data received: %s", m_nus_data_array);
        }
    }

}


/** @brief Function for initializing services that will be used by the application. */
static void services_init(void)
{
    uint32_t       err_code;
    ble_nus_init_t nus_init;

    memset(&nus_init, 0, sizeof(nus_init));

    nus_init.data_handler = nus_data_handler;

    err_code = ble_nus_init(&m_nus, &nus_init);
    APP_ERROR_CHECK(err_code);
}

/**
 * @brief Function for handling errors from the Connection Parameters module.
 *
 * @param[in] nrf_error  Error code containing information about what went wrong.
 */
static void conn_params_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}


/** @brief Function for initializing the Connection Parameters module. */
static void conn_params_init(void)
{
    uint32_t               err_code;
    ble_conn_params_init_t cp_init;

    memset(&cp_init, 0, sizeof(cp_init));

    cp_init.p_conn_params                  = NULL;
    cp_init.first_conn_params_update_delay = FIRST_CONN_PARAMS_UPDATE_DELAY;
    cp_init.next_conn_params_update_delay  = NEXT_CONN_PARAMS_UPDATE_DELAY;
    cp_init.max_conn_params_update_count   = MAX_CONN_PARAMS_UPDATE_COUNT;
    cp_init.start_on_notify_cccd_handle    = BLE_GATT_HANDLE_INVALID;
    cp_init.disconnect_on_fail             = true;
    cp_init.evt_handler                    = NULL;
    cp_init.error_handler                  = conn_params_error_handler;

    err_code = ble_conn_params_init(&cp_init);
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for putting the chip into sleep mode.
 *
 * @note This function does not return.
 */
static void sleep_mode_enter(void)
{
    uint32_t err_code = bsp_indication_set(BSP_INDICATE_IDLE);
    APP_ERROR_CHECK(err_code);

    // Prepare wakeup buttons.
    err_code = bsp_btn_ble_sleep_mode_prepare();
    APP_ERROR_CHECK(err_code);

    // Go to system-off mode (this function will not return; wakeup will cause a reset).
    err_code = sd_power_system_off();
    APP_ERROR_CHECK(err_code);
}


/** @brief Function for starting advertising. */
static void advertising_start(void)
{
    uint32_t err_code = ble_advertising_start(&m_advertising, BLE_ADV_MODE_FAST);
    APP_ERROR_CHECK(err_code);
}

/**
 * @brief Function for handling advertising events.
 *
 * @details This function is called for advertising events which are passed to the application.
 *
 * @param[in] ble_adv_evt  Advertising event.
 */
static void on_adv_evt(ble_adv_evt_t ble_adv_evt)
{
    uint32_t err_code;

    switch (ble_adv_evt)
    {
        case BLE_ADV_EVT_FAST:
            err_code = app_timer_start(m_blink_ble,
                                       APP_TIMER_TICKS(LED_BLINK_INTERVAL),
                                       (void *) LED_BLE_NUS_CONN);
            APP_ERROR_CHECK(err_code);
            break;
        case BLE_ADV_EVT_IDLE:
            NRF_LOG_INFO("Advertising timeout, restarting.")
            advertising_start();
            break;
        default:
            break;
    }
}


/**
 * @brief Function for handling BLE events.
 *
 * @param[in]   p_ble_evt   Bluetooth stack event.
 * @param[in]   p_context   Unused.
 */
static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context)
{
    uint32_t err_code;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GAP_EVT_CONNECTED:
            NRF_LOG_INFO("BLE NUS connected");
            err_code = app_timer_stop(m_blink_ble);
            APP_ERROR_CHECK(err_code);
            bsp_board_led_on(LED_BLE_NUS_CONN);
            m_conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
            break;

        case BLE_GAP_EVT_DISCONNECTED:
            NRF_LOG_INFO("BLE NUS disconnected");
            // LED indication will be changed when advertising starts.
            m_conn_handle = BLE_CONN_HANDLE_INVALID;
            break;

        case BLE_GAP_EVT_PHY_UPDATE_REQUEST:
        {
            NRF_LOG_DEBUG("PHY update request.");
            ble_gap_phys_t const phys =
            {
                .rx_phys = BLE_GAP_PHY_AUTO,
                .tx_phys = BLE_GAP_PHY_AUTO,
            };
            err_code = sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);
            APP_ERROR_CHECK(err_code);
        } break;

        case BLE_GAP_EVT_SEC_PARAMS_REQUEST:
            // Pairing not supported.
            err_code = sd_ble_gap_sec_params_reply(m_conn_handle, BLE_GAP_SEC_STATUS_PAIRING_NOT_SUPP, NULL, NULL);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST:
        {
            ble_gap_data_length_params_t dl_params;

            // Clearing the struct will effectively set members to @ref BLE_GAP_DATA_LENGTH_AUTO.
            memset(&dl_params, 0, sizeof(ble_gap_data_length_params_t));
            err_code = sd_ble_gap_data_length_update(p_ble_evt->evt.gap_evt.conn_handle, &dl_params, NULL);
            APP_ERROR_CHECK(err_code);
        } break;

        case BLE_GATTS_EVT_SYS_ATTR_MISSING:
            // No system attributes have been stored.
            err_code = sd_ble_gatts_sys_attr_set(m_conn_handle, NULL, 0, 0);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTC_EVT_TIMEOUT:
            // Disconnect on GATT Client timeout event.
            err_code = sd_ble_gap_disconnect(p_ble_evt->evt.gattc_evt.conn_handle,
                                             BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTS_EVT_TIMEOUT:
            // Disconnect on GATT Server timeout event.
            err_code = sd_ble_gap_disconnect(p_ble_evt->evt.gatts_evt.conn_handle,
                                             BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_EVT_USER_MEM_REQUEST:
            err_code = sd_ble_user_mem_reply(p_ble_evt->evt.gattc_evt.conn_handle, NULL);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST:
        {
            ble_gatts_evt_rw_authorize_request_t  req;
            ble_gatts_rw_authorize_reply_params_t auth_reply;

            req = p_ble_evt->evt.gatts_evt.params.authorize_request;

            if (req.type != BLE_GATTS_AUTHORIZE_TYPE_INVALID)
            {
                if ((req.request.write.op == BLE_GATTS_OP_PREP_WRITE_REQ)     ||
                    (req.request.write.op == BLE_GATTS_OP_EXEC_WRITE_REQ_NOW) ||
                    (req.request.write.op == BLE_GATTS_OP_EXEC_WRITE_REQ_CANCEL))
                {
                    if (req.type == BLE_GATTS_AUTHORIZE_TYPE_WRITE)
                    {
                        auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_WRITE;
                    }
                    else
                    {
                        auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_READ;
                    }
                    auth_reply.params.write.gatt_status = APP_FEATURE_NOT_SUPPORTED;
                    err_code = sd_ble_gatts_rw_authorize_reply(p_ble_evt->evt.gatts_evt.conn_handle,
                                                               &auth_reply);
                    APP_ERROR_CHECK(err_code);
                }
            }
        } break; // BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST

        default:
            // No implementation needed.
            break;
    }
}


/**
 * @brief Function for the SoftDevice initialization.
 *
 * @details This function initializes the SoftDevice and the BLE event interrupt.
 */
static void ble_stack_init(void)
{
    ret_code_t err_code;

    err_code = nrf_sdh_enable_request();
    APP_ERROR_CHECK(err_code);

    // Configure the BLE stack using the default settings.
    // Fetch the start address of the application RAM.
    uint32_t ram_start = 0;
    err_code = nrf_sdh_ble_default_cfg_set(APP_BLE_CONN_CFG_TAG, &ram_start);
    APP_ERROR_CHECK(err_code);

    // Enable BLE stack.
    err_code = nrf_sdh_ble_enable(&ram_start);
    APP_ERROR_CHECK(err_code);

    // Register a handler for BLE events.
    NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL);
}


/** @brief Function for handling events from the GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
    if ((m_conn_handle == p_evt->conn_handle) && (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED))
    {
        m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;
        NRF_LOG_INFO("Data len is set to 0x%X(%d)", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
    }
    NRF_LOG_DEBUG("ATT MTU exchange completed. central 0x%x peripheral 0x%x",
                  p_gatt->att_mtu_desired_central,
                  p_gatt->att_mtu_desired_periph);
}


/** @brief Function for initializing the GATT library. */
void gatt_init(void)
{
    ret_code_t err_code;

    err_code = nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 64);
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for handling events from the BSP module.
 *
 * @param[in]   event   Event generated by button press.
 */
void bsp_event_handler(bsp_event_t event)
{
    uint32_t err_code;
    switch (event)
    {
        case BSP_EVENT_SLEEP:
            sleep_mode_enter();
            break;

        case BSP_EVENT_DISCONNECT:
            err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            if (err_code != NRF_ERROR_INVALID_STATE)
            {
                APP_ERROR_CHECK(err_code);
            }
            break;

        case BSP_EVENT_WHITELIST_OFF:
            if (m_conn_handle == BLE_CONN_HANDLE_INVALID)
            {
                err_code = ble_advertising_restart_without_whitelist(&m_advertising);
                if (err_code != NRF_ERROR_INVALID_STATE)
                {
                    APP_ERROR_CHECK(err_code);
                }
            }
            break;

        default:
            break;
    }
}

/** @brief Function for initializing the Advertising functionality. */
static void advertising_init(void)
{
    uint32_t               err_code;
    ble_advertising_init_t init;

    memset(&init, 0, sizeof(init));

    init.advdata.name_type          = BLE_ADVDATA_FULL_NAME;
    init.advdata.include_appearance = false;
    init.advdata.flags              = BLE_GAP_ADV_FLAGS_LE_ONLY_LIMITED_DISC_MODE;

    init.srdata.uuids_complete.uuid_cnt = sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
    init.srdata.uuids_complete.p_uuids  = m_adv_uuids;

    init.config.ble_adv_fast_enabled  = true;
    init.config.ble_adv_fast_interval = APP_ADV_INTERVAL;
    init.config.ble_adv_fast_timeout  = APP_ADV_DURATION;

    init.evt_handler = on_adv_evt;

    err_code = ble_advertising_init(&m_advertising, &init);
    APP_ERROR_CHECK(err_code);

    ble_advertising_conn_cfg_tag_set(&m_advertising, APP_BLE_CONN_CFG_TAG);
}


/** @brief Function for initializing buttons and LEDs. */
static void buttons_leds_init(void)
{
    uint32_t err_code = bsp_init(BSP_INIT_LEDS, bsp_event_handler);
    APP_ERROR_CHECK(err_code);
}


/** @brief Function for initializing the nrf_log module. */
static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


/** @brief Function for placing the application in low power state while waiting for events. */
static void power_manage(void)
{
    uint32_t err_code = sd_app_evt_wait();
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for handling the idle state (main loop).
 *
 * @details If there is no pending log operation, then sleep until next the next event occurs.
 */
static void idle_state_handle(void)
{
    UNUSED_RETURN_VALUE(NRF_LOG_PROCESS());
    power_manage();
}


// USB CODE START
static bool m_usb_connected = false;


/** @brief User event handler @ref app_usbd_cdc_acm_user_ev_handler_t */
static void cdc_acm_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                    app_usbd_cdc_acm_user_event_t event)
{
    app_usbd_cdc_acm_t const * p_cdc_acm = app_usbd_cdc_acm_class_get(p_inst);

    switch (event)
    {
        case APP_USBD_CDC_ACM_USER_EVT_PORT_OPEN:
        {
            /*Set up the first transfer*/
            ret_code_t ret = app_usbd_cdc_acm_read(&m_app_cdc_acm,
                                                   m_cdc_data_array,
                                                   1);
            UNUSED_VARIABLE(ret);
            ret = app_timer_stop(m_blink_cdc);
            APP_ERROR_CHECK(ret);
            bsp_board_led_on(LED_CDC_ACM_CONN);
            NRF_LOG_INFO("CDC ACM port opened");
            break;
        }

        case APP_USBD_CDC_ACM_USER_EVT_PORT_CLOSE:
            NRF_LOG_INFO("CDC ACM port closed");
            if (m_usb_connected)
            {
                ret_code_t ret = app_timer_start(m_blink_cdc,
                                                 APP_TIMER_TICKS(LED_BLINK_INTERVAL),
                                                 (void *) LED_CDC_ACM_CONN);
                APP_ERROR_CHECK(ret);
            }
            break;

        case APP_USBD_CDC_ACM_USER_EVT_TX_DONE:
            break;

        case APP_USBD_CDC_ACM_USER_EVT_RX_DONE:
        {
            ret_code_t ret;
            static uint8_t index = 0;
            index++;

            do
            {
                if ((m_cdc_data_array[index - 1] == '\n') ||
                    (m_cdc_data_array[index - 1] == '\r') ||
                    (index >= (m_ble_nus_max_data_len)))
                {
                    if (index > 1)
                    {
                        bsp_board_led_invert(LED_CDC_ACM_RX);
                        NRF_LOG_DEBUG("Ready to send data over BLE NUS");
                        NRF_LOG_HEXDUMP_DEBUG(m_cdc_data_array, index);

                        do
                        {
                            uint16_t length = (uint16_t)index;
                            if (length + sizeof(ENDLINE_STRING) < BLE_NUS_MAX_DATA_LEN)
                            {
                                memcpy(m_cdc_data_array + length, ENDLINE_STRING, sizeof(ENDLINE_STRING));
                                length += sizeof(ENDLINE_STRING);
                            }

                            ret = ble_nus_data_send(&m_nus,
                                                    (uint8_t *) m_cdc_data_array,
                                                    &length,
                                                    m_conn_handle);

                            if (ret == NRF_ERROR_NOT_FOUND)
                            {
                                NRF_LOG_INFO("BLE NUS unavailable, data received: %s", m_cdc_data_array);
                                break;
                            }

                            if (ret == NRF_ERROR_RESOURCES)
                            {
                                NRF_LOG_ERROR("BLE NUS Too many notifications queued.");
                                break;
                            }

                            if ((ret != NRF_ERROR_INVALID_STATE) && (ret != NRF_ERROR_BUSY))
                            {
                                APP_ERROR_CHECK(ret);
                            }
                        }
                        while (ret == NRF_ERROR_BUSY);
                    }

                    index = 0;
                }

                /*Get amount of data transferred*/
                size_t size = app_usbd_cdc_acm_rx_size(p_cdc_acm);
                NRF_LOG_DEBUG("RX: size: %lu char: %c", size, m_cdc_data_array[index - 1]);

                /* Fetch data until internal buffer is empty */
                ret = app_usbd_cdc_acm_read(&m_app_cdc_acm,
                                            &m_cdc_data_array[index],
                                            1);
                if (ret == NRF_SUCCESS)
                {
                    index++;
                }
            }
            while (ret == NRF_SUCCESS);

            break;
        }
        default:
            break;
    }
}

static void usbd_user_ev_handler(app_usbd_event_type_t event)
{
    switch (event)
    {
        case APP_USBD_EVT_DRV_SUSPEND:
            break;

        case APP_USBD_EVT_DRV_RESUME:
            break;

        case APP_USBD_EVT_STARTED:
            break;

        case APP_USBD_EVT_STOPPED:
            app_usbd_disable();
            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");
            ret_code_t err_code = app_timer_stop(m_blink_cdc);
            APP_ERROR_CHECK(err_code);
            bsp_board_led_off(LED_CDC_ACM_CONN);
            m_usb_connected = false;
            app_usbd_stop();
        }
            break;

        case APP_USBD_EVT_POWER_READY:
        {
            NRF_LOG_INFO("USB ready");
            ret_code_t err_code = app_timer_start(m_blink_cdc,
                                                  APP_TIMER_TICKS(LED_BLINK_INTERVAL),
                                                  (void *) LED_CDC_ACM_CONN);
            APP_ERROR_CHECK(err_code);
            m_usb_connected = true;
            app_usbd_start();
        }
            break;

        default:
            break;
    }
}

// USB CODE END

/** @brief Application main function. */
int main(void)
{
    ret_code_t ret;
    static const app_usbd_config_t usbd_config = {
        .ev_state_proc = usbd_user_ev_handler
    };
    // Initialize.
    log_init();
    timers_init();

    buttons_leds_init();

    app_usbd_serial_num_generate();

    ret = nrf_drv_clock_init();
    APP_ERROR_CHECK(ret);

    NRF_LOG_INFO("USBD BLE UART example started.");

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

    app_usbd_class_inst_t const * class_cdc_acm = app_usbd_cdc_acm_class_inst_get(&m_app_cdc_acm);
    ret = app_usbd_class_append(class_cdc_acm);
    APP_ERROR_CHECK(ret);

    ble_stack_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    conn_params_init();

    // Start execution.
    advertising_start();

    ret = app_usbd_power_events_enable();
    APP_ERROR_CHECK(ret);

    ret = app_timer_start(m_system_off,
                          APP_TIMER_TICKS(5000),
                          NULL);
    APP_ERROR_CHECK(ret);



    // Enter main loop.
    for (;;)
    {
        while (app_usbd_event_queue_process())
        {
            /* Nothing to do */
        }
        idle_state_handle();
    }
}

/**
 * @}
 */

[GPL]

Hello again Sigurd,

I managed to solve the issue. Looking at your example I noticed that you wait to enable the power events up until the last moment before your main loop. In my code I enabled those events before I did the (quite hefty) BLE related initializations, if I call `app_usbd_power_events_enable()` just before the main loop and after the BLE initializations, everything is working as expected.

Thank you for your time