I want to solve the problem that the characteristic value is not the set value.

[sdi_kei]

Hello.

It is being developed using nrf52832 (S132 v7.0.1, SDK v17.0.0) as a peripheral device.

Previously, I inquired about how to add a value to the characteristic with this ticket, the error no longer occurs, I can connect, I can confirm that the value of the characteristic is set, and it is solved safely I was able to do it.

However, although no error now occurs, the characteristic value is no longer the set value.

I don't know why this is happening. Do you have any advice?

Also, I am currently inquiring with this ticket, but I am creating a process to switch the advertised UUID. Isn't this advertisement UUID and service UUID need to be linked? I searched for such a process, but couldn't find it.

Best regards.

[Einar Thorsrud]

Hi,

However, although no error now occurs, the characteristic value is no longer the set value.

I don't know why this is happening. Do you have any advice?

What have you changed since it did work? What value do you write and what do you see? Could it be that other parts of your code sets another value, or that you do not set it at all? If you explain and show your code I can take a look and see if I spot any issues.

Also, I am currently inquiring with this ticket, but I am creating a process to switch the advertised UUID. Isn't this advertisement UUID and service UUID need to be linked? I searched for such a process, but couldn't find it.

If you advertise a service UUID, then that indicates that your device supports that service. There is however no direct link, so you can technically advertise any UUID(s) regardless of what services the peripheral actually implements. For instance if you take a look at examples\ble_peripheral\ble_app_hrs\main.c you can see some UUIDs that are part of the advertisement packet by looking at how m_adv_uuids is declared. Implementation-vise this is completely independent of adding the services themselves. 

[sdi_kei]

Hello.

Since the actual code cannot be published, some contents are different, but we are considering such code.

// UUID Setting
#define ADV_UUID_BASE     {0x77, 0x77, 0x66, 0x66, 0x55, 0x55, 0x44, 0x44, 0x33, 0x33, 0x22, 0x22, 0x11, 0x11, 0x00, 0x00}
#define SERVICE_UUID_BASE {0x0F, 0x0E, 0x0D, 0x0C, 0x0B, 0x0A, 0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00}
#define CHAR_UUID_BASE    {0xF0, 0xE0, 0xD0, 0xC0, 0xB0, 0xA0, 0x90, 0x80, 0x70, 0x60, 0x50, 0x40, 0x30, 0x20, 0x10, 0x00}
#define BLE_UUID_CHAR     {0x1234}

#define BLE_UUID_CHAR_MAX {1}

// Connection Handle
static uint16_t                 m_service_handle;   /**< Handle of local service (as provided by the BLE stack).*/
static ble_gatts_char_handles_t m_char_handles;     /**< Handles of local characteristic (as provided by the BLE stack).*/
static uint16_t                 conn_handle;

// Characteristic
static ble_add_char_params_t char_test_data = 
{
    .uuid                = BLE_UUID_CHAR,
    .uuid_type           = NULL,
    .max_len             = 1,
    .init_len            = 1,
    .is_var_len          = false,
    .char_props.read     = 1,
    .read_access         = SEC_MITM,
    .is_value_user       = BLE_GATTS_VLOC_STACK,
};

// UUID Base
static ble_uuid128_t ble_char_uuid_base[BLE_UUID_CHAR_MAX] = 
{
    CHAR1_UUID_BASE,
};

// set the UUID here.
static void uuid_init(void)
{
    ret_code_t    err_code;
    ble_uuid_t    adv_uuid;
    ble_uuid_t    service_uuid;
    ble_uuid_t    char_uuid;
    ble_uuid128_t adv_uuid_base = {ADV_UUID_BASE};
    ble_uuid128_t service_uuid_base = {SERVICE_UUID_BASE};

    uint8_t       test_data = 0x01;

    // advertise setting
    err_code = sd_ble_uuid_vs_add(&adv_uuid_base, &adv_uuid.type);
    APP_ERROR_CHECK(err_code);

    // service setting
    err_code = sd_ble_uuid_vs_add(&service_uuid_base, &service_uuid.type);
    APP_ERROR_CHECK(err_code);

    err_code = sd_ble_gatts_service_add(BLE_GATTS_SRVC_TYPE_PRIMARY, &service_uuid, &m_service_handle);
    APP_ERROR_CHECK(err_code);

    // characteristic setting
    err_code = sd_ble_uuid_vs_add(&ble_char_uuid_base[0], &char_uuid.type);
    APP_ERROR_CHECK(err_code);

    add_char_params.uuid_type = char_uuid.type;
    err_code = characteristic_add(m_service_handle, &add_char_params, &m_char_handles);
    APP_ERROR_CHECK(err_code);

    char_data_set(m_char_handles, 1, &test_data);

    return;
}

// characteristic data setting.
static void char_data_set(uint16_t handle, uint8_t len, uint8_t * value)
{
    ret_code_t        err_code;
    ble_gatts_value_t char_value;

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

    char_value.len     = len;
    char_value.offset  = 0;
    char_value.p_value = value;

    err_code = sd_ble_gatts_value_set(BLE_CONN_HANDLE_INVALID, handle, &char_value);
    APP_ERROR_CHECK(err_code);

    return;
}

Since the characteristic is set to read, it is assumed that a Read Request will be received from the connected BLE device (nRF Connect) and the data will be acquired.

In this code, it is 1Byte, but when I set the data of about 8Byte and acquired it with a BLE device, it was the same value as the address 0x00000000 in the memory. Why is the data at address 0x00000000 sent?

[Einar Thorsrud]

You do not get an even in the nRF indicating that the read response has been sent. But it will be, and if it is not being delivered for some reason, then after several attempted retransmissions, the link will be disconnected with timeout as disconnect reason. As long as this does not happen, the data has been exchanged.

[sdi_kei]

Hello.

I have confirmed that the response is returned when connecting with nRF Connect. However, the values are different.

I haven't had time to create a minimal example.
Is there an example in the SDK?

Best regards.

[Einar Thorsrud]

Most of the BLE peripheral examples in the SDK includes a characteristic that is written to that you can read (though most also notify it, so you may want to disable notification if you pick for instance the Heart Rate Application example). 

[sdi_kei]

Hello.

As a result of repeated investigations, we were able to solve the problem.

The cause is that the setting of "is_value_user" was wrong as described in the code example. Previously, I wasn't using "is_value_user", so it worked fine.

The code said ".is_value_user = BLE_GATTS_VLOC_STACK", but ".is_value_user = false" was correct. Now that I've corrected the code, I can read the settings.

Best regards.

[Einar Thorsrud]

Hi,

Good to hear you solved the issue. I did not spot that, but it makes full sense. Thank you for letting us know!