No return value for sd_ble_gatts_hvx()

[Yacire]

Hi All,

I have a problem with the function sd_ble_gatts_hvx(). I have no return value when i call this function and i don't understand why ?

I have a function where i update a battery level value (uint8_t) and i notify the central, like this :

static void battery_level_handler(void *p_context) {

ble_lbs_t* p_m_lbs = &m_lbs;

if (p_m_lbs->conn_handle != BLE_CONN_HANDLE_INVALID) {
		
ble_gatts_hvx_params_t hvx_params;
uint32_t err_code;
uint16_t len = 1;
	
memset(&hvx_params, 0, sizeof(hvx_params));

    hvx_params.handle = p_m_lbs->battery_char_handles.value_handle;
    hvx_params.p_data = &initialValueBattery;
hvx_params.offset = 0;
    hvx_params.p_len  = &len;
    hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;

    err_code = sd_ble_gatts_hvx(p_m_lbs->conn_handle, &hvx_params);
// SEGGER_RTT_printf(CHANNEL_RTT, "err_code: %d\n", err_code);
APP_ERROR_CHECK(err_code);

	if(initialValueBattery <= 20) initialValueBattery = 100;

	initialValueBattery = initialValueBattery - 1;
	
	}

}

And i add the battery characteristic to the service like this :

static uint32_t battery_charac_add(ble_lbs_t * p_lbs, const ble_lbs_init_t * p_lbs_init) {

ble_gatts_char_md_t char_md;
ble_gatts_attr_md_t cccd_md;
ble_gatts_attr_t    attr_char_value;
ble_uuid_t          ble_uuid;
ble_gatts_attr_md_t attr_md;

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

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&cccd_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_OPEN(&cccd_md.write_perm);

cccd_md.vloc = BLE_GATTS_VLOC_STACK;

memset(&char_md, 0, sizeof(char_md));
// char_md.char_props.read   = 1;
char_md.char_props.notify   = 1;
char_md.p_char_user_desc  = NULL;
char_md.p_char_pf         = NULL;
char_md.p_user_desc_md    = NULL;
char_md.p_cccd_md         = &cccd_md;
char_md.p_sccd_md         = NULL;

ble_uuid.type = p_lbs->uuid_type;
ble_uuid.uuid = UUID_BATTERY_CHAR;

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

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);
attr_md.vloc       = BLE_GATTS_VLOC_STACK;
attr_md.rd_auth    = 0;
attr_md.wr_auth    = 0;
attr_md.vlen       = 0;

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

attr_char_value.p_uuid       = &ble_uuid;
attr_char_value.p_attr_md    = &attr_md;
attr_char_value.init_len     = sizeof(uint8_t);
attr_char_value.init_offs    = 0;
attr_char_value.max_len      = sizeof(uint8_t);
attr_char_value.p_value      = (uint8_t*) &initialValueBattery;

return sd_ble_gatts_characteristic_add(p_lbs->service_handle,
                                       &char_md,
                                       &attr_char_value,
                                       &p_lbs->battery_char_handles);

}

But i don't understand when i upload the code, the nRF51 reset when he reaches the line :

err_code = sd_ble_gatts_hvx(p_m_lbs->conn_handle, &hvx_params);

And the function sd_ble_gatts_hvx return no value.

I work with the SDK10 and S110 v8.0.0 (nrf51422 SOC).

Thanks for your help.

[Petter Myhre]

I tested your project, I just commented in app_timer_start(battery_level_timer, APP_TIMER_TICKS(time_measure_adc, APP_TIMER_PRESCALER), NULL); and turned off optimizations.

I put a breakpoint on APP_ERROR_CHECK(err_code); and I got error code 0x3401, which is BLE_ERROR_GATTS_SYS_ATTR_MISSING. See this for how to fix it.

I modified your code with:

    err_code = sd_ble_gatts_hvx(p_m_lbs->conn_handle, &hvx_params);
    SEGGER_RTT_printf(CHANNEL_RTT, "err_code: %d\n", err_code);
        
    if(err_code == BLE_ERROR_GATTS_SYS_ATTR_MISSING)
    {
        err_code = sd_ble_gatts_sys_attr_set(m_conn_handle, NULL, 0, 0);
        APP_ERROR_CHECK(err_code);
    }
    else
    {
        APP_ERROR_CHECK(err_code);
    }

And put a breakpoint on APP_ERROR_CHECK(err_code); in the else, and then I got error code 0x0008, which is NRF_ERROR_INVALID_STATE. This is because notifications are not enabled, because the CCCD hasn't been set by the client.

If you are not experiencing the same, please let me know.

[Yacire]

Thanks a lot Petter, first i want to thank the Nordic's Support Team, your help is really great !

Ok , now the problem:

I have the same error code BLE_ERROR_GATTS_SYS_ATTR_MISSING, so i added the two lines in the if(...){}.But now the nrf51 reset in the else{}, there is no more freeze of the nrf51.

So, I have a question about the CCCD, how i can set the CCCD by the client before the nrf51 reset ?

In the else {} the nrf51 reset because i don't have the time to set the CCCD with nrfConnect (click on "enable services"), when i change the time of the timer it works because i have the time to click on "enable services" in the nrfConnect application.

[Petter Myhre]

You have two options, either not call sd_ble_gatts_hvx() before the CCCD is actually set, or handle the error returned from sd_ble_gatts_hvx(), i.e. not call APP_ERROR_CHECK() with it.

[Yacire]

Hi Petter,

I tested without check err_code (APP_ERROR_CHECK) and it works. But i want to know if CCCD is set and then call sd_ble_gatts_hvx().

So in this post : link text , i see Ole Morten advise to read the value of the CCCD using sd_ble_gatts_value_get(), and check whether it is 0x0001 (Notification) or 0x0002 (Indication), but i don't understand how i can check the value of CCCD using this function ??

[Petter Myhre]

I don't recommend removing the APP_ERROR_CHECK completely, but ok. Ole Morten doesn't advise that. He says it is possible, his advice is to use method 1 or 2. If you don't undestand how to use sd_ble_gatts_value_get() you should add a new question and explain how you are using it, and what you don't understand.

[Yacire]

Thanks for the answer,

I didn't removed completely the APP_ERROR_CHECK macro, just in the else {} when the err_code variable is equal to NRF_ERROR_INVALID_STATE ( i removed the else{} ).

Ok, i will open a new post, because the use of sd_ble_gatts_value_get() for reading the CCCD value isn't clear for me.