Sending 32 bit of data over BLE onto nrf52832

[swathi p]

Hi,

I have used "write_handler(p_ble_evt->evt.gap_evt.conn_handle, p_rtc_service, p_evt_write->data[0]);" to send data to nrf52832 from mobile but iam able to send  1 byte data as it is meant to be predefined in the gatts structure i.e

/**@brief Event structure for @ref BLE_GATTS_EVT_WRITE. */
typedef struct
{
uint16_t handle;                  /**< Attribute Handle. */
ble_uuid_t uuid;                  /**< Attribute UUID. */
uint8_t op;                       /**< Type of write operation, see @ref BLE_GATTS_OPS. */
uint8_t auth_required;            /**< Writing operation deferred due to authorization requirement. Application may use @ref sd_ble_gatts_value_set to finalize the writing operation. */
uint16_t offset;                   /**< Offset for the write operation. */
uint16_t len;                      /**< Length of the received data. */
uint8_t data[1];                   /**< Received data. @note This is a variable length array. The size of 1 indicated is only a placeholder for compilation.
See @ref sd_ble_evt_get for more information on how to use event structures with variable length array members. */
uint32_t data1[1];
} ble_gatts_evt_write_t;

If i want to send 32 bit data can i try making change to uint8_t data[0] as uint32_t data[0]??If this is not the right way please let me know with what changes will i be able to send 32 bit data to nrf52832 from mobile?

Thank you.

[BinderT]

Hi,

Just no,

Split your 32 bit data into an array of uint8_t(s) and and set that array equal to ble_gatts_evt_write_t ->data. ble_gatts_evt_write_t ->len should be set as the length of data sent in bytes.

example code

ble_gatts_evt_write_t params;

uint32_t data = 0x12345678

uint8_t buffer[sizeof(uint32_t)];


void set_data(uint32_t *data, uint8_t *buffer,uint16_t len){
    memcpy(buffer,data,len);
}


void main(void){
    set_data(&data,buffer,sizeof(buffer));
    // buffer = {78,56,34,12}
    
    params.data = data;
    params.len = sizeof(uint32_t)
    
}

data[1] is a pointer to the start of an array of uint8_t(s).

Example of sending more than one byte of data as a notification.

uint32_t ble_packet_send(
		ble_service_t * p_service, // service handle
		packet_u * p_packet){ // data to send

		uint32_t err_code = NRF_SUCCESS;

		if (p_service->conn_handle != BLE_CONN_HANDLE_INVALID) {
			ble_gatts_hvx_params_t hvx_params;
			uint8_t encoded_value[sizeof(packet_u)]; // array to split data
			uint16_t hvx_len;

			// Initialize value struct.
			memset(&hvx_params, 0, sizeof(hvx_params));

			hvx_len = ble_encode(p_respons_packet, encoded_value); // lenght in bytes 
			hvx_params.handle =p_service->ble_handles.value_handle;
			hvx_params.type = BLE_GATT_HVX_NOTIFICATION;
			hvx_params.p_len = &hvx_len;
			hvx_params.offset = 0;
			hvx_params.p_data = encoded_value; //split data to send

			err_code = sd_ble_gatts_hvx(p_service->conn_handle,&hvx_params);
		} else {
			err_code = NRF_ERROR_INVALID_STATE;
		}

		return err_code;
}

You should also set ble_add_char_params_t.max_len to the size of the data in bytes you intend to send in you service init.

Regards