writing to a ble characteristic

RE: writing to a ble characteristic

ropz — Mon, 03 Jun 2024 22:24:12 GMT

Hi Youssef, do you know how to obtain the handle value of the attribute or the RX or TX characteristics. Is it initialized with how you defined your sevice or it is related to the UUID? For right now I am kind of stucking in obtaining the handle value of the RX characteristic which I want to write into.

RE: writing to a ble characteristic

Youssef Elbattah — Tue, 28 May 2024 11:42:46 GMT

characteristic_handle is same as characteristic_handle_date because i have changed its name, now i have incremented its value by 1 and it works, thank you so much for your help.

But can you please explain to me why when the value is incremented the write operation works ?

RE: writing to a ble characteristic

Vidar Berg — Mon, 27 May 2024 12:34:35 GMT

The code snippets do not show where the 'characteristic_handle' is assigned. Do you see the same if you increment 'characteristic_handle' by 1? Maybe the handle is pointing to the characteristic containing the UUID, and not the value handle for the characteristic.

RE: writing to a ble characteristic

Youssef Elbattah — Fri, 24 May 2024 14:15:50 GMT

and this is the declaration of my service characteristic :

BT_GATT_CHARACTERISTIC(BT_UUID_LBS_DATE, BT_GATT_CHRC_WRITE, BT_GATT_PERM_WRITE, NULL,
                   write_date, NULL),

RE: writing to a ble characteristic

Youssef Elbattah — Fri, 24 May 2024 14:14:34 GMT

Yes i think that i'm writing to the correcte handler because the characteristic that i want to modify is BT_UUID_LBS_DATE and i store it's handler value here :

else if (!bt_uuid_cmp(discover_params.uuid,
                BT_UUID_LBS_DATE)) {

        //write_characteristic(default_conn)
        characteristic_handle_date = attr->handle;
        printk("MYSENSOR characteristic discovered\n");
        memcpy(&discover_uuid, BT_UUID_LBS_MYSENSOR, sizeof(discover_uuid));
        discover_params.uuid = &discover_uuid.uuid;
        discover_params.start_handle = attr->handle - 3;
        discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
        err = bt_gatt_discover(conn, &discover_params);
        if (err) {
            printk("Discover failed (err %d)\n", err);
        }
        //return BT_GATT_ITER_STOP;
    }

RE: writing to a ble characteristic

Vidar Berg — Fri, 24 May 2024 14:11:27 GMT

Error 3 is BT_ATT_ERR_WRITE_NOT_PERMITTED, so you may want to double check that you are writing to the correct attribute handle.

RE: writing to a ble characteristic

Youssef Elbattah — Fri, 24 May 2024 13:48:36 GMT

yes it works but the function 'write func' returns : Write failed: 3

static void write_func(struct bt_conn *conn, uint8_t err,
                       struct bt_gatt_write_params *params)
{
    if (err) {
        printk("Write failed: %u\n", err);
    } else {
        printk("Write successful\n");
    }
}

RE: writing to a ble characteristic

Vidar Berg — Fri, 24 May 2024 13:36:15 GMT

Yes, you need to initialize the variable after the definition.

static struct bt_gatt_write_params write_params;

write_params.handle = characteristic_handle;
write_params.data = value_to_write;
...

RE: writing to a ble characteristic

Youssef Elbattah — Fri, 24 May 2024 13:27:51 GMT

when i add static keyword to 'write_params' the handle member doesn't accept non constant value

RE: writing to a ble characteristic

Vidar Berg — Fri, 24 May 2024 13:19:00 GMT

Hello,

Please add the 'static' keyword to your 'write_params' variable definition and see if it helps. From the API documentation:

Best regards,

Vidar