GATT Server - Write or Write without Response characteristic sample

[pekon94]

Hello,

is there a zephyr or nrf sample where I could check how a characteristic with write or write_withour_resp perimissions is handled by the gatt server ?

What I am trying is to find out how the gatt server can process the data written by a gatt client.

Thank you in advance

[Kenneth]

Hello,

The nus example show usage of write and the throughput example show usage of write without response:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/central_uart/README.html 
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/peripheral_uart/README.html 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/throughput/README.html 

Hint:

Typically the GATT client can use bt_gatt_write_without_response() or bt_gatt_write(). The GATT server must add support for either or both using BT_GATT_CHRC_WRITE | BT_GATT_CHRC_WRITE_WITHOUT_RESP when calling BT_GATT_CHARACTERISTIC().

Best regards,
Kenneth

[pekon94]

Hello Kenneth,

thank you for  your assistance. 

I tried to use the throughput sample as a reference for how to process the data written by the client but was not successful.

I am using a write_callback function declared in the BT_GATT_CHARACTERISTIC() to get the attr->user_data and store in a uint16_t variable. 

Is the data written by the client temporarily stored in the user_data parameter of the bt_gatt_attr structure attr ? 

[Kenneth]

pekon94 said:

Is the data written by the client temporarily stored in the user_data parameter of the bt_gatt_attr structure attr ? 

Yes, so you must memcopy it to your own array.

Kenneth

[pekon94]

Hello Kenneth,

this is how I have used the BT_GATT_CHARACTERISTIC:

BT_GATT_CHARACTERISTIC(BT_UUID_FSR, BT_GATT_CHRC_WRITE_WITHOUT_RESP,
                       HRS_GATT_PERM_DEFAULT & GATT_PERM_WRITE_MASK,
                       NULL, write_callback, &user_dt),

and this is the write_callback function:

static ssize_t write_callback(struct bt_conn *conn, const struct bt_gatt_attr *attr,
                 void *buf, uint16_t len, uint16_t offset, uint8_t flags)
    {
        uint16_t write_data ;
        memcpy(write_data, attr->user_data, sizeof(attr->user_data));
        printk("HRS CONTROL POINT is %u\n", write_data);
        printk("HRS CONTROL POINT is %u\n", &write_data);
            printk("HRS CONTROL POINT is %u\n", attr->user_data);
            printk("HRS CONTROL POINT is %u\n", user_dt);
    }

I am testing by writing a uint16_t value, but I am not able to see the same value in the printk result.

[Kenneth]

Considering you don't really know if the erronous data is due to central or peripheral, then I suggest you capture on-air sniffer so you may check the data first:
https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE

Kenneth