RE: How to correctly set MTU size in Nordic Connect SDK V2.0?

MehdiZ — Wed, 20 Jul 2022 13:49:57 GMT

Thank you for your help.

I tested the peripheral_uart as is and it works correctly although there are some warnings during build phase

warning: BT_CTLR_DATA_LENGTH_MAX (defined at
/opt/nordic/ncs/v2.0.0/nrf/subsys/bluetooth/services/fast_pair/Kconfig.fast_pair:83,
/Users/mehdizemzem/nRF53/peripheral_uart_throughput/build/subsys/bluetooth/controller/Kconfig:379) was assigned the value '251' but got the value ''. Check
these unsatisfied dependencies: ((BT_FAST_PAIR_GATT_SERVICE && BT_FAST_PAIR && BT) ||
(BT_CTLR_DATA_LENGTH && BT_CONN && BT_CTLR && BT_HCI && BT)) (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_BT_CTLR_DATA_LENGTH_MAX and/or look up
BT_CTLR_DATA_LENGTH_MAX in the menuconfig/guiconfig interface. The Application Development Primer,
Setting Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be
helpful too.


warning: BT_SETTINGS (defined at /Users/mehdizemzem/nRF53/peripheral_uart_throughput/build/subsys/bluetooth/host/Kconfig:169,
/Users/mehdizemzem/nRF53/peripheral_uart_throughput/build/subsys/bluetooth/host/Kconfig:169) was assigned the value 'y' but got the value 'n'. Check these
unsatisfied dependencies: ((SETTINGS && BT_HCI_HOST && BT_RPC_STACK) || (SETTINGS && BT_HCI_HOST &&
BT_HCI && BT)) (=n). See http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_BT_SETTINGS and/or
look up BT_SETTINGS in the menuconfig/guiconfig interface. The Application Development Primer,
Setting Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be
helpful too.


warning: BT_PRIVACY (defined at /Users/mehdizemzem/nRF53/peripheral_uart_throughput/build/subsys/bluetooth/host/Kconfig:322,
/Users/mehdizemzem/nRF53/peripheral_uart_throughput/build/subsys/bluetooth/host/Kconfig:322) was assigned the value 'y' but got the value 'n'. Check these
unsatisfied dependencies: ((BT_SMP && BT_CONN && BT_HCI_HOST && BT_RPC_STACK) || (BT_SMP && BT_CONN
&& BT_HCI_HOST && BT_HCI && BT)) (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_BT_PRIVACY and/or look up BT_PRIVACY in the
menuconfig/guiconfig interface. The Application Development Primer, Setting Configuration Values,
and Kconfig - Tips and Best Practices sections of the manual might be helpful too.

I retested my code with the nRF BLE desktop app and this is the log I have for now:

14:27:27.705	Scan started
14:27:29.207	Connecting to device
14:27:30.028	Connected to device F6:2B:E4:76:38:34: interval: 7.5ms, timeout: 4000ms, latency: 0
14:27:30.070	Data length updated for device F6:2B:E4:76:38:34, new value is 251
14:27:30.156	Phy updated for device F6:2B:E4:76:38:34, tx: 2 Mb/s, rx: 2 Mb/s
14:27:30.315	Attribute value read, handle: 0x0B, value (0x): 5A-65-70-68-79-72
14:27:34.401	Attribute value changed, handle: 0x13, value (0x): 01-00
14:27:34.407	Attribute value written, handle: 0x13, value (0x): 01-00
14:27:35.078	Connection parameters updated for device F6:2B:E4:76:38:34: interval 12.5ms, timeout 30000ms, latency: 0

Can you recommend another sniffer to use?

On the bright side, I solved my problem by adding the following functions to my code:

static int update_connection_parameters(void);
static void request_mtu_exchange(void);
static void request_data_len_update(void);
static void request_phy_update(void);
static void MTU_exchange_cb(struct bt_conn *conn, uint8_t err, struct bt_gatt_exchange_params *params);
static void le_phy_updated(struct bt_conn *conn,
			   struct bt_conn_le_phy_info *param);
static void le_data_length_updated(struct bt_conn *conn,
				   struct bt_conn_le_data_len_info *info);

I suppose that what you said is correct about the ATT MTU negotiations

RE: How to correctly set MTU size in Nordic Connect SDK V2.0?

Hung Bui — Wed, 20 Jul 2022 11:48:09 GMT

Hi Mehdi,
You may want to capture a sniffer trace so we get to understand what happens over the air.
I suspect that the ATT MTU negotiation didn't happen and you don't have the MTU = 247 so you can't send the notification of that size.
Note that the throughput example requires the control from both sides. Actually it's the central that request the ATT MTU update.

I have made a blog and an example to test throughput. You can have a look here. The example when act as a peripheral will pro-actively request ATT MTU exchange to increase the MTU.