the extension of MTU length

[alex kim]

Hi,

My development environment is sdk12.3 s132_3.0 pca10040

I want to increase the MTU size to 64 bytes in nus.
I programmed as below, but there is no MTU size change.
It is not called with gatt_event_handler ().

/**@brief Function for handling events from the GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t * p_evt)
{
 NRF_LOG_DEBUG("ATT MTU exchange completed. central 0x%x peripheral 0x%x",
 p_gatt->att_mtu_desired_central,
 p_gatt->att_mtu_desired_periph);
}


/**@brief Function for initializing the GATT library. */
void gatt_init(void)
{
 ret_code_t err_code = nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);
 APP_ERROR_CHECK(err_code);
 
 err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 100);
 APP_ERROR_CHECK(err_code);
}

int main(void)
{
 ret_code_t err_code;
 bool erase_bonds;

 leds_init(); 

 err_code = NRF_LOG_INIT(NULL);
 APP_ERROR_CHECK(err_code);
 APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_OP_QUEUE_SIZE, false); 
 
 gpios_init(); 
 ble_stack_init();

 uart_init(); 
 peer_manager_init(erase_bonds);

 db_discovery_init();
 lbs_c_init();


 gatt_init(); 
 gap_params_init();
 conn_params_init();

 services_init();
 advertising_init();

 === omit below ====

}

Please, reply

[Philip]

Hi. Are you trying to set the MTU to 64 in this line?

err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 100);

If so are you trying to enter it in binary i.e. b'00000100' = 64?

You normally edit the MTU size in the sdk_config.h file

[alex kim]

Hi, Philip

Thank you for your reply.

I try err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 0x20);

but MTU length did not increase and gatt_evt_handler() did not be called

In sdk_config.h

- #define NRF_BLE_GATT_ENABLED 1

#define NRF_BLE_GATT_MAX_MTU_SIZE 244

In ble_nus.h

#define BLE_NUS_MAX_DATA_LEN (NRF_BLE_GATT_MAX_MTU_SIZE - 3)

Best regards,

[alex kim]

I knew the cause of the problem.

There was no gatt event processing inside the function 
static void ble_evt_dispatch(ble_evt_t * p_ble_evt)
{
   ......
    nrf_ble_gatt_on_ble_evt(&m_gatt, p_ble_evt);
    .....
}

[Stian Røed Hafskjold]

Hi, did you solve the problem?

[alex kim]

Hi, Stain

I solved it

Best regards,