gatt_evt_handler config to set data length to send data by uart

[Renato Silva]

Hi,

I am adapting the uart example to send mensages between central and peripheral using JSON. In this moment I can send central <------>peripheral... 

I have a problem because there are a limitation to send string, the data length max is 61 characters.. any value biggest than 61, is send in another message. So when I want to parse message (in the receiver size) I can read only the first 61 characters. The remaining I lost...

I saw that the gatt_evt_handler method sets the m_ble_nus_max_data_len and this variable define the data size that will be send (uart_event_handle)

if ((data_array[index - 1] == '\n') || (index >= (m_ble_nus_max_data_len)))

Are there any way to send data string biggest than 61 characters in only one message??

[Martin Lesund]

Hello Renato,

The question is how many characters you are trying to send? 

A little more information of what you are trying to  achieve would be highly appreciated. 

A proposal is to increase the MTU size on both the peripheral and central side. 

If you look at the "ble_app_uart" example and take a look in the gatt_init() you can see how this is handled on the peripheral side (nrf_ble_gatt_att_mtu_periph_set()). 

(similar Thread about MTU size)

[Renato Silva]

Hello Martin,

Martin Lesund said:

The question is how many characters you are trying to send? 

I want to send a json, and in my solution this structure does not size defined. The size can be between 10 and 255, for example.

Martin Lesund said:

A proposal is to increase the MTU size on both the peripheral and central side. 

Where I can to do it?

Martin Lesund said:

If you look at the "ble_app_uart" example

I am working in this example..

[Martin Lesund]

Hi Renato,

You can use the function nrf_ble_gatt_att_mtu_periph_set() (for peripheral side) as described at last post.

You can also take a look at the "ATT_MTU Throughput Example" for reference on how this is handled. Also here is a blog post describing the different parameters.

[hmolesworth]

As Martin says, the key is gatt_init() - see line 488 where 61+3=64 and change from

<p>err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 64);</p>

to
<p>err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, NRF_SDH_BLE_GATT_MAX_MTU_SIZE);</p>