How to fragment the BLE Data

RE: How to fragment the BLE Data

Hieu — Sat, 22 Mar 2025 00:56:42 GMT

In the application core, you need these.
https://github.com/nrfconnect/sdk-nrf/blob/v2.9.1/samples/bluetooth/throughput/prj.conf#L32-L39

In the network core, you need these, but most of them should be set to such values by default.
https://github.com/nrfconnect/sdk-nrf/blob/v2.9.1/samples/bluetooth/throughput/prj.conf#L38-L44
https://github.com/nrfconnect/sdk-nrf/blob/v2.9.1/samples/bluetooth/throughput/prj.conf#L32

RE: How to fragment the BLE Data

pal_722 — Thu, 20 Mar 2025 11:37:31 GMT

My data rate is 102kbps and am I trying to achieve that in NUS,
Can you tell me what configurations specifically has to be changed ?

Thank you

RE: How to fragment the BLE Data

Hieu — Thu, 20 Mar 2025 11:08:51 GMT

Hi pal_722,

The configuration changes necessary are already discussed in this thread.

As you are on the nRF5340 DK, you need to remember that you have a network core running the BT Controller, and the application core running the host. Some configs need to be set on a specific core, and some need to be set on both. The Throughput sample also shows exactly that. You will need to pay attention to it.

Regards,

Hieu

RE: How to fragment the BLE Data

pal_722 — Thu, 20 Mar 2025 09:01:21 GMT

Hi Hieu

In my application I am trying to send 12750bytes in one second. I am currently using NUS sample on two nrf5340 dks.
What configuration changes has to be done to achieve this throughput?

I went through the throughput example, the default test case has higher data rate than my requirement.
I am expecting to get the required rate in my application too. But am confused as to what has to be done?I have been working for really long to achieve this and have failed miserably.
Your reply will be of great help!

Regards
Thank you

RE: How to fragment the BLE Data

Hieu — Mon, 10 Jun 2024 07:48:25 GMT

You can consider using asynchronous APIs for both sensor reading and BLE.

Sensor readings will be queued in callback. In your main thread/function/loop, the queue can be check, and if there is data, you send it there.

The best way is to have different threads for the job. I recommend going over our free online course on nRF Connect SDK Fundamentals, where the topic of threads is covered.

RE: How to fragment the BLE Data

Madhu Mohan Reddy — Sat, 08 Jun 2024 06:16:05 GMT

when sensor data ready pin triggers low(DRDY) ,sensor data reading function call happens and in same function I am sending data to BLE.(if Buffer is full)
if(flag == 150) send the buffer to BLE.

How can I send the data to BLE and read the sensor parellel

would you give some suggestions

Thank you

RE: How to fragment the BLE Data

Hieu — Fri, 07 Jun 2024 17:58:57 GMT

Hi Madhu Mohan,

It seems that you are new to BLE. I think it might benefit you to go over our free online course Bluetooth Low Energy Fundamentals.

[quote user="Madhan Mohan Reddy"]

Using bt_gatt_notify(); is best for sending 6000 bytes as multiple chunks?

Using bt_gatt_write_without_response(); is best?

[/quote]

Notifying is an action that only the device in Peripheral role can do.
Writing without Response is an action that only the device in Central role can do.

In your use-case, it is most likely that your device is the Peripheral, and the Android device is the Central. If this is the case, you need to use bt_gatt_notify().

[quote user="Madhan Mohan Reddy"]

CONFIG_BT_BUF_ACL_RX_SIZE=502

CONFIG_BT_ATT_PREPARE_COUNT=2

CONFIG_BT_L2CAP_TX_BUF_COUNT=10

CONFIG_BT_L2CAP_TX_MTU=498

CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y

CONFIG_BT_CONN_TX_MAX=10

CONFIG_BT_BUF_ACL_TX_COUNT=10

CONFIG_BT_BUF_ACL_TX_SIZE=502

I am bit confusing maximum we can send 495 buffer at a time or max 244 to BLE?
In throughput Sample dummy buffer is declared as 498

[/quote]

The 244 limit is to keep the GATT operation done in a single air packet. The GATT operation will be packed into a Link Layer packet, where only 244~249 bytes of GATT data can be packed.

However, a GATT operation with longer value is still possible, and it will just be split into multiple Link Layer packets. The maximum size of the GATT operation is configured by CONFIG_BT_L2CAP_TX_MTU. It is 498 by default in the Throughput sample, and likely why the dummy array is also 498.

[quote user="Madhan Mohan Reddy"]My buffer size is 150, i want 40 buffers every second ? And To read the sensor data is taking some time for spi 25 msec [/quote]

40 transfers of 150 bytes each second should be doable. The SPI read should not be a concern. Ideally you want to read the sensor and send data in parallel, not sequentially. You might want to consider using a separate thread for each job.

Hieu

RE: How to fragment the BLE Data

Madhu Mohan Reddy — Thu, 06 Jun 2024 14:08:31 GMT

CONFIG_BT_BUF_ACL_RX_SIZE=502

CONFIG_BT_ATT_PREPARE_COUNT=2

CONFIG_BT_L2CAP_TX_BUF_COUNT=10

CONFIG_BT_L2CAP_TX_MTU=498

CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y

CONFIG_BT_CONN_TX_MAX=10

CONFIG_BT_BUF_ACL_TX_COUNT=10

CONFIG_BT_BUF_ACL_TX_SIZE=502

I am bit confusing maximum we can send 495 buffer at a time or max 244 to BLE?
In throughput Sample dummy buffer is declared as 498

RE: How to fragment the BLE Data

Madhu Mohan Reddy — Thu, 06 Jun 2024 13:42:48 GMT

Hi Hieu

Using bt_gatt_notify(); is best for sending 6000 bytes as multiple chunks?

Using bt_gatt_write_without_response(); is best?

My buffer size is 150, i want 40 buffers every second ? And To read the sensor data is taking some time for spi 25 msec

How can i achieve this?

RE: How to fragment the BLE Data

Hieu — Thu, 06 Jun 2024 11:50:28 GMT

Hello Madhu Mohan,

The 6000 bytes of data you are trying to send will have to be broken down into PDUs at the GATT layer and the GAP layer.

At the GATT layer, the data has to be divided into chunks within the GATT MTU size. This must be done by the application.

At the GAP layer, the GATT PDU is divided into packets based on the negotiated Data Length between the Central and Peripheral devices. This is done automatically by the stack.

In general, the developer just needs to configure the application to support higher GATT MTU size and GAP Data Length. The particularities of these configurations have been discussed on DevZone and you will be able to find more information by searching.

For example, this is best shown by the Throughput example.

Throughput example in the nRF5 SDK: https://docs.nordicsemi.com/bundle/sdk_nrf5_v17.1.0/page/ble_sdk_app_att_mtu.html

Throughput sample in the nRF Connect SDK: https://docs.nordicsemi.com/bundle/ncs-2.6.1/page/nrf/samples/bluetooth/throughput/README.html

Hieu