BLE_NUS_MAX_DATA_LEN and buffer size question

[Pawel Niedbala]

Hi!

What's the difference between UART_TX_BUF_SIZE and BLE_NUS_MAX_DATA_LEN in case of ble_app_uart example?

As I have noticed BLE_NUS_MAX_DATA_LEN determines maximum length of data sent over BLE, for example BLE_NUS_MAX_DATA_LEN=244, I can send up to 244 bytes.

But I don't know how does buffer size affect performance, maximum length and so on. Why is it set to =256 (along with RX_buffer) by default, and not =8?

[Vidar Berg]

Hi, 

UART_TX_BUF_SIZE is the SW FIFO buffer allocated to the UART interface, while BLE_NUS_MAX_DATA_LEN defines the max. data length for BLE packets as you already pointed out.

Throughput is typically higher on the UART interface compared to the BLE link so it may make sense to have a larger buffer for the UART in order to keep data while waiting for it to be transmitted over BLE.  

  

[Pawel Niedbala]

Hi! Thanks for the answer.

So when I do use NUS service (only sending data over BLE) but I don't really want to use serial terminal and print it, I shouldn't even bother setting buffer size. Am I right?

[Håvard]

Correct, UART_TX_BUF_SIZE is only interesting if you are using the uart hardware peripheral (for example to interface a terminal on your pc), not if you are only using the Nordic UART Service to send data on air between two devices.