nrf52811 bluetooth concept

[nordicDK]

Hi all, 

I want to fully understand the concept of Bluetooth protocol using nrf52811. Any advice will be helpful for me!

First, as I understand softdevice is Bluetooth API that help developer to easily apply the Bluetooth protocol, is it right? Then which version of softdevice is optimal for nrf52811?
From below website S112, S113, S140, S122  is possible. Then why not always use the most recent SoftDevice? What are the reasons for choosing a smaller or older one instead? What are the key differences between each SoftDevice, such as Flash and RAM requirements, and are there other important factors to consider?
https://www.nordicsemi.com/Products/nRF52811/Download 

Second, I want to calculate the maximum data transfer bps of nrf52811. Then I found the concept, MTU, connection interval, DLE(data length extension), gap event length, PHY, packet per event. From my understanding, the key factors affecting throughput are the MTU size, connection interval, and the number of packets per connection event. 
For example, if MTU = 247 bytes, 4 packets are sent per connection, connection inetval = 15ms
247*8*4 / 0.015 = 526,933 bps. Then I have two question

• The official documentation says that the nRF52811 supports 2 Mbps. Does this mean that it can actually achieve 2 Mbps throughput? Or is that just the maximum physical layer (PHY) speed, and actual throughput will be much lower?
  www.nordicsemi.com/.../Download

• When using the nRF52811 with the S140 SoftDevice, how can I find out the maximum supported values for:

  • MTU size

  • Data packet size

  • Connection interval

"Ultimately, what I want to understand is how to calculate the maximum data throughput when using the nRF52811."

Finally, it would be thankful to recommend me the document or youtube link that summarize this concept very well.

Thank you!

[tesc]

Hi,

The SoftDevice is an implementation of the Bluetooth stack. Through using either the SoftDevice API, or libraries on top of that API, you can build applications using Bluetooth.

Please note that for new projects we recommend not to use the older nRF5 SDK with SoftDevice, but rather the newer nRF Connect SDK. The Bluetooth stack is continued in nRF Connect SDK, but now as the "SoftDevice Controller". The Bluetooth stack can be split in Controller and Host, and with nRF Connect SDK the SoftDevice Controller is based off of the lower layers of the SoftDevice. For more information on SDK selection, please see our nRF Connect SDK and nRF5 SDK statement.

Then which version of softdevice is optimal for nrf52811?

We highly recommend to instead go for nRF Connect SDK. There, there is no choice of which SoftDevice to use, but rather the required functionality is included based on configuration of which roles and features is needed by the application.

From below website S112, S113, S140, S122  is possible. Then why not always use the most recent SoftDevice?

The different variants of the SoftDevice had different feature sets, e.g. peripheral only, central only, or support for both peripheral and central roles.

The official documentation says that the nRF52811 supports 2 Mbps. Does this mean that it can actually achieve 2 Mbps throughput?

This is the baud rate when sending data for one packet, and not the final throughput. BLE is not a continuous stream of bits. For advertisements, short packets are sent with typically relatively long intervals in-between. For connections, packets are sent back and forth between two devices during what is called a connection event, and then there is typically a longer interval until the next connection event. Data is sent in one direction at a time during the connection event.

Finally, it would be thankful to recommend me the document or youtube link that summarize this concept very well.

For a solid understanding of Bluetooth Low Energy, we highly recommend the Bluetooth Low Energy Fundamentals course on DevAcademy. You might want to have a look at nRF Connect SDK Fundamentals as well, to get started with the SDK. DevAcademy is free of charge and part of the documentation and customer support provided by Nordic Semiconductor.

Regards,
Terje