nRF Connect SDK NUS throughput modifications and issues for peripheral_uart/central_uart example applications

[mtsunstrum]

There are many questions on DevZone on modifications to NCS peripheral_uart/central_uart NUS example applications to support higher throughput.

We have been mostly successful in modifying both applications so that BLE throughput can operate at 1380-1400 kbps.

After peripheral_uart/central_uart establish a connection, the central_uart will setup link parameters to improve BLE throughput:

• negotiate to use 2M PHY
• negotiate to use DLE (data length extension) set to 251 bytes
• negotiate to use connection interval of 400ms

The UART has been modified to run at maximum speed of 1000kbps.

This work was done on NCS 1.8.0, but also demonstrated on NCS 1.6.1 and 1.7.1

It has been tested on nRF5340-DK and nRF52832-DK boards.

In the attached file nus_throughput_test_repo.zip there is a Git repo which shows all the code/project modifications, starting from the original NCS peripheral_uart/central_uart example applications. Fairly straightforward to see all the modifications.

If you build them, they will operate in a BLE throughput test mode, ignoring any UART communications.

After connecting and exchanging link negotiations, the peripheral_uart will send a 240 byte message as fast as possible, and central_uart will put out periodic RTT logs indicating the BLE received data rate of approximately 1380-1400 kbps

The throughput is perfect ( assuming your are in a clean RF environment )

One problem we have though is the following:

• in present central_uart application (main.c), we have defined #define BLE_NUS_DISABLE_BT_CONN_SECURITY for our own purposes
• this #define BLE_NUS_DISABLE_BT_CONN_SECURITY will make sure central_uart does not establish link security
  • via bt_conn_set_security(conn, BT_SECURITY_L2)

But if one sets #undef BLE_NUS_DISABLE_BT_CONN_SECURITY, the link security will be successfully established. Both endpoints will operate at 1380-1400 kbps throughput but with one important caveat / odd behavior.

• What we observed is that every 28-29 seconds, the link communications will stumble
• At this time, the throughput will drop drastically for upwards of 1200 ms ... a long time !
• Then it will recover to perfect throughput, and this process will repeat every 28-29 seconds.

It appears there is something in the security/encryption mechanism that is responsible for this periodic throughput impairment.

Any ideas in the DevZone world on this issue ?

Issue appears to exist in NCS 1.6.x through to NCS 1.8.x

Thanks for your help !

nus_throughput_test_repo.zip

[Simonr]

Hi again

Seeing as it is so consistent (every ~28.8 seconds or so, 30 seconds with the 1200ms delay) it's most likely a connection parameter timeout somewhere, but I'm not able to find one matching this in the project you provided. I can't think of what it could be that trigs every 30 second, but there must be something.

You can also try adding some more logging to see if you're able to get some information other than the UART printing. Try logging the BT_CONN_SECURITY process, and perhaps add a way to see an error code from the UART peripheral so we can get more info of what exactly is causing this error.

I will test on my work computer on Monday (I'm restricted to home office due to CoVID atm), as I'm struggling to follow the connection while sniffing for the device for some reason. Hopefully I won't have this issue at my work computer.

I also see that you use the JUST WORKS security, so setting a passkey should not be necessary.

Best regards,

Simon

[mtsunstrum]

Hi @Simonr ok, good you can re-create the issue.

I did enable some logging ...

CONFIG_BT_DEBUG_CONN=y          This did not yield anything information
CONFIG_BT_LOG_LEVEL_DBG=y    This caused a flood of messages, but RTT via nRF5x-DK would drop too many messages.

I can look at BT_CONN_SECURITY ...

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Other notes:

You mentioned: perhaps add a way to see an error code from the UART peripheral

That code is there already but the peripheral_uart function bt_nus_send() always return a success code.

You mentioned: it's most likely a connection parameter timeout somewhere, but I'm not able to find one matching this in the project you provided.

Keep in mind, these are effectively "stock" NCS example applications ( central_uart, peripheral_uart ). The most minimalistic changes have been made to support enhanced BLE throughput.