nRf54L15多连接透传通信速率是否可达到5KB/s

RE: nRf54L15多连接透传通信速率是否可达到5KB/s

Edvin — Thu, 29 Oct 2026 13:05:57 GMT

Hello,

Do you see anything from your logs? Any error messages?

When you add BLE, what happens is that the bluetooth stack and SoftDevice controller generates interrupts, so the UART doesn't get access to the CPU 100% of the time.

I thought I understood your application, but now I am no longer sure.

You have one central and 3 peripherals, right?

Is the central only an nRF54L15, or is it another MCU? For some reason I thought this was an HCI application, but apparently it is not.

So it is your application that handles both BLE and UART, right?

Since you are using the UART for your application, try enabling RTT logging and see if any errors or warnings are reported in the log.

Best regards,

Edvin

RE: nRf54L15多连接透传通信速率是否可达到5KB/s

CharlesZhuo — Thu, 29 Oct 2026 01:39:34 GMT

Edvin

Thank you very much for your reply. I am aware that the baud rate of 115,200 is too low; I am currently debugging and will change the baud rate to 921,600.

Regarding BLE connection parameters and MTU values.The BLE connection parameters are 20–40 ms; its latency is 0, and the connection timeout is 4 seconds. The MTU value is 244.

I am currently testing a baud rate of 921,600; once BLE is connected, I will simply test whether data loss occurs during UART communication.

Testing method:

Upon receiving data via the UART interrupt, the data is immediately returned through the UART.Using the Serial Debug Assistant, send 1,000 bytes of data to the nRF54L15 module in a loop at 20 ms intervals; upon receiving the data, the module immediately returns it.

Issue :

When the BLE connection is inactive, the aforementioned test method confirms that no data loss occurs during UART communication; however, when the BLE connection is active, the same test method reveals that a few bytes of data are lost during UART communication.

The UART driver code is referenced from the example in samples/drivers/uart/passthrough in ncs3.1.1.

RE: nRf54L15多连接透传通信速率是否可达到5KB/s

Edvin — Wed, 28 Oct 2026 13:46:52 GMT

Hello, and thank you for the translation. It is a little more detailed than my google translate translation 🙂

1: It is not entirely clear to me how much data goes in both directions, but let us say that you transmit 128 bytes to 3 devices every 25ms:

128bytes/message * 8bits/byte * 3 devices * 40 messages/second = 122880 bits per second. And that is without the replies from the peripherals back to the central. Already you are over 115200

Then, every byte on uart has a stop bit and perhaps a parity bit, so it is really more like 10 bits per byte of actual transfer time.

Then you have some additional data. There is more UART data than the actual payload bytes between the host and the controller. And there is more packets than just the payload that you want to send. So indeed, 115200 is too slow.

2: I am not too familiar with this sample yet, but I suspect that you are dealing with some queuing issues, so I suggest we look into issue 1 first. Try increasing the baudrate to 921600, or perhaps even 1000000.

Regarding BLE throughput, 3 devices with 128 bytes every 40ms should be fine, but to be sure, please tell me more about your connection parameters. What is your connection interval and MTU?

But with the correct parameters, this is perfectly doable. 128 bytes is only one packet if the MTU is sufficiently high. Also, data loss over BLE is almost impossible. Packets will be retransmitted forever, until it is either ACKed or the connection drops. So if you are loosing data between one end and the other, it is probably over the UART link on one of the sides (probably the central, with most traffic).

Best regards,

Edvin

RE: nRf54L15多连接透传通信速率是否可达到5KB/s

CharlesZhuo — Wed, 28 Oct 2026 02:34:02 GMT

Okay; below is the description of the question in English.

Can the multi-connected bidirectional transparent communication rate of nRf54L15 reach 5 KB/s?

Prerequisites:

Based on the nRF54L15 chip and nRF Connect SDK (NCS) v3.1.1, implement multi-connection BLE functionality where a device acts as both a central and a peripheral; support bidirectional transparent data transmission while the central device is connected to three peripherals.Additionally, an isochronous channel feature has been added to the master-slave integrated firmware.

Detailed description:

After the BLE host module has connected three BLE slave modules, the communication baud rate between the MCU and the BLE host is 115,200, and the communication baud rate between the MCU and each of the three BLE slave modules is also 115,200.

Under these conditions, the MCU sends 128 bytes of transparent data to the BLE host module at 25 ms intervals; upon receiving the data from the MCU, the BLE host directly forwards it to the three slaves. When a BLE slave receives data sent by the BLE host, it forwards the data to the MCU; upon receiving data sent by a BLE slave, the MCU immediately returns the original data to that slave.

Add an isochronous channel to the master–slave integrated firmware; its function is to implement the functionality described in the iso_central example, the iso_peripheral example, and the conn_time_sync example in ncs3.1.1; enable the BLE master–slave isochronous channel to output pulses at a rate of 100 ms on pin P1.02.

Issue Details：
1. In BLE's bidirectional transparent communication with one master and three slaves, transmitting 128 bytes at 25 ms intervals yields a rate of 5.12 KB/s; with a baud rate of 115,200, the maximum communication rate can reach 11.52 KB/s.However, when the bidirectional transparent communication rate between the BLE master and three slave devices is 5.12 KB/s, data loss occurs upon receipt by the BLE master and slaves.
2. During transparent communication in a BLE master–slave configuration, the pulse waveforms output by the BLE master and slave on the isochronous channel pins may become unsynchronized; for details, please refer to the image below.

Edvin

Regarding your inquiry about data loss caused by the throughput of the baud rate of 115,200 reaching its limit, I have taken this into consideration and plan to change the baud rate to 921,600; however, I would like to confirm whether, when operating in BLE multi-connect mode with bidirectional throughput, the data rate can reach 5 KB/s.

When performing multi-connected bidirectional transparent transmission at a rate above 5 KB/s, could this cause insufficient cache space or delayed processing in the BLE protocol stack, thereby leading to data loss?

Regarding the ISO time synchronization pins: it is isochronous channel pins.

RE: nRf54L15多连接透传通信速率是否可达到5KB/s

Edvin — Tue, 27 Oct 2026 23:39:07 GMT

Hello,

Please use the english language, as this is what we are using here on DevZone.

Could it be that you are pushing what you are able to acheive using the default 115200 baud rate on your UART? You say that you are loosing data. Do you know if that is received over BLE, but lost over UART? Or where do you mean that it is lost?

2. How can I prevent the BLE transparent data transmission from interfering with the waveforms on the ISO time synchronization pins?

I am not sure what you mean here. Can you please explain?

Best regards,

Edvin