Thingy91X UART Shell drops characters at 921600

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Fri, 19 Dec 2025 22:23:31 GMT

Hi Hakon,

I tried the Nordic Serial Terminal (v1.6.0) with the Thingy91X and I was not able to get it to work. It has the same problem as with minicom and picocom, I cannot send characters to the Thingy shell. I confirmed that the same software build for the `nrf9151DK` works correctly with all three terminal emulation programs (minicom, picocom and Nordic Serial Terminal).

We have changed our development configuration to only use 115200 baud to work around the dropped characters. I think the lack of flow control on this port causes the problem at 921600 baud, but I do not know why we did not observer it with earlier releases of NCS.

Today I tried NCS v3.2.1 and found that the Thingy91X problem no longer occurs with any of the three terminal emulation programs.

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Tue, 02 Dec 2025 09:26:43 GMT

I did some more testing, this time using picocom. And using that I was not able to send anything. Could be that you need to change some settings with minicom to make it work. With the Nordic Serial Terminal it worked with 115200.

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Mon, 01 Dec 2025 16:26:46 GMT

I tried with v3.2.0-rc1 and yes, it seems very bugged. At least on 1M baud. At 115200 baud it worked fine. I will do some more testing tomorrow.

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Mon, 01 Dec 2025 08:03:26 GMT

[quote user="Neal Riedel"]Can you try that experiment?[/quote]

Yes, I will try to replicate and report back.

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Fri, 28 Nov 2025 19:35:05 GMT

Hi Hakon,

I tried 1M baud on the Thingy. Unfortunately, it still does not work. The result was the same if flow control was on or off in the DTS.

I also went back to the v3.2.0-preview3 tag in NCS. I found that it still does not work at all, I cannot send chars to the Thingy91X shell, even at 115200. Can you try that experiment? If it works for you, maybe you could send me your HEX file and I can try it to possibly eliminate any possible HW problems.

Thanks,

Neal

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Tue, 25 Nov 2025 08:02:18 GMT

Can you try testing with 1M baud instead? That has been tested to work with the thingy91x, and is also an exact value. In the case of 921600 baud, what is actually being used is 2 % higher, which could lead to errors when going through the connectivity bridge.

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Thu, 20 Nov 2025 21:29:16 GMT

I tried enabling the HW flow control and the problem remained. I expected this because I do not believe the HW flow control signals are connected between the nrf9151 and the board controller on the thingy91x.

For the record, here is the DTS overlay I used:

/*
    Thingy91X board DTS Overlay
*/

/ {
    aliases {
                uart0 = &uart0;
                uart1 = &uart1;
    };
};

&uart0 {
        status = "okay";
        hw-flow-control;
};

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Wed, 19 Nov 2025 09:03:20 GMT

[quote user="Neal Riedel"] I checked and HW flow control is not enabled in the DTS.[/quote]

Can you try with flow control enabled?

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Mon, 17 Nov 2025 17:06:23 GMT

Hi Hakon,

I tried disabling CONFIG_UART_NRFX_UARTE_LEGACY_SHIM. Unfortunately, the results were the same. The console still drops characters at 921600. I did notice that with this config disabled, the console sometimes became unresponsive for several seconds after dropping characters. That is, typing on the keyboard gave no update on the console. This did not happen with CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y.

I also tried updating to the v3.2.0-preview3 tag in NCS. I found that this tag would not work at all, even at 115200 baud. I could not enter characters on the modem shell. I could see the output logs, but there was no response to the input characters. I reverted the code to the revision I was previously using (81daeb705c4cfadfd8c890c802a9d30ce15323b7) and it worked OK at 115200. Of course, I did the usual west update after checking out a different tag/revision.

I repeated the experiment, and found the behavior was consistent. That is, the v3.2.0-preview3 tag would not respond to characters on the input console, while the 81daeb705c4cfadfd8c890c802a9d30ce15323b7 revision would. I did notice that when switching back to the 81daeb705 revision, I had to use west flash --recover to get the device to program. Perhaps this is a clue to this issue.

Thanks,

Neal

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Wed, 12 Nov 2025 16:31:06 GMT

Hi Hakon,

Thank you for your response. I checked and HW flow control is not enabled in the DTS. The CONFIG_UART_NRFX_UARTE_LEGACY_SHIM config is enabled. I will try disabling it. Unfortunately, I am out of the office for the rest of this week. So I will post the results here early next week.

Thanks,

Neal

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Wed, 12 Nov 2025 12:47:31 GMT

Also, if not already disabled, can you disable this?

CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=n

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Wed, 12 Nov 2025 12:25:05 GMT

Do you have flow control enabled in dts? You should check if this is somehow enabled when building for v2.8.

RE: Thingy91X UART Shell drops characters at 921600

Neal Riedel — Mon, 10 Nov 2025 15:39:42 GMT

Hi Hakon,

I tried updating the connectivity bridge as you suggested. Unfortunately, the problem still remains. At the 921600 baud rate, we see dropped characters when pasting "shell backspace_mode delete" into minicom:

mosh:~$ shell backspac_modedelete

As you can see, several characters are lost.

It is curious that we do not see this problem with the older v2.8 NCS version.

Thanks,

Neal

RE: Thingy91X UART Shell drops characters at 921600

Hakon — Mon, 10 Nov 2025 14:41:36 GMT

Hello,

can you try updating connectivity bridge to -> https://github.com/hello-nrfcloud/firmware/releases/download/v3.0.1/connectivity-bridge-v3.0.1-thingy91x-nrf53-dfu.zip

nrfutil device program --firmware ..-dfu.zip --traits mcuboot