RAK3172 RUI3 Boot mode issue


Currently I’m facing an problem with the RAK3172 with latest firmware (RUI3). The boot mode gets activated without double clicking (pulling to GND) the reset pin, boot mode gets activated randomly. Also it is not possible to exit the boot mode with the at+run command. The only way to temporarily resolve the problem is by flashing the RUI3 firmware again. Until the boot mode gets somehow triggered again. Is there a way to resolve this problem?


Hi @arne ,

Can you share the RUI3 version you have via AT+VER=? command. The version with boot mode issue is RUI3 version 3.4.2 build 112.

If you have 3.4.2, the issue can be rooted on the double-click reset or the profile of the power supply ramp during power up. We will release a firmware very soon that solves this issue.

If you can hook an oscilloscope on the reset pin, that will be helpful to verify. There are cases that some ringing supply voltage during power up looks like a pulses in the reset pin which causes the activation of boot mode.

Hi Carl,

The AT+VER command returns AT+VER=3.4.2-rui3_22q1_update.112

So we are using an affected version. Is there a temporary solution, for example downgrading to an older RUI3 version?

I don’t have a oscilloscope at hand at this moment. Will check it with our pcb designer shortly.


Hi @arne ,

I had a second look on your original message. You said, at+run doesn’t work. Did you try these at+run and AT+RUN?

We will release a new firmware soon that will have a fix. I am patiently waiting for this update as well :pray:

Hi @carlrowan,

Thanks for your reply. The devil is in the details. I’ve checked the code and we are sending AT+RUN.
(static uint8_t ATC_AT_RUN = {“AT+RUN”}:wink:
Is it needed to power cycle the module after sending this command? Or should it restart automatically?

How do I know when a new firmware is available? Looking at the current download I don’t see a version number but just the following filename “RAK3172-E_latest.bin”.



No need to reset at+run should be ok :+1:

The latest firmware version is the most recent one listed on the CHANGELOG.md in our download site.

This will likely be updated early next month. But no promises. I am patiently waiting too.

Hi Carlo,

We are still struggling with the boot mode issue. The PCB designer has tested the board with a oscilloscope hooked up to the reset pin. No pulses during startup have been detected.

So we are considering to downgrade to RAK3172_v1.0.3_Boot+App_20211021 version, which looks more stable during the first tests. Or should we wait for the new firmware release?



Hi @arne ,

I won’t recommend to downgrade to the legacy firmware because we do not actively support it anymore. Maybe you can use this for now - Dropbox - RUI_3.5.1_RAK3172-E.bin - Simplify your life

You can update via RAK DFU Tool. Please note that this is not yet official release but the bootloader mode bug is already fix so you won’t need at+run anymore.

Hi Carlo,

Thanks for sharing this pre-release :slight_smile:

We are using swd to program the rak module ( segger jlink->segger-jflash lite) apparently it is not possible to write bin files this way. Is it possible to also share the .hex version?

Thanks for your help!

Kind regards,


You can actually use RAK DFU Tool to upload the bin file.

But if you prefer the hex file via jlink here it is - Dropbox - RUI_3.5.1_RAK3172-E_final.hex - Simplify your life


Currently I’m facing an problem with the RAK3172 . In Boot Pin I have connected 3.3V , Connected Uart2 Pins to Uart to TTL(USB). Using STM32 Cube Programmer by selecting Uart and Clicked Connect it is showing Error like:
Serial Port COM1 is successfully opened.
11:58:08 : Port configuration: parity = even, baudrate = 115200, data-bit = 8, stop-bit = 1.0, flow-control = off
11:58:10 : Timeout error occured while waiting for acknowledgement.
11:58:10 : Timeout error occured while waiting for acknowledgement.
11:58:10 : Error: Activating device: KO. Please, verify the boot mode configuration and check the serial port configuration. Reset your device then try again…

Is there anything else needs to check in the circuit.


Welcome to RAK forum @JeganTom ,

It seems you are trying to connect to COM1. Can you confirm that your USB-Serial converter is really using COM1 and not other COMx port?

Hello @carlrowan ,
USB-Serial converter is COM7 which I am currently using and I had selected the correct COM7 port and Baud Rate is 115200. My main doubt is regarding the circuit, is there any additional connections required in circuit

If the BOOT pin is already 3.3v level then you reset the module, then it should be detected with the UART connections.

Few issues possible:

  1. Jumper wires related.
  2. Interchanged RX and TX.
  3. USB cable issue (if you use one).
  4. USB port.

Another thing you can try is to lower the baud rate.