Error occurred when connecting OpenThread RCP to Raspberry Pi via SPI

[Yeno Coco]

Hello~
    I used the ot-nrf528xx codebase for compilation, and according to the content in the readme, I compiled two Hex files for USB and SPI interfaces using the USB_trans and SPI_trans_NCP options, respectively. After flashing the hex file for the USB interface, it works normally as an RCP when connected to the Raspberry Pi. However, the file for the SPI interface shows no response after flashing.

    My hardware wiring is as follows:

    SPIS_PIN_MOSI P0.04 → Raspberry Pi 4B Pin19
    SPIS_PIN_MISO P0.28 → Raspberry Pi 4B Pin21
    SPIS_PIN_SCK P0.03 → Raspberry Pi 4B Pin23
    SPIS_PIN_CSN P0.29 → Raspberry Pi 4B Pin24
    SPIS_PIN_HOST_IRQ P0.30 → Raspberry Pi 4B Pin40

  Additionally, I connected the reset to Raspberry Pi Pin38 and connected GND.

  My OTBR settings are as follows:

    OTBR_AGENT_OPTS="-I wpan0 -B wlan0 spinel+spi:///dev/spidev0.0?gpio-int-device=/dev/gpiochip0&gpio-int-line=21&gpio-reset-device=/dev/gpiochip0&gpio-reset-line=20&no-reset=1&spispeed=1000000 trel://wlan0"

The current error log is as follows:

● otbr-agent.service - OpenThread Border Router Agent
Loaded: loaded (/lib/systemd/system/otbr-agent.service; enabled; preset: enabled)
Active: active (running) since Mon 2025-05-26 06:46:20 BST; 705ms ago
Process: 690205 ExecStartPre=/usr/sbin/service mdns start (code=exited, status=0/SUCCESS)
Main PID: 690215 (otbr-agent)
Tasks: 1 (limit: 3909)
CPU: 44ms
CGroup: /system.slice/otbr-agent.service
└─690215 /usr/sbin/otbr-agent -I wpan0 -B wlan0 "spinel+spi:///dev/spidev0.0?gpio-int-device=/dev/gpiochip0&gpio-int-line=21&gpio-reset-device=/dev/gpiochip0&gpio-reset-line=20&no-reset=1&spispeed=1000000" trel://w>

May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.800 [W] P-SpiIntface--: Garbage in header : 1F C0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.833 [W] P-SpiIntface--: Garbage in header : 1F E0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.866 [W] P-SpiIntface--: Garbage in header : 1F E0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.899 [W] P-SpiIntface--: Garbage in header : 1F E0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.932 [W] P-SpiIntface--: Garbage in header : 1F C0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.966 [W] P-SpiIntface--: Garbage in header : 1F E0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:25.999 [W] P-SpiIntface--: Garbage in header : 1F C0 1F FF FF
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:26.165 [W] P-SpiIntface--: Slave seems stuck.
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:26.201 [W] P-SpiIntface--: Garbage in header : F8 00 00 00 00
May 26 06:46:21 cyx otbr-agent[690215]: 63d.21:05:26.234 [W] P-SpiIntface--: Garbage in header : F9 F8 00 00 FF

Is there any step that I am doing incorrectly? I am eagerly awaiting your response. Thank you!

[Kenneth]

Hi,

I suggest to connect a logic analyzer on the relevant pins and see if you can see something that stand out. If you also have a reference implementation that works for comparison, then you can also measure that one for comparison.

Kenneth

[Yeno Coco]

Hello,

I measured the SCK signal and found that it is consistently at a low level, which is clearly abnormal, right? At the same time, I also measured the Reset signal, and it is intermittently restarting, which seems normal. Why is the SCK not changing at all？

Looking forward to your reply, thank you!

Yeno Coco

[Kenneth]

Hi,

It's not clear to me what you hardware looks like here and it's not clear to me who is doing what.

Normally for the nRF52840-DK some of the pins you are referring to is not directly available without some modifications: https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/solder_bridge.html Whether that is relevant for your problem I don't know.

I can see you write SPIS_*, this typically means that the device in question is an SPI slave, waiting for an external SPI master to execute the transfer (and toggle the SCK).

Kenneth

[Yeno Coco]

Hello,

I want to use the NRF52840 as a slave device and the Raspberry Pi as the master device to set up OTBR-RCP. I'm using the following code library:

https://github.com/openthread/ot-nrf528xx 

In the transport-config.h file, the pin configuration is defined, so I connected the pins according to this definition.

Have you used this code library to specifically achieve SPI-based communication between OTBR and RCP? If so, could you provide me with the specific steps?

Thank you very much for your response.

Yeno Coco

[Marte Myrvold]

Hi,

Have you followed the instructions under Native SPI support in the link you provided?

The code you are using is provided by OpenThread and is not made by Nordic, so if you have issues, I recommend contacting OpenThread for support:

• Bugs and feature requests pertaining to the Nordic NRF528xx example — submit to the openthread/ot-nrf528xx Issue Tracker
• OpenThread bugs and feature requests — submit to the OpenThread Issue Tracker
• Community Discussion - ask questions, share ideas, and engage with other community members

We recommend using UART or USB for the RCP and following the guide in the nRF Connect SDK documentation instead: nRF Connect SDK - Thread Border Router.

Best regards,
Marte

[Yeno Coco]

Hi

Thank you for your response. I will visit these resources for assistance. Thank you very much!

Previously, I tried using a USB connection without any issues, so I'd like to test using an SPI connection as well. Thank you for your recommendation.

Best regards,

Yeno