[Thread]: URI missing in CoAP packet

[dipkumar_vyas]

Hello NXP Team,

We have face some issues while sending CoAP messages through the kw41z host module.

issue description is as below:

We are Using the NXP IoT gateway for our project.

We are using the FSCI protocol for communication between the thread host module and the imx6 board.

We have found some issues in the CoAP message framework. The end device does not receive the URI in the CoAP message through the thread host module.

NXP IoT gateway forming the FSCI frame for the CoAP message.
The NXP IoT gateway sends that frame to the host using the UART. After that, we found some unexpected behavior like the kw41z host module does not send the proper CoAP message in the RF for the Thread REED devices.

To solve this issue, we had done some debug:

1.We had checked the return type of CreateFSCIFrameAdHoc API. This API generates a CoAP command as per the FSCI protocol and fills it into the FSCI frame struct. We had cross-checked that structure whenever a CoAP message is forming using this API.
2.We had cross-checked the UART communication using the FTDI UART device. IoT gateway transmits proper FSCI frame for CoAP message to the kw41z thread host module. Please find the attached image for more reference.
3.We had sniffed Thread RF data using USB kw41z sniffer and Wireshark. As per the sniffer logs, we had found that the CoAP message does not have the URI in the frame.
4.We had checked with the Thread_shell application and,  we found that if the host device gets a reset message from the end devices after that, it will not create a CoAP instance. Now we have been trying to send the CoAP message manually using the terminal, but the thread host module does not send a CoAP message in the Thread RF network.

If the URI is not present in the CoAP message, then what kind of issue we faced, is described below:

1.If the Thread end device receives CoAP message without URI. The thread end device sends a Reset message to the Thread host module instead of ACK.
If the Thread host module receives a reset message from the thread end device, the host reset itself. After that, the MCU host device does not send any CoAP messages in the Thread RF network.

temporary workaround for this issue is as below:
Need to create CoAP instance for the host module using FSCI protocol.

Please help us, what is the solution for this?

Attached file description:

1.CoAP_uart_format.png:- CoAP UART communication packet(FSCI) format between NXP IoT gateway and Thread Host module.

2.wireshark_packet.png:- Sniffer packet which shows CoAP message does not contain URI

3.Thread_Shell.png:- This image shows how host modules fail to send CoAP message after getting the reset message from the Thread End device.