Zephyr direct_test_mode sample uart_poll_in() always returns -1

[snowuyl]

I tested direct_test_mode sample on nRF5340 device. But I found uart_poll_in() always return -1.

The following is debug messages of RTT Viewer.

# SEGGER J-Link RTT Viewer V7.80c Terminal Log File
# Compiled: 16:09:36 on Sep 27 2022
# Logging started @ 26 Jul 2023 13:26:21
00> [00:00:00.000,762] <inf> ipc_uart: IPC service instance opened
00> [00:00:00.001,434] <inf> ipc_uart: IPC endpoint bonded
00> [00:00:00.001,831] <inf> ipc_uart: UART ipc driver initialized for device: uart@41013000
00> *** Booting Zephyr OS build v3.2.99-ncs2 ***
00> Starting Direct Test Mode example
00> UART device is ready
00> DTM initialization ok
00> uart_poll_in() return -1
00> uart_poll_in() return -1
00> uart_poll_in() return -1

...

Procedures to reproduce this issue are as follows.

1. Unzipping direct_test_mode.zip to D:\ncs\v2.3.0\nrf\samples\bluetooth\ folder.

2. cd D:\ncs\v2.3.0\nrf\samples\bluetooth\

3. west build -b nrf5340dk_nrf5340_cpunet

4. west flash

5. Rebooting nRF5340 device and connecting to RTT Viewer.

[snowuyl]

3618.direct_test_mode.zip

[Simonr]

Hi

Due to the summer vacation period we are currently understaffed, so delayed replies must be expected. I am sorry about any inconvenience this might cause. Thank you for your patience!

You are generating very many cases in a very short amount of time. Please spend some time reading our documentation pages and debugging on your end before considering whether to make a DevZone case of it in the future, as I think multiple of them can be resolved without assistance. You also have multiple cases on this IPC service now, and it makes it hard to track the status of the issue. Please create one ticket per subject so you don't have to get the same suggestions from different support engineers multiple times. 

You're testing on a custom board, right? Have you configured the UART pins correctly on the nRF5340 side?

Best regards,

Simon