Question about UART freeze when using CONFIG_LOG_BACKEND_FS on nRF5340 DK

Question

Hello Nordic team, 
 I am using an nRF5340 DK with Zephyr, and I am facing an issue where the UART console freezes whenever CONFIG_LOG_BACKEND_FS=y is enabled. 
 My logging configuration is: 
 # LOGGING
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y
CONFIG_LOG=y
CONFIG_LOG_BACKEND_UART=y
CONFIG_LOG_DEFAULT_LEVEL=3
CONFIG_PRINTK=y
CONFIG_LOG_BACKEND_FS=y
CONFIG_LOG_BACKEND_FS_AUTOSTART=y
CONFIG_LOG_BACKEND_FS_FILE_SIZE=20960
CONFIG_LOG_BACKEND_FS_FILES_LIMIT=1
CONFIG_LOG_BUFFER_SIZE=8192
CONFIG_LOG_BACKEND_FS_DIR="/lfs" 
 With the FS backend enabled, UART output stops during runtime. If I disable the FS backend, UART works normally. 
 I would like to keep FS logging enabled, so I would like to know how to configure Zephyr or the nRF5340 to avoid UART freeze when using LOG_BACKEND_FS. In other words, what settings or best practices can ensure stable UART output while FS logging is active? 
 Thank you.

Kazi Afroza Sultana · Accepted Answer

Hello, 
 You are welcome. 
 For your recent queries about mcuboot and alternative solutions I have feedback from the team. 
 1. Risk of Shrinking Slots: By reducing slot0 and slot1 to 416 KB, are there any long-term risks regarding MCUboot stability or future Zephyr SDK updates that we should be aware of? 
 We strive to keep the core parts of the SDK as small as possible, so in general applications should not increase in size between updates. So, it is good to have some extra space available, then you have the option to add future features to your own application. 
 2. Symmetry for MCUboot: We kept slot0 and slot1 at the exact same size to ensure compatibility with MCUboot "Swap" upgrades [Conversation History]. Is this the recommended approach when repartitioning internal flash? 
 MCUboot has a hard requirement on that its slot has the same sizes for SWAP upgrades. 
 3. Alternative Solutions: Are there better best practices for increasing storage capacity on the nRF5340 DK (e.g., using the external flash on the DK via QSPI) that would avoid shrinking the primary application slots? 
 For the nRF5340DK, external flash is frequently used when we need more flash. For example, this is what we do when we enable FOTA in Simultaneous updates for both cores of the nRF5340 .

Question about UART freeze when using CONFIG_LOG_BACKEND_FS on nRF5340 DK

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