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doc: logging: Add section about LOG_PRINTK option

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Add section which describes coexistence of printk and logging
and the behavior of LOG_PRINTK with information that it is by
default enabled.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
This commit is contained in:
Krzysztof Chruscinski 2022-11-29 09:48:41 +01:00 • committed by Carles Cufí
commit 3a6e769070
1 changed files with 16 additions and 0 deletions
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16
doc/services/logging/index.rst
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@ -343,6 +343,22 @@ When :c:func:`log_panic` is called, _panic_ notification is sent to all active
backends. Once all backends are notified, all buffered messages are flushed. Since
that moment all logs are processed in a blocking way.
.. _logging_printk:
Printk
******
Typically, logging and :c:func:`printk` is using the same output for which they
compete. This can lead to issues if the output does not support preemption but
also it may result in the corrupted output because logging data is interleaved
with printk data. However, it is possible to redirect printk messages to the
logging subsystem by enabling :kconfig:option:`CONFIG_LOG_PRINTK`. In that case,
printk entries are treated as log messages with level 0 (they cannot be disabled).
When enabled, logging manages the output so there is no interleaving. However,
in the deferred mode it changes the behavior of the printk because output is delayed
until logging thread processes the data. :kconfig:option:`CONFIG_LOG_PRINTK` is by
default enabled.
.. _log_architecture:
Architecture