At compile time, filtering is done using ``CONFIG_LOG_DEFAULT_LEVEL`` macro, set via menuconfig. All logging statements for levels higher than ``CONFIG_LOG_DEFAULT_LEVEL`` will be removed by the preprocessor.
At run time, all logs below ``CONFIG_LOG_DEFAULT_LEVEL`` are enabled by default. ``esp_log_level_set`` function may be used to set logging level per module. Modules are identified by their tags, which are human-readable ASCII zero-terminated strings.
Additionally there is an _EARLY_ variant for each of these macros (e.g. ``ESP_EARLY_LOGE``). These variants can run in startup code, before heap allocator and syscalls have been initialized. When compiling bootloader, normal ``ESP_LOGx`` macros fall back to the same implementation as ``ESP_EARLY_LOGx`` macros. So the only place where ``ESP_EARLY_LOGx`` have to be used explicitly is the early startup code, such as heap allocator initialization code.
(Note that such distinction would not have been necessary if we would have an ``ets_vprintf`` function in the ROM. Then it would be possible to switch implementation from _EARLY_ version to normal version on the fly. Unfortunately, ``ets_vprintf`` in ROM has been inlined by the compiler into ``ets_printf``, so it is not accessible outside.)
To override default verbosity level at file or component scope, define ``LOG_LOCAL_LEVEL`` macro. At file scope, define it before including ``esp_log.h``, e.g.:
..code-block:: c
#define LOG_LOCAL_LEVEL ESP_LOG_VERBOSE
#include "esp_log.h"
At component scope, define it in component makefile:
By default logging library uses vprintf-like function to write formatted output to dedicated UART. With calling a simple API, all log output my be routed to JTAG instead, and make the logging several times faster. For details please refer to section :ref:`app_trace-logging-to-host`.
