Log library has two ways of managing log verbosity: compile time, set via menuconfig; and runtime, using esp_log_level_set function.

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.

In each C file which uses logging functionality, define TAG variable like this:

static const char* TAG = "MyModule";

then use one of logging macros to produce output, e.g:

ESP_LOGW(TAG, "Baud rate error %.1f%%. Requested: %d baud, actual: %d baud", error * 100, baud_req, baud_real);

Several macros are available for different verbosity levels:

• ESP_LOGE - error
• ESP_LOGW - warning
• ESP_LOGI - info
• ESP_LOGD - debug
• ESP_LOGV - verbose

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.:

#define LOG_LOCAL_LEVEL ESP_LOG_VERBOSE
#include "esp_log.h"

At component scope, define it in component makefile:

CFLAGS += -D LOG_LOCAL_LEVEL=ESP_LOG_DEBUG

To configure logging output per module at runtime, add calls to esp_log_level_set function:

esp_log_level_set("*", ESP_LOG_ERROR);        // set all components to ERROR level
esp_log_level_set("wifi", ESP_LOG_WARN);      // enable WARN logs from WiFi stack
esp_log_level_set("dhcpc", ESP_LOG_INFO);     // enable INFO logs from DHCP client

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`.