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Logging library

:link_to_translation:zh_CN:[中文]

Overview

The logging library provides three ways for setting log verbosity:

  • At compile time: in menuconfig, set the verbosity level using the option CONFIG_LOG_DEFAULT_LEVEL.
  • Optionally, also in menuconfig, set the maximum verbosity level using the option CONFIG_LOG_MAXIMUM_LEVEL. By default, this is the same as the default level, but it can be set higher in order to compile more optional logs into the firmware.
  • At runtime: all logs for verbosity levels lower than CONFIG_LOG_DEFAULT_LEVEL are enabled by default. The function :cppesp_log_level_set can be used to set a logging level on a per-module basis. Modules are identified by their tags, which are human-readable ASCII zero-terminated strings.
  • At runtime: if CONFIG_LOG_MASTER_LEVEL is enabled then a Master logging level can be set using :cppesp_log_set_level_master. This option adds an additional logging level check for all compiled logs. Note that this will increase application size. This feature is useful if you want to compile a lot of logs that are selectable at runtime, but also want to avoid the performance hit from looking up the tags and their log level when you don't want log output.

There are the following verbosity levels:

  • Error (lowest)
  • Warning
  • Info
  • Debug
  • Verbose (highest)

Note

The function :cppesp_log_level_set cannot set logging levels higher than specified by CONFIG_LOG_MAXIMUM_LEVEL. To increase log level for a specific file above this maximum at compile time, use the macro LOG_LOCAL_LEVEL (see the details below).

How to Use Logging Library

In each C file that uses logging functionality, define the TAG variable as shown below:

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 (lowest)
  • ESP_LOGW - Warning
  • ESP_LOGI - Info
  • ESP_LOGD - Debug
  • ESP_LOGV - Verbose (highest)

Additionally, there are ESP_EARLY_LOGx versions for each of these macros, e.g. :cESP_EARLY_LOGE. These versions have to be used explicitly in the early startup code only, before heap allocator and syscalls have been initialized. Normal ESP_LOGx macros can also be used while compiling the bootloader, but they will fall back to the same implementation as ESP_EARLY_LOGx macros.

There are also ESP_DRAM_LOGx versions for each of these macros, e.g. :cESP_DRAM_LOGE. These versions are used in some places where logging may occur with interrupts disabled or with flash cache inaccessible. Use of this macros should be as sparse as possible, as logging in these types of code should be avoided for performance reasons.

Note

Inside critical sections interrupts are disabled so it's only possible to use ESP_DRAM_LOGx (preferred) or ESP_EARLY_LOGx. Even though it's possible to log in these situations, it's better if your program can be structured not to require it.

To override default verbosity level at file or component scope, define the 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 the component CMakeLists:

target_compile_definitions(${COMPONENT_LIB} PUBLIC "-DLOG_LOCAL_LEVEL=ESP_LOG_VERBOSE")

To configure logging output per module at runtime, add calls to the function :cppesp_log_level_set as follows:

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

Note

The "DRAM" and "EARLY" log macro variants documented above do not support per module setting of log verbosity. These macros will always log at the "default" verbosity level, which can only be changed at runtime by calling esp_log_level("*", level).

Even when logs are disabled by using a tag name, they will still require a processing time of around 10.9 microseconds per entry.

Master Logging Level

To enable the Master logging level feature, the CONFIG_LOG_MASTER_LEVEL option must be enabled. It adds an additional level check for ESP_LOGx macros before calling :cppesp_log_write. This allows to set a higher CONFIG_LOG_MAXIMUM_LEVEL, but not inflict a performance hit during normal operation (only when directed). An application may set the master logging level (:cppesp_log_set_level_master) globally to enforce a maximum log level. ESP_LOGx macros above this level will be skipped immediately, rather than calling :cppesp_log_write and doing a tag lookup. It is recommended to only use this in an top-level application and not in shared components as this would override the global log level for any user using the component. By default, at startup, the Master logging level is CONFIG_LOG_DEFAULT_LEVEL.

Note that this feature increases application size because the additional check is added into all ESP_LOGx macros.

The snippet below shows how it works. Setting the Master logging level to ESP_LOG_NONE disables all logging globally. :cppesp_log_level_set does not currently affect logging. But after the Master logging level is released, the logs will be printed as set by :cppesp_log_level_set.

// Master logging level is CONFIG_LOG_DEFAULT_LEVEL at start up and = ESP_LOG_INFO
ESP_LOGI("lib_name", "Message for print");          // prints a INFO message
esp_log_level_set("lib_name", ESP_LOG_WARN);        // enables WARN logs from lib_name

esp_log_set_level_master(ESP_LOG_NONE);             // disables all logs globally. esp_log_level_set has no effect at the moment

ESP_LOGW("lib_name", "Message for print");          // no print, Master logging level blocks it
esp_log_level_set("lib_name", ESP_LOG_INFO);        // enable INFO logs from lib_name
ESP_LOGI("lib_name", "Message for print");          // no print, Master logging level blocks it

esp_log_set_level_master(ESP_LOG_INFO);             // enables all INFO logs globally

ESP_LOGI("lib_name", "Message for print");          // prints a INFO message

Logging to Host via JTAG

By default, the logging library uses the vprintf-like function to write formatted output to the dedicated UART. By calling a simple API, all log output may be routed to JTAG instead, making logging several times faster. For details, please refer to Section app_trace-logging-to-host.

Thread Safety

The log string is first written into a memory buffer and then sent to the UART for printing. Log calls are thread-safe, i.e., logs of different threads do not conflict with each other.

Application Example

The logging library is commonly used by most ESP-IDF components and examples. For demonstration of log functionality, check ESP-IDF's examples directory. The most relevant examples that deal with logging are the following:

  • system/ota
  • storage/sd_card
  • protocols/https_request

API Reference

inc/esp_log.inc