README.rst
1Logging library
2===============
3
4Overview
5--------
6
7The logging library provides two ways for setting log verbosity:
8
9- **At compile time**: in menuconfig, set the verbosity level using the option :ref:`CONFIG_LOG_DEFAULT_LEVEL`.
10- Optionally, also in menuconfig, set the maximum verbosity level using the option :ref:`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 otional logs into the firmware.
11- **At runtime**: all logs for verbosity levels lower than :ref:`CONFIG_LOG_DEFAULT_LEVEL` are enabled by default. The function :cpp:func:`esp_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.
12
13There are the following verbosity levels:
14
15- Error (lowest)
16- Warning
17- Info
18- Debug
19- Verbose (highest)
20
21.. note::
22
23 The function :cpp:func:`esp_log_level_set` cannot set logging levels higher than specified by :ref:`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).
24
25
26How to use this library
27-----------------------
28
29In each C file that uses logging functionality, define the TAG variable as shown below:
30
31.. code-block:: c
32
33 static const char* TAG = "MyModule";
34
35Then use one of logging macros to produce output, e.g:
36
37.. code-block:: c
38
39 ESP_LOGW(TAG, "Baud rate error %.1f%%. Requested: %d baud, actual: %d baud", error * 100, baud_req, baud_real);
40
41Several macros are available for different verbosity levels:
42
43* ``ESP_LOGE`` - error (lowest)
44* ``ESP_LOGW`` - warning
45* ``ESP_LOGI`` - info
46* ``ESP_LOGD`` - debug
47* ``ESP_LOGV`` - verbose (highest)
48
49Additionally, there are ``ESP_EARLY_LOGx`` versions for each of these macros, e.g. :c:macro:`ESP_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.
50
51There are also ``ESP_DRAM_LOGx`` versions for each of these macros, e.g. :c:macro:`ESP_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 sparing as possible, as logging in these types of code should be avoided for performance reasons.
52
53.. note::
54
55 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.
56
57To override default verbosity level at file or component scope, define the ``LOG_LOCAL_LEVEL`` macro.
58
59At file scope, define it before including ``esp_log.h``, e.g.:
60
61.. code-block:: c
62
63 #define LOG_LOCAL_LEVEL ESP_LOG_VERBOSE
64 #include "esp_log.h"
65
66At component scope, define it in the component makefile:
67
68.. code-block:: cmake
69
70 target_compile_definitions(${COMPONENT_LIB} PUBLIC "-DLOG_LOCAL_LEVEL=ESP_LOG_VERBOSE")
71
72To configure logging output per module at runtime, add calls to the function :cpp:func:`esp_log_level_set` as follows:
73
74.. code-block:: c
75
76 esp_log_level_set("*", ESP_LOG_ERROR); // set all components to ERROR level
77 esp_log_level_set("wifi", ESP_LOG_WARN); // enable WARN logs from WiFi stack
78 esp_log_level_set("dhcpc", ESP_LOG_INFO); // enable INFO logs from DHCP client
79
80.. note::
81
82 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)``.
83
84Logging to Host via JTAG
85^^^^^^^^^^^^^^^^^^^^^^^^
86
87By 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 :ref:`app_trace-logging-to-host`.
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