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lvgl_v8_back/lvgl/docs/porting/log.md

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+# Logging
+
+LVGL has a built-in *Log* module to inform the user about what is happening in the library.
+
+## Log level
+To enable logging, set `LV_USE_LOG  1` in `lv_conf.h` and set `LV_LOG_LEVEL` to one of the following values:
+- `LV_LOG_LEVEL_TRACE` A lot of logs to give detailed information
+- `LV_LOG_LEVEL_INFO`  Log important events
+- `LV_LOG_LEVEL_WARN`  Log if something unwanted happened but didn't cause a problem
+- `LV_LOG_LEVEL_ERROR` Only critical issues, where the system may fail
+- `LV_LOG_LEVEL_USER` Only user messages
+- `LV_LOG_LEVEL_NONE`  Do not log anything
+
+The events which have a higher level than the set log level will be logged too. E.g. if you `LV_LOG_LEVEL_WARN`, errors will be also logged.
+
+## Printing logs
+
+### Logging with printf
+If your system supports `printf`, you just need to enable `LV_LOG_PRINTF` in `lv_conf.h` to send the logs with `printf`.
+
+
+### Custom log function
+If you can't use `printf` or want to use a custom function to log, you can register a "logger" callback with `lv_log_register_print_cb()`.
+
+For example:
+
+```c
+void my_log_cb(const char * buf)
+{
+  serial_send(buf, strlen(buf));
+}
+
+...
+
+
+lv_log_register_print_cb(my_log_cb);
+
+```
+
+## Add logs
+
+You can also use the log module via the `LV_LOG_TRACE/INFO/WARN/ERROR/USER(text)` or `LV_LOG(text)` functions. Here:
+
+-  `LV_LOG_TRACE/INFO/WARN/ERROR/USER(text)` append following information to your `text`
+  - Log Level
+  - \_\_FILE\_\_
+  - \_\_LINE\_\_
+  - \_\_func\_\_
+- `LV_LOG(text)` is similar to `LV_LOG_USER` but has no extra information attached.