lvgl/docs/porting/log.md

# 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(lv_log_level_t level, 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.