T-DeckLoader/lib/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:

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.