Logging

LVGL has a built-in Logging module to inform the user about what is happening in the library.

LVGL has a built-in Logging module to inform the user about what is happening in the library.

Configuring Logging

Log Level

To enable logging, set LV_USE_LOG in lv_conf.h to a non-zero value and set LV_LOG_LEVEL to one of the following values. They are prioritized as follows (from most to least verbose):

• 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: Log only critical issues, where the system may fail.
• LV_LOG_LEVEL_USER: Log only custom log messages added by the user.
• LV_LOG_LEVEL_NONE: Do not log anything.

When you set LV_LOG_LEVEL to a certain level, only messages with that level or higher priority (less verbose) will be logged.

Example: you set LV_LOG_LEVEL to LV_LOG_LEVEL_WARN, then LV_LOG_LEVEL_WARN, LV_LOG_LEVEL_ERROR and LV_LOG_LEVEL_USER messages will be logged.

Log Output

If your system supports printf, you just need to enable LV_LOG_PRINTF in lv_conf.h to output log messages with printf.

If you can't use printf or want to use a custom function to log, you can register a "logging" function with lv_log_register_print_cb.

For example:

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);

Using Logging

You use the log module via the following macros:

• LV_LOG_TRACE(text)
• LV_LOG_INFO(text)
• LV_LOG_WARN(text)
• LV_LOG_ERROR(text)
• LV_LOG_USER(text)
• LV_LOG(text)

The first 5 macros append the following information to your text:

• Log Level name ("Trace", "Info", "Warn", "Error", "User")
• __FILE__
• __LINE__
• __func__

LV_LOG(text) is similar to LV_LOG_USER but has no extra information added.

API