Function esp_idf_sys::esp_log_timestamp

pub unsafe extern "C" fn esp_log_timestamp() -> u32

@brief Function which returns timestamp to be used in log output

This function is used in expansion of ESP_LOGx macros. In the 2nd stage bootloader, and at early application startup stage this function uses CPU cycle counter as time source. Later when FreeRTOS scheduler start running, it switches to FreeRTOS tick count.

For now, we ignore millisecond counter overflow.

@return timestamp, in milliseconds