pub unsafe extern "C" fn get_free_heap_size() -> u32 {
    unsafe extern "C" {
        fn esp_wifi_free_internal_heap() -> usize;
    }
**************************************************************************
Name: esp_get_free_heap_size

Description:
Get free heap size by byte

Input Parameters:
None

Returned Value:
Free heap size

*************************************************************************
esp-wifi/src/wifi/os_adapter.rs