******* Description ***********
ICACHE_PRELOAD_ENA | The bit is used to enable preload operation. It will be cleared by hardware after preload operation done. |
ICACHE_PRELOAD_DONE | The bit is used to indicate preload operation is finished. |
ICACHE_PRELOAD_ORDER | The bit is used to configure the direction of preload operation. 1: descending, 0: ascending. |