A technology for controlling non-volatile memory with a multi-stage controller is shown. The multi-stage controller uses an upper on-chip interconnect and a lower on-chip interconnect and includes a serial peripheral bus (SPI) loader, a frond-end central processing unit (FE CPU), and an arbitrator. When being connected to the lower on-chip interconnect, the SPI loader performs code loading for the multi-stage controller. After the SPI loader finishes the code loading, the SPI loader is disconnected from the lower-stage on-chip bus, and the arbitrator connects the FE CPU to the lower on-chip interconnect. This way, the communication channel between the upper on-chip interconnect and the lower on-chip interconnect is not occupied by the FE CPU.