Hi @Amily,
Adding to what Marek mentioned, the following knowledge base article is a good starting point for understanding how the i.MX RT boots from FlexSPI.
i.MX RT FLEXSPI booting guide
Additionally, could you help me with the following questions?
When you performed the test, did you use the EVK, or are you using a custom board?
If you are using a custom board, which flash device are you using? Is it the same device used on the EVK?
Which IDE are you using?
Which SDK version did you use?
When debugging the peripherals, did you use any SDK examples?
Best Regards,
Pablo