Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f2/STM32F217/FLASH/ACR#0x0
Flash access control register
Latency
Prefetch enable
Instruction cache enable
Data cache enable
Instruction cache reset
Data cache reset
https://github.com/modm-io/cmsis-svd-stm32