The user manual states (UM10912 rev 2.4, page 126):
8 system clocks flash access time (for system clock rates up to 168 MHz and for system clock rates 180 MHz < CCLK <= 220 MHz).
9 system clocks flash access time (for system clock rates up to 180 MHz).
At 220 MHz the system clock/access time can be lower when compared to 180 MHz because the power library optimizes the on-chip voltage regulator.
Running with 9 cycles at 220 MHz works without issues, but when decreasing to 8 cycles I have problems with occasional garbage data when reading from flash resulting in hard-to-debug crashes. I've tried both using a 25 MHz external oscillator and the FRO 12 Mhz and the issue remains. I'm using the MCUxpresso config tool to generate the clock setup code.
