I've made a small bootloader to allow W7500 update on a custom board without SWD or external probe. Sometimes, i have deadlock into IAP (never return from a call). I've made many tests, and finally try to re-write IAP and execute it into SRAM (to avoid delay into cpu fetch). Result is the same, CPU sometimes 'stop' when bit 16 of FACCR is set (0x00010000). During test, i've seen that when i reduce system frequency, i can drasticly reduce the number of errors (from 10% @ 20MHz to ~0% @ 8MHz) Is the Flash controller can work on the same frequency range than CPU ? Or, if there is a limit, what is the maximum frequency ?