FLASH option status register
| OPT_BUSY | Option byte change ongoing flag |
| BOR_LEV | Brownout level option status bit |
| IWDG1_SW | IWDG1 control option status bit |
| NRST_STOP_D1 | D1 DStop entry reset option status bit |
| NRST_STBY_D1 | D1 DStandby entry reset option status bit |
| RDP | Readout protection level option status byte |
| IWDG_FZ_STOP | IWDG Stop mode freeze option status bit |
| IWDG_FZ_SDBY | IWDG Standby mode freeze option status bit |
| ST_RAM_SIZE | DTCM RAM size option status |
| SECURITY | Security enable option status bit |
| IO_HSLV | I/O high-speed at low-voltage status bit (PRODUCT_BELOW_25V) |
| OPTCHANGEERR | Option byte change error flag |