Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32H7x5_CM7/FDCAN1/FDCAN_TTTMK#0x0
FDCAN TT Time Mark Register
Time Mark
Time Mark Cycle Code
TT Time Mark Register Locked
https://github.com/cmsis-svd/cmsis-svd-data