Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f2/STM32F215/Ethernet_PTP/PTPTSLR#0x0
Ethernet PTP time stamp low register
System time subseconds
System time positive or negative sign
https://github.com/modm-io/cmsis-svd-stm32