[seL4] Does seL4 support periodic thread

Hi everyone,I have some questions about seL4's timer. I know seL4 is controlling the timer device. In the current release version, scheduling is tick-based, there's a periodic interrupt that feeds into the scheduler. I wanna know if seL4 support periodic thread. I want to implement a periodic process in Refos which is above seL4 kernel.And, if seL4 does not support periodic thread, could I modify the kernel scheduler? Does it influences formal verification? I find that Refos modifies _thread_state_​t enumeration-type variables (kernel\include\object\structures.h ). Does it influences formal verification? Thank you so much!!