Debugger on top of L4

good day

Im totally newbie to l4, but my aim is to develop source level debugger for our system built on top of L4. So the procedure for source level debugger is common and may be presented in following steps:

1) Cause undef exception from user task (using undef instruction) 2) Catch it by undef exception handler 3) Save CPU registers 4) Suspend running thread. Suspension must be performed by my code - not by l4 system code. 5) Continue execution with next scheduled thread

But untill now i have no ideas how to suspend thead by my self. I even cant find l4 code responsible for thread suspension.

Does anyone knows where can i find suspention procedure in l4 code? Probably someone has code snippets for such kind of actions?

thanks in advance