[seL4] using libmuslc library question

Hello, I have tried to call usleep() function from seL4 'main' thread and it crashes the system with error: Caught cap fault in send phase at address 0x0 while trying to handle: vm fault on code at address 0x200 with status 0x82000006 in thread 0xff807bfe2200 "rootserver" at address 0x200 With stack: How to use this library? Thank you, Leonid