one question about l4_thread_ex_regs flags

[Guanghui, Cheng]

Hello:
	About the l4_thread_ex_regs system call there are 2 flags related with 
exception ipc.  I only know the thread with these flags could generate the 
exception ipc but i don't know what is the difference between these flags: 
L4_THREAD_EX_REGS_RAISE_EXCEPTION , L4_THREAD_EX_REGS_ALIEN and 
L4_THREAD_EX_REGS_ALIEN | L4_THREAD_EX_REGS_ALIEN.

	So, i write a following program to test the behaviour with different flags :

void idle(void *data)
{
	l4_sleep(1000);
	l4_sleep(1000);
	l4_sleep(1000);
	l4_sleep(1000);
	l4_sleep(1000);
}
int main()
{
	...
	l4_threadid_t me = l4_myself();
	l4thread_create(idle, NULL, L4THREAD_CREATE_ASYNC);
	...
	l4_thread_ex_regs_flags(idle_thread,  ~0UL, ~0UL,
		&_preempter, &me,
 		&o, &o, &o,
		L4_THREAD_EX_REGS_RAISE_EXCEPTION
		| L4_THREAD_EX_REGS_ALIEN);
	while(1)
	{
		l4_ipc_wait(&src, ...);
		printf("thread :%d:%d\n", src.id.task, src.id.lthread);
	}
}

	I tried 3 combination about these 2 flags but the output is the same as this:

exceptio| thread :8:3

	i don't know why there is only one exception ipc. But the idle function 
includes 5 system calls.  Additionally, it seems the ALIEN state is 
TEMPORARILY. I set once there is one exception ipc, twice two exception ipc. 
Can you explain me?
	Thanks.
										Cheng Guanghui