ALARM(2) System Calls Manual ALARM(2)
alarm - schedule signal after specified time
Alarm causes signal SIGALRM, see signal(2), to be sent to the invoking
process in a number of seconds given by the argument. Unless caught or
ignored, the signal terminates the process.
Alarm requests are not stacked; successive calls reset the alarm clock.
If the argument is 0, any alarm request is cancelled. Because the
clock has a 1-second resolution, the signal may occur up to one second
early; because of scheduling delays, resumption of execution of when
the signal is caught may be delayed an arbitrary amount. The longest
specifiable delay time is 65535 seconds.
The return value is the amount of time previously remaining in the
pause(2), signal(2), sleep(3)
(alarm = 27.)
(seconds in r0)
(previous amount in r0)