Locking out Timer Interrupts

[David B Stewart]

How can timer interrupts which force context switches be locked out for a
short period?

I have some user code (not kernel code) which must run to completion (less
than 100 microseconds worth) before that process does a context switch
because of and expired time quantum.   Device drivers have the ability to
use the "splx" routine, but this code is not a device driver.  Is there
some kind of system call that will allow me to do that?

Alternately, can anyone give me a quick description on how to create my
own system calls "lock" and "unlock", using the 'syscall' command.  (or
point me to the proper location in the Sun Manuals; I could not find
anywhere which describes how to create your own system calls; the manual
only describes how to use them).

I am using SunOS 4.0.3, and I don't have the Sun source code.

Thanks.