>         I downloaded the clock.c from
> ftp://ftp.netbsd.org/pub/NetBSD-current/sys/i386/isa/clock.c
> and compile it, I get the error:- "pcppi.h not found", I check
> the clock.c code and there is a include header file #include
> "pcppi.h"
>
>         I downloaded the ls-lRA.gz from ftp.netbsd.org, gunzip
> it and I also can not find where is the location of pcppi.h

It's a generated header, generated by config on newer systems.
My corresponding header contains the following:

vader# cat /usr/src/sys/arch/i386/compile/SWAP/pcppi.h
#define NPCPPI  1
vader#

Apparently it has something to do with the PC speaker beeps.
There's probably just two values to try: 0 and 1, and I think in
your case I'd try 0 first, since the main objective is not to get
the PC to say "beep" but to test whether the clock is working
correctly in this particular corner case.

- H=E5vard