clock.h

[Peter Pentchev]

On Mon, Feb 28, 2005 at 11:39:52PM +0800, Kathy Quinlan wrote:
> I have this:
> 
> #include <machine/clock.h>
> 
> In program I use this:
> 
> DELAY(1000);
> 
> I get this:
> 
> undefined referance to 'DELAY'
> 
> when I compile the program with GCC with flags -Wall -g -o com main.c
> 
> ANY ideas ??
> 
> I have looked in the relevent header and it seems to be there

Yes, it is in clock.h, but...

/*-
 * Kernel interface to machine-dependent clock driver.

That's the way that clock.h starts.  The 'kernel interface' part means
that this is a header file that declares functions that are used *only*
within the FreeBSD kernel - since they are only implemented in another
part of the kernel code.  You cannot use these definitions and functions
from a userland program, as you are trying to do.

The reason that the DELAY() declaration seems to be in the header file,
yet the compiler does not see it, is the #ifdef _KERNEL at the top of
clock.h :)  This is just a level of protection that accomplishes exactly
that - no userland program should *ever* define the _KERNEL symbol, so
no userland program will be fooled into believing that there is a
DELAY() function that it could possibly use.  It simply cannot, since
the DELAY() function is declared within kernel code for use by the
kernel only.

If you want a high-precision delay/sleep interface in a userland
program, take a look at the usleep(2) and nanosleep(2) syscalls.

G'luck,
Peter

-- 
Peter Pentchev	roam at ringlet.net    roam at cnsys.bg    roam at FreeBSD.org
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