Re: nanosleep question

[george anzinger <george@mvista.com>]

Michael Reinelt wrote:
> 
> george anzinger wrote:
> >
> > Michael Reinelt wrote:
> > >
> > > At the moment I implemented by own delay loop using a small assembler
> > > loop similar to the one used in the kernel. This has two disadvantages:
> > > assembler isn't that portable, and the loop has to be calibrated.
> >
> > Why not use C?  As long as you calibrate it, it should do just fine.
> Because the compiler might optimize it away.

Not if you use volatile on the data type.
> 
> > On
> > the other hand, since you are looping anyway, why not loop on a system
> > time of day call and have the loop exit when you have the required time
> > in hand.  These calls have microsecond resolution.
> I'm afraid they don't (at least with kernel 2.0, I didn't try this with
> 2.4). 

Gosh, I started with 2.2.14 and it does full microsecond resolution.

They have microsecond resolution, but increment only every 1/HZ.
> 
> Someone gave me a hint to loop on rdtsc. I will look into this.

This ticks at 1/"cpu MHz", which can be found by: "cat /proc/cpuinfo"
> 
> > > - why are small delays only possible up to 2 msec? what if I needed a
> > > delay of say 5msec? I can't get it?
> >
> > If you want other times, you can always make more than one call to
> > nanosleep.
> Good point!

~snip~

George