[LinuxPPS] PPS kernel discipline

[Hal V. Engel]

On Wednesday 25 March 2009 08:54:57 am Udo van den Heuvel wrote:
> Thorsten Mühlfelder wrote:
> > When kernel PPS support is enabled, the PPS driver can direct the signal
> > directly to the kernel. Note that the PPS driver does not normally enable
> > the PPS kernel, since performance is generally better with older systems.
>
> So it is optional.
> Disabled by default.
> And without that stuff works(TM).
> So it is for improving even more.
>
> Is a VIA Ek8000 quick enough?

"This (meaning kernel discipline) is advised for newer machines in the Pentium 
class."  Pentium machines were originally only 100MHz hardware so any modern 
hardware, including any recent VIA hardware, is going to be WAY faster.

Kernel discipline has been talked about on the list before.  It is an optional 
part of the specification and is currently not part of LinuxPPS.  Right now I 
think the goal is to get the basic PPS stuff into the kernel and then to work 
at adding enhancements like kernel discipline. 

In addition to basic PPS support PPSKIT had kernel discipline along with 
nanokernel capabilities.  Unfortunately it never made it into the kernel.  
Perhaps because it was too ambitious.   Current kernels are now nanosecond 
capable and there is a possibility that basic PPS capabilities will be part of 
the kernel sometime soon since the LinuxPPS patches were considered for 
inclusion in 2.6.29 and there has been some work done to correct the issues 
that prevented inclusion.  Since it appears that this needs to be added to the 
kernel in small incremental steps perhaps the right thing to do would be to 
have a separate patch set for enabling kernel discipline so that work on 
getting basic PPS into the kernel can go forward unimpeded.

Hal