[LinuxPPS] LinuxPPS for Raspberry Pi?

[tlhackque]

I've just acquired a Raspberry Pi (RPI), and have attached a Garmin 
GPS18x-LVC (FW 3.80) to the serial port and the PPS output to GPIO4 (via 
an inverting level converter).  It's a nice package, except for not 
having a local clock).

I have successfully configured ntpd (4.2.6p5) to see it as a NEMA clock 
(right now it's noselect while I measure the serial data offset).

      remote           refid      st t when poll reach   delay offset  
jitter
==============================================================================
  127.127.20.1    .GPS.            0 l   55   64  377    0.000 -682.66   
5.112

For the next step, PPS - some questions:

1. Has anyone tread this road already?  I've seen several 
inquiries/aborted attempts on the web, but no successes.

2. The RPI kernel is Debian based.  It has sysfs gpio support 
(/sys/class/gpio), and from the shell, I can see the pin toggling if I 
export the pin.

      How do I tell if the kernel has PPS support compiled-in?

3. Do I need compiled-in kernel support, or can PPS just be modprobed 
in?  (It looks like compiling the kernel on RPI is a major undertaking  
- http://elinux.org/RPi_Kernel_Compilation.)  If the latter, how do I 
build the modules?

4. What's the minimal support that we could try to get the RPI 
developers to include in the distributed kernel to enable PPS, or at 
least make it less of a project to build?

I'd have to native (on the RPI) build anything for this project ('disk' 
is a 16GB SD flash card), so any help would be appreciated.

Thanks.

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