Enable PPS support in Raspian

DUNE has a task called Supervisors.ClockPPS that is used to dicipline the clock from both IMC::GpsFix messages and a PPS source. To get this to work, the kernel has to be compiled with two options not currently enabled by default:

• CONFIG_PPS (“PPS support” in “make menuconfig”)
• CONFIG_NTP_PPS (“PPS kernel consumer support” in “make menuconfig”)

mkdir ppskernel
cd ppskernel
git clone https://github.com/raspberrypi/linux.git
cd linux
make mrproper
zcat /proc/config.gz > .config
make oldconfig

Then comes the hard part, setting the options. Normally this is straight forward, but due to some options only showing when others are disabled, it may be a little tricky.

make menuconfig

Go to General setup ---> Timers subsystem ---> and disable Old Idle dynticks config, then enter Timer tick handling and change it to Periodic timer ticks (constant rate, no dynticks)

PPS kernel consumer support is the option that should have become visible after changing the timer settings. If not, save and reload make menuconfig.

  Device Drivers ---> PPS support --->
          <M> PPS support  
          [ ]    PPS debugging messages
          [*]    PPS kernel consumer support   
                 *** PPS clients support ***         
          < >    Kernel timer client (Testing client, use for debug)
          <M>    PPS line discipline
          <M>    PPS client using GPIO
                 *** PPS generators support *** 

Save and exit. To verify, check the .config file that has been created in the same folder (nano .config). These options should be present somewhere in the file:

CONFIG_PPS=y
CONFIG_NTP_PPS=y
#
# Timers subsystem
#
CONFIG_TICK_ONESHOT=y
CONFIG_HZ_PERIODIC=y
# CONFIG_NO_HZ_IDLE is not set
# CONFIG_NO_HZ_FULL is not set
# CONFIG_NO_HZ is not set
CONFIG_HIGH_RES_TIMERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

• How to PPS on Raspberry Pi