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.

• Run 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)
• Turn on PPS support: PPS kernel consumer support is the option that should have become visible after changing the timer settings. If not, save and reload make menuconfig.
• Enter 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 *** 

• Unordered List ItemSave 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