====== Atomic Pi ======
===== pps-gpio =====

  * https://www.kernel.org/doc/Documentation/devicetree/bindings/pps/pps-gpio.txt
  * https://github.com/digitalloggers/linux-custom-gpio-patches

PPS on GPIO1, LED on GPIO5

<code>
/dts-v1/;
/plugin/;

/ {
  fragment@0 {
    target-path="/";
    __overlay__ {
      pps: pps {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_pps>;
        gpios = <&gpiochip_stub_332 18 0>;
        assert-falling-edge;

        echo-gpios = <&gpiochip_stub_330 16 0>;
        echo-active-ms = <100>;

        compatible = "pps-gpio";
      };
    };
  };
};
</code>

build with:

<code>
dtc -I dts -O dtb -o /home/john/ppsgpio.dtb /home/john/pps-gpio.dts
</code>

kernel config options to add

<code>
CONFIG_OF=y
CONFIG_OF_DYNAMIC=y
CONFIG_OF_OVERLAY=y
CONFIG_OF_FLATTREE=y
CONFIG_OF_CONFIGFS=y
CONFIG_OF_GPIO_STUB=y
CONFIG_OF_ROOT_STUB=y
CONFIG_PPS=y
CONFIG_PPS_CLIENT_LDISC=y
CONFIG_PPS_CLIENT_GPIO=y
CONFIG_GPIO_SYSFS=y
</code>