pps_linux.go

// +build linux

package main

import (
	"flag"
	"log"
	"os"
	"time"
	"unsafe"

	"golang.org/x/sys/unix"
)

func setupPPS() {
	f, err := os.OpenFile(*ppsPath, os.O_RDWR, 0)
	if err != nil {
		log.Fatalf("Unable to open pps device %#v", err)
	}

	FD := f.Fd()
	a := int(FD)
	ppsFD = &a
	ppsFile = f

	PP := unix.PPSKParams{}
	unix.Syscall(unix.SYS_IOCTL, uintptr(*ppsFD), uintptr(unix.PPS_GETPARAMS), uintptr(unsafe.Pointer(&PP)))
	if *ppsDebug {
		log.Printf("PPS Cap: %#v", PP)
	}
	PP.Mode = 0x01  // PPS_CAPTUREASSERT
	PP.Mode |= 0x10 // PPS_OFFSETASSERT
	PP.Assert_off_tu.Nsec = 0
	PP.Assert_off_tu.Sec = 0
	_, _, err2 := unix.Syscall(unix.SYS_IOCTL, uintptr(*ppsFD), uintptr(unix.PPS_SETPARAMS), uintptr(unsafe.Pointer(&PP)))
	if *ppsDebug {
		log.Printf("PPS Set Cap: %#v", PP)
	}
	if err2 != 0 {
		log.Fatalf("Failed to setup pps device %v", err)
	}
}

var ppsFD *int
var ppsFile *os.File // To stop GC
var ppsDebug = flag.Bool("pps.debug", false, "Enable debug output for PPS inputs")

func waitForPPSPulse() time.Time {
	if ppsFD == nil {
		setupPPS()
	}

	a := unix.PPSFData{}
	a.Timeout.Sec = 3
	_, _, err := unix.Syscall(unix.SYS_IOCTL, uintptr(*ppsFD), uintptr(unix.PPS_FETCH), uintptr(unsafe.Pointer(&a)))
	if err != 0 {
		log.Printf("PPS Pulse failed! %v / FD %v", err, *ppsFD)
	}
	if *ppsDebug {
		log.Printf("%#v", a)
	}
	return time.Unix(a.Info.Assert_tu.Sec, int64(a.Info.Assert_tu.Nsec))
}