#!/usr/bin/python3

# Watch PPS counter and write log file

# This runs on a Linux system.
# It needs something like:
#  ldattach 18 /dev/ttyS0
# which creates /dev/pps0 and friends

# It expects a 60 (50?) Hz signal to be connected to DCD.
# That's the normal PPS input pin for NTP.
# A 5 volt AC wall wart transformer works OK.
# Higher voltages may need a simple resistive voltage divider.


import os, time

daemon = 1

ppsname = "/sys/class/pps/pps1" + "/assert"

logRoot = "/var/log/pps/ppsstats"

logFile = ""
logName = ""
logDay = 0

MJD_1970 = 40587           # MJD for 1 Jan 1970

def GetLogFile(now):
  global logFile, logName, logDay
  day = int(now/86400)
  if logDay == day: return
  when = time.strftime("%Y%m%d", time.gmtime(now))
  logName = "%s.%s" % (logRoot, when)
  logFile = open(logName, "a")
  if logDay == 0:
    logFile.write("\n\n")
  logDay = day
  if os.path.exists(logRoot):
    os.unlink(logRoot)
  os.link(logName, logRoot)

def GetData():
  line = open(ppsname).read()
  hash = line.find("#")
  when = line[:hash]
  count = line[hash+1:-1]
  # print when, count, line
  return (float(when), int(count))

if (daemon):
  print("Daemonizing.  Bye.")
  import ctypes
  ctypes.cdll.LoadLibrary("libc.so.6")
  libc = ctypes.CDLL("libc.so.6", use_errno=True)
  xx = libc.daemon(0, 0)


(oldWhen, oldCount) = GetData()

while 1:
  time.sleep(10)
  (when, count) = GetData()
  deltaWhen = when - oldWhen
  deltaCount = count - oldCount

  now = time.time()
  day = int(now/86400)
  sec = now - day*86400
  mjday = day + MJD_1970
  GetLogFile(now)
  # Format mimics ntpd's log files
  logFile.write("%d %9.3f" % (mjday, sec))
  logFile.write("  %.6f %d %10.6f %4d\n" % (when, count, deltaWhen, deltaCount) )
  logFile.flush()
  oldWhen = when
  oldCount = count