watchdog3.py

#watchdog.py
""" Watchdog.py modified for python 3 compatibility.

This is a convenience function implementing a watchdog timer with indirect loop
control via inspection of provided PVs. This is used throughout the fstiming
codebase. This tool is not currently asynchronous.

Dependencies:
- pyepics
"""

import time  #includes sleep command to wait for other users
import epics

class watchdog():
    def __init__(self, pv):  # pv is an already connected pv
        self.pv = pv
        self.counter = 0;
        try:
            self.pv.get( timeout=1.0)
            self.value = self.pv.value
            if self.value < 0:#command to exit programs
                self.error = 1 #exit program
                print('watchdog pv negative - exiting')
                return
            print('initializing watchdog')
            time.sleep(1) # wait 1 second1 for an update
            self.pv.get(timeout=1.0)
        except:
            print('cant write watchdog pv, exiting')
            self.error = 1
            return
        if self.pv.value < 0:#command to exit programs
            self.error = 1 #exit program
            print('watchdog pv negative - exiting')
            return
        if self.pv.value != self.value:
            self.error = 1
            print('another program is incrementing the watchdog')
            return
        self.error = 0  # OK to continue

    def check(self):  # check watchdog timer
        try:
            self.pv.get(timeout=1.0)
        except:
            print('not able to read watchdog PV, continuing to try')
            self.error = 0  # not an error (at least for now)
            return
        if self.pv.value < 0:
            self.error = 1 #exit program
            print('watchdog pv negative - exiting')
            return
        if self.pv.value != self.value:  # value changed
            self.error = 1
            print('another program is incrementing the watchdog')
            return
        self.error = 0
        self.value = self.pv.value+1
        self.pv.put(value = self.value, timeout=1.0) # write new number to increment