PyVisa.py

#    "$Name:  $";
#    "$Header:  $";
#=============================================================================
#
# file : PyVisa.py
#
# description : Python source for the PyVisa and its commands. 
#               The class is derived from Device. It represents the
#               CORBA servant object which will be accessed from the
#               network. All commands which can be executed on the
#               PyVisa are implemented in this file.
#
# project : TANGO Device Server
#
# Author: gcuni (main developer)
#         sblanch (threading, TODO split the thread to a class apart)
#
# $Revision: $
#
# $Log: $
#
# copyleft: Cells / Alba Synchrotron
#           Cerdanyola/Bellaterra
#           Spain
#
#=============================================================================
#          This file is generated by POGO
#    (Program Obviously used to Generate tango Object)
#
#         (c) - Software Engineering Group - ESRF
#=============================================================================
#

import PyTango

import sys

import array

## Needed PyVisa library from http://pyvisa.sourceforge.net/
from visa import *
from pyvisa import *

import threading

def cutlongstrings(string, length):
    """
    Cuts a given string with the given length
    @param string to be cutted
    @param length to be used
    @return the reduced string
    """
    return len(string)<length and string or "%s...(+%s)"%(string[:length],len(string)-length)

#==================================================================
#   PyVisa Class Description:
#
#         This class wraps the PyVisa python package from
#         http://pyvisa.sourceforge.net/
#         so it can be used as a device server for GPIB / Serial / Ethernet / ... devices
#
#==================================================================
#     Device States Description:
#
#   DevState.ON :     Device is Open (By default)
#   DevState.FAULT :  The device is in some fault state
#   DevState.OFF :    The device is OFF.
#==================================================================


class PyVisa(PyTango.Device_4Impl):
    """
    This class wraps the python PyVisa pacakge from
    http://pyvisa.sourceforge.net/
    so it can be used as a Device Server for GPIB/Serial/Ethernet devices
    """

    #--------- Add you global variables here --------------------------
    ## The instrument to talk with
    __instrument = None
    ## The different formats
    FORMATS = ["ASCII", "SINGLE", "", "DOUBLE", "BIG_ENDIAN"]

    def startThread(self, time=1):
        """
        Start the thread in 'daemon' mode.
        The target of the thread is the connect method which will try
        to keep the device server connected to the device.
        @param time to wait (paramkey that defaults to 1)
        """
        self.setReconnectTimeWait(time)
        if hasattr(self, '__thread') and self.__thread and self.__thread.isAlive():
            self.debug_stream("In %s::startTherad(): Trying to start threading when is already started."%self.get_name())
            return
        self.__threaded = True
        ## The communication between threads
        self.__joiner = threading.Event()
        self.__joiner.clear()
        self.__connectionEvent = threading.Event()#set when communications fails
        self.__connectionEvent.clear()
        self.__thread = threading.Thread(target=self.connect)
        self.__thread.setDaemon(True)
        self.__thread.start()
        self.__joiner.wait(0.1)

    def stopThread(self):
        """ It stops the thread. """
        if hasattr(self, '__joiner'):
            self.__joiner.set()
        if hasattr(self, '__connectionEvent'):
            self.__connectionEvent.set()
        if hasattr(self, '__thread'):
            self.__thread.join()

    def connect(self):
        """
        Main method of the thread.
        This method will check the connection with the device and
        set the state to ON or FAULT accordingly.
        """
        repeatMsgCnt = 0
        repeatMsg = ""
        while not self.__joiner.isSet():
            try:
                self.set_state(PyTango.DevState.INIT)
                #1: connect to the instrument
                # self.__instrument = instrument(self.VisaName) old visa format
                rm = ResourceManager(self.VisaLibrary)
                self.__instrument = rm.open_resource(self.VisaName)

                #2: setup the state
                self.set_state(PyTango.DevState.ON)
                self.machineStatus()
                #3: passive sleep until a connection requires the action of this thread
                self.debug_stream("In %s::connect(): Connectivity thread go to sleep"%(self.get_name()))
                self.__connectionEvent.wait()
                self.debug_stream("In %s::connect(): Connectivity thread wake up"%(self.get_name()))
                self.__connectionEvent.clear()
            except Exception as e:
                self.set_state(PyTango.DevState.FAULT)
                self.machineStatus(e)
                msg = "In %s::connect(): (re)connection thread exception: %s"%(self.get_name(),e)
                if repeatMsg == msg and not repeatMsgCnt == sys.maxsize:
                    repeatMsgCnt += 1
                else:
                    if not repeatMsgCnt == 0:#not necessary to say it is more than sys.maxint
                        self.error_stream("In %s::connect(): last message repeated %d times"%(self.get_name(),repeatMsgCnt))
                    self.error_stream(msg)
                    repeatMsg = msg
                    repeatMsgCnt = 0
                self.__connectionEvent.wait(self.getReconnectTimeWait())
        #out the loop means the thread has to finish and join the main one.
        self.debug_stream("In %s::connect(): thread exiting"%self.get_name())

    def getReconnectTimeWait(self):
        return self.__reconnectTimeWait

    def setReconnectTimeWait(self, time):
        self.__reconnectTimeWait = time


    def machineStatus(self,e=None):
        bar = "The device is in %s state."%(self.get_state())
        if not e == None:
            bar += "\n"+str(e)
        self.set_status(bar)


#------------------------------------------------------------------
#    Device constructor
#------------------------------------------------------------------
    def __init__(self, cl, name):
        PyTango.Device_4Impl.__init__(self, cl, name)
        PyVisa.init_device(self)
        self.__instrument = None

#------------------------------------------------------------------
#    Device destructor
#------------------------------------------------------------------
    def delete_device(self):
        #print "[Device delete_device method] for device", self.get_name()
        self.stopThread()
        self.__instrument = None
        self.timeout_set = False


#------------------------------------------------------------------
#    Device initialization
#------------------------------------------------------------------
    def init_device(self):
        """
        At the init stage the state is ON and a thred will be
        started in order to check periodically the state of the device.
        """
        self.debug_stream("In " + self.get_name() + "::init_device()")
        self.set_state(PyTango.DevState.ON)
        self.machineStatus()
        self.get_device_properties(self.get_device_class())
        #print "All properties set, creating the device "+self.VisaName
        try:
            #TODO: Not a try, a thread how allows connection in background
            self.startThread(1)
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            return

#------------------------------------------------------------------
#    Always excuted hook method
#------------------------------------------------------------------
    def always_executed_hook(self):
        self.debug_stream("In " + self.get_name() + "::always_excuted_hook()")

#==================================================================
#
#    PyVisa read/write attribute methods
#
#==================================================================
#------------------------------------------------------------------
#    Read Attribute Hardware
#------------------------------------------------------------------
    def read_attr_hardware(self, data):
        self.debug_stream("In " + self.get_name() + "::read_attr_hardware()")



#------------------------------------------------------------------
#    Read Timeout attribute
#------------------------------------------------------------------
    def read_Timeout(self, attr):
        self.debug_stream("In " + self.get_name() + "::read_Timeout()")
        
        #    Add your own code here
        try:
            attr_Timeout_read = self.__instrument.timeout
            attr.set_value(attr_Timeout_read)
        except Exception as e:
            self.error_stream("In ", self.get_name(), "::read_Timeout() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write Timeout attribute
#------------------------------------------------------------------
    def write_Timeout(self, attr):
        self.debug_stream("In " + self.get_name() + "::write_Timeout()")
        data=[]
        attr.get_write_value(data)
        self.warn_stream("%s: Timeout attribute value = %s"%(self.VisaName,data))

        #    Add your own code here
        try:
            timeout = data[0]
            if timeout == 0:
                timeout = 0.1
            self.__instrument.timeout = timeout
        except Exception as e:
            self.error_stream("In %s::write_Timeout() Exception: %s"%(self.get_name(),e))
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()
            return


#------------------------------------------------------------------
#    Read ChunkSize attribute
#------------------------------------------------------------------
    def read_ChunkSize(self, attr):
        self.debug_stream("In " + self.get_name() + "::read_ChunkSize()")
        
        #    Add your own code here

        try:
            attr_ChunkSize_read = self.__instrument.chunk_size
            attr.set_value(attr_ChunkSize_read)
        except Exception as e:
            self.error_stream("In ", self.get_name(), "::read_ChunkSize() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write ChunkSize attribute
#------------------------------------------------------------------
    def write_ChunkSize(self, attr):
        self.debug_stream("In " + self.get_name() + "::write_ChunkSize()")
        data=[]
        attr.get_write_value(data)
        #print self.VisaName+": ChunkSize attribute value = ", data

        #    Add your own code here
        try:
            self.__instrument.chunk_size = data[0]
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::write_ChunkSize() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Read ValuesFormat attribute
#------------------------------------------------------------------
    def read_ValuesFormat(self, attr):
        self.debug_stream( "In " + self.get_name() + "::read_ValuesFormat()")
        
        #    Add your own code here
        try:
            index = self.__instrument.values_format
            attr_ValuesFormat_read = self.FORMATS[index]
            attr.set_value(attr_ValuesFormat_read)
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::read_ValuesFormat() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write ValuesFormat attribute
#------------------------------------------------------------------
    def write_ValuesFormat(self, attr):
        self.debug_stream( "In " + self.get_name() + "::write_ValuesFormat()")
        data=[]
        attr.get_write_value(data)
        #self.debug_stream(self.VisaName+": ValuesFormat attribute value = ", data)

        #    Add your own code here
        try:
            format = data[0]
            self.__instrument.values_format = self.FORMATS.index(format)
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::write_ValuesFormat() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Read TermChars attribute
#------------------------------------------------------------------
    def read_TermChars(self, attr):
        self.debug_stream( "In " + self.get_name() + "::read_TermChars()")
        
        #    Add your own code here
        
        try:
            chars = self.__instrument.term_chars
            if chars == None:
                raise Exception("TermChars not defined")
            chars = chars.replace("\r", "CR")
            chars = chars.replace("\n", "LF")
            attr_TermChars_read = chars
            attr.set_value(attr_TermChars_read)
        except Exception as e:
            self.error_stream( "In %s::read_TermChars() Exception: %s"%(self.get_name(),e))
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write TermChars attribute
#------------------------------------------------------------------
    def write_TermChars(self, attr):
        self.debug_stream("In " + self.get_name() + "::write_TermChars()")
        data=[]
        attr.get_write_value(data)
        #self.debug_stream(self.VisaName+": TermChars attribute value = ", data)

        #    Add your own code here
        try:
            chars = data[0]
            chars = chars.replace("CR", "\r")
            chars = chars.replace("LF", "\n")
            self.__instrument.term_chars = chars
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::write_TermChars() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Read SendEnd attribute
#------------------------------------------------------------------
    def read_SendEnd(self, attr):
        self.debug_stream("In " + self.get_name() + "::read_SendEnd()")
        
        #    Add your own code here
        
        try:
            attr_SendEnd_read = self.__instrument.send_end
            attr.set_value(attr_SendEnd_read)
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::read_SendEnd() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write SendEnd attribute
#------------------------------------------------------------------
    def write_SendEnd(self, attr):
        self.debug_stream("In " + self.get_name() + "::write_SendEnd()")
        data=[]
        attr.get_write_value(data)
        #print self.VisaName+": SendEnd attribute value = ", data

        #    Add your own code here
        try:
            self.__instrument.send_end = data[0]
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::write_SendEnd() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Read Delay attribute
#------------------------------------------------------------------
    def read_Delay(self, attr):
        self.debug_stream("In " + self.get_name() + "::read_Delay()")
        
        #    Add your own code here
        
        try:
            attr_Delay_read = self.__instrument.delay
            attr.set_value(attr_Delay_read)
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::read_Delay() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#------------------------------------------------------------------
#    Write Delay attribute
#------------------------------------------------------------------
    def write_Delay(self, attr):
        self.debug_stream( "In " + self.get_name() + "::write_Delay()")
        data=[]
        attr.get_write_value(data)
        #print self.VisaName+": Delay attribute value = ", data

        #    Add your own code here
        try:
            self.__instrument.delay = data[0]
        except Exception as e:
            self.error_stream( "In ", self.get_name(), "::write_Delay() Exception: %s"%e)
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()



#==================================================================
#
#    PyVisa command methods
#
#==================================================================

#------------------------------------------------------------------
#    Open command:
#
#    Description: Open the VISA device
#                
#------------------------------------------------------------------
    def Open(self):
        self.debug_stream( "In " + self.get_name() + "::Open()")
        #    Add your own code here
        #if self.__instrument == None:
        #    self.__instrument = instrument(self.VisaName)
        #    self.set_state(PyTango.DevState.ON)
        self.startThread(1)


#---- Open command State Machine -----------------
    def is_Open_allowed(self):
        if self.get_state() in [PyTango.DevState.ON,
                                PyTango.DevState.FAULT]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Close command:
#
#    Description: Close the VISA device
#                
#------------------------------------------------------------------
    def Close(self):
        self.debug_stream( "In " + self.get_name() + "::Close()")
        #    Add your own code here
        try:
            self.__instrument.close()
            self.stopThread()
            self.set_state(PyTango.DevState.OFF)
            self.machineStatus()
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- Close command State Machine -----------------
    def is_Close_allowed(self):
        if self.get_state() in [PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Write command:
#
#    Description: Write a string to the VISA device
#                
#    argin:  DevVarCharArray    Command string
#------------------------------------------------------------------
    def Write(self, argin):
        self.debug_stream( "In " + self.get_name() + "::Write()")
        #    Add your own code here
        try:
            command = array.array('B', argin).tostring()
            #print self.VisaName+": Writing "+command
            self.__instrument.write(command)
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- Write command State Machine -----------------
    def is_Write_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Read command:
#
#    Description: Read the given amount of characters.
#                
#    argin:  DevUShort    Characters to read
#    argout: DevVarCharArray    Characters readed
#------------------------------------------------------------------
    def Read(self, argin):
        self.debug_stream( "In " + self.get_name() + "::Read()")
        #    Add your own code here
        try:
            vi = self.__instrument.vi
            vpp43 = self.__instrument._vpp43
            string = vpp43.read(vi, argin)
            #print self.VisaName+": Returning "+cutlongstrings(string, 1000)
            argout = array.array('B', string).tolist()
            return argout
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()
            return ""


#---- Read command State Machine -----------------
    def is_Read_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    ReadLine command:
#
#    Description: Read data until the end
#                
#    argout: DevVarCharArray    Characters readed
#------------------------------------------------------------------
    def ReadLine(self):
        self.debug_stream( "In " + self.get_name() + "::ReadLine()")
        #    Add your own code here
        try:
            string = self.__instrument.read()
            #print self.VisaName+": Returning "+cutlongstrings(string, 1000)
            argout = array.array('B', string).tolist()
            return argout
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()
            return ""


#---- ReadLine command State Machine -----------------
    def is_ReadLine_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    ReadValues command:
#
#    Description: Perform a read command and parses the result finding the different values.
#                It uses the ValuesFormat attribute. If you want to use another format for
#                a specific answer, please, set the ValuesFormat before.
#                Possible formats are: ascii (default), singe, double
#                
#    argout: DevVarFloatArray    List of values read
#------------------------------------------------------------------
    def ReadValues(self):
        self.debug_stream("In " + self.get_name() + "::ReadValues()")
        #    Add your own code here
        try:
            argout = self.__instrument.read_values()
            #self.debug_stream(self.VisaName+": Returning "+cutlongstrings(str(argout), 1000))
            return argout
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- ReadValues command State Machine -----------------
    def is_ReadValues_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Ask command:
#
#    Description: Perform a write command and return the answer from the device.
#                
#    argin:  DevVarCharArray    Command to write
#    argout: DevVarCharArray    Answer from the device
#------------------------------------------------------------------
    def Ask(self, argin):
        self.debug_stream("In " + self.get_name() + "::Ask()")
        #    Add your own code here
        try:
            command = array.array('B', argin).tostring()
            self.debug_stream(self.VisaName+": Asking for "+command)
            string = self.__instrument.ask(command)
            self.debug_stream( self.VisaName+": Returning "+cutlongstrings(string, 1000))
            argout = array.array('B', string).tolist()
            return argout
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()
            return ""


#---- Ask command State Machine -----------------
    def is_Ask_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    AskValues command:
#
#    Description: Perform a write command and return the answer from the device parsed to have
#                a list of values using the attribute ValuesFormat. If you want to use another format for
#                a specific answer, please, set the ValuesFormat before.
#                Possible formats are: ascii (default), singe, double
#                
#    argin:  DevVarCharArray    Command to write
#    argout: DevVarFloatArray    List of values
#------------------------------------------------------------------
    def AskValues(self, argin):
        self.debug_stream("In " + self.get_name() + "::AskValues()")
        #    Add your own code here
        try:
            command = array.array('B', argin).tostring()
            #self.debug_stream( self.VisaName+": Asking for "+command+" values")
            argout = self.__instrument.ask_for_values(command)
            #self.debug_stream( self.VisaName+": Returning "+cutlongstrings(str(argout), 1000))
            return argout
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- AskValues command State Machine -----------------
    def is_AskValues_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Reset command:
#
#    Description: Performs a reset to the device
#                
#------------------------------------------------------------------
    def Reset(self):
        self.debug_stream("In " + self.get_name() + "::Reset()")
        #    Add your own code here
        try:
            self.__instrument.clear()
            self.stopThread()
            self.startThread(1)
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- Reset command State Machine -----------------
    def is_Reset_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#------------------------------------------------------------------
#    Trigger command:
#
#    Description: Send a trigger signal to the device
#                
#------------------------------------------------------------------
    def Trigger(self):
        self.debug_stream("In " + self.get_name() + "::Trigger()")
        #    Add your own code here
        try:
            self.__instrument.clear()
        except Exception as e:
            self.set_state(PyTango.DevState.FAULT)
            self.machineStatus(e)
            self.__connectionEvent.set()


#---- Trigger command State Machine -----------------
    def is_Trigger_allowed(self):
        if self.get_state() in [PyTango.DevState.FAULT,
                                PyTango.DevState.OFF]:
            #    End of Generated Code
            #    Re-Start of Generated Code
            return False
        return True


#==================================================================
#
#    PyVisaClass class definition
#
#==================================================================
class PyVisaClass(PyTango.DeviceClass):

    #    Class Properties
    class_property_list = {
        }


    #    Device Properties
    device_property_list = {
        'VisaName':
            [PyTango.DevString,
            "The name of the device understood by the VISA library",
            [ "SetMePlease" ] ],
        'VisaLibrary':
            [PyTango.DevString,
            "The name of the visa library, default empty string, '@sim' can be used for a simulated device.",
            [ "" ] ],
        }


    #    Command definitions
    cmd_list = {
        'Open':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVoid, ""]],
        'Close':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVoid, ""]],
        'Write':
            [[PyTango.DevVarCharArray, "Command string"],
            [PyTango.DevVoid, ""]],
        'Read':
            [[PyTango.DevUShort, "Characters to read"],
            [PyTango.DevVarCharArray, "Characters readed"]],
        'ReadLine':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVarCharArray, "Characters readed"]],
        'ReadValues':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVarFloatArray, "List of values read"]],
        'Ask':
            [[PyTango.DevVarCharArray, "Command to write"],
            [PyTango.DevVarCharArray, "Answer from the device"]],
        'AskValues':
            [[PyTango.DevVarCharArray, "Command to write"],
            [PyTango.DevVarFloatArray, "List of values"]],
        'Reset':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVoid, ""]],
        'Trigger':
            [[PyTango.DevVoid, ""],
            [PyTango.DevVoid, ""]],
        }


    #    Attribute definitions
    attr_list = {
        'Timeout':
            [[PyTango.DevFloat,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"Timeout",
                'min value':0,
                'description':"Timeout in seconds for all device operations\nDefault value is 5 and you can set it to 0 for\nnon-blocking mode.\nNote that your local VISA library may round up this\nvalue heavily. I experienced this effect with my\nNational Instruments VISA implementation,\nwhich rounds off to 0, 1, 3 and 10 seconds.",
                'Memorized':"true",
            } ],
        'ChunkSize':
            [[PyTango.DevShort,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"ChunkSize",
                'description':"Length of read data chunks in bytes\nDefault value is 20kb",
                'Memorized':"true",
            } ],
        'ValuesFormat':
            [[PyTango.DevString,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"ValuesFormat",
                'description':"Data format for lists of read values\n+) ASCII (the default)\n+) SINGLE\n+) DOUBLE\n+) BIG_ENDIAN\n\nThis attribute is useful with the\nReadValues and AskForValues commands",
                'Memorized':"true",
            } ],
        'TermChars':
            [[PyTango.DevString,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"TermChars",
                'description':"The termination characters for each read and write operation.\nNone (Default)\n\r (CR)\n\ n (LF)\n\nor any combination",
                'Memorized':"true",
            } ],
        'SendEnd':
            [[PyTango.DevBoolean,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"SendEnd",
                'description':"whether to assert END after each write operation\nDefault value is True",
                'Memorized':"true",
            } ],
        'Delay':
            [[PyTango.DevFloat,
            PyTango.SCALAR,
            PyTango.READ_WRITE],
            {
                'label':"Delay",
                'min value':0,
                'description':"Delay time to wait after each write operation\nDefault is 0",
                'Memorized':"true",
            } ],
        }


#------------------------------------------------------------------
#    PyVisaClass Constructor
#------------------------------------------------------------------
    def __init__(self, name):
        PyTango.DeviceClass.__init__(self, name)
        self.set_type(name);
        print("In PyVisaClass  constructor")

#==================================================================
#
#    PyVisa class main method
#
#==================================================================
def main(*args):
    try:
        py = PyTango.Util(*args)
        py.add_TgClass(PyVisaClass,PyVisa,'PyVisa')

        U = PyTango.Util.instance()
        U.server_init()
        U.server_run()

    except PyTango.DevFailed as e:
        print('-------> Received a DevFailed exception:',e)
    except Exception as e:
        pass

if __name__ == "__main__":
	main(sys.argv)