01-feb-2007dietrich beck, gsi labview dim-interface motivation event and dim basics idea of lv-dim...

01-Feb-2007 Dietrich Beck, GSI

LabVIEW DIM-InterfaceLabVIEW DIM-Interface

Motivation

Event and DIM Basics

Idea of LV-DIM Interface

Example

Performance


MotivationMotivation

• Large Distributed Systems: One would like to get rid of node names as much as possible.– nodes might change or are replaced– processes might migrate from node to node– where is myResource?

• Need to avoid central bottle-necks.– peer-to-peer connections required– management of many connections can be tedious

• Required– full bandwidth of Ethernet– short latency time

• Can't use protocols or TCP/IP implementation provided by NI


Bad Example: Bad Example: CS CS commands prior to 3.00commands prior to 3.00

LabVIEW message queue or notifier

Caller Callee

node1 node2

Client_node2 Server_node1

LabVIEW TCP/IP

or(!)

callee@node2 callee@node2

DIM TCP/IP


Event basicsEvent basics

• an entity waits for the next event, no polling!

• timeout handling is an important issue

publisher

subscriber subscriber subscriber

client client client

receiver

observer pattern: "one-to-many" command pattern: "many-to-one"

datacommand

example: radio, televisionadded in CS 3.0

example: typical human communicationsole possibility for CS < 3.0


DIMDIM• Distributed Information Management: www.cern.ch/dim

• Maintained at CERN and available via GPL. Thanks to C. Gaspar et al.

• originally developed at DELPHI@LEP/CERN around 1991

• available for a multitude of platforms and languages

• light-weight, aiming at high performance, based on TCP/IP

• today: "backbone" of control systems for LHC experiments

• concept: named services, peer-to-peer connections

DIM server A

DIM server B

DIM client 1

DIM client 2

service "i"

service "ii"

command "iii" DIM name server(negotiates connections)

http://www.cern.ch/dim


Concept of "Named Services"Concept of "Named Services"

• A DIM service is identifier by its name.• A DIM service may exist only once within a DIM domain (If a DIM

server tries to declare a service that already exists, the server is excluded from DIM.).

• Once declared, a service has a fixed type and size (except command services).

• A DIM service can be removed and re-declared.• When subscribing to a service, the DIM client neither needs to know

the name of the DIM server nor the node name.• Once subscribed, DIM automatically (re-)connects the client to the

service or informs the client if the service is not available.• In mixed environments (little/big endian), DIM takes care about byte

and word swapping.


Example for a C/C++ ApplicationExample for a C/C++ Application

DIM dll/so, C. Gaspar, CERN

myApplication

• "serve by routine"– myApplication provides and registers callback functions to DIM

– DIM executes callback functions of myApplication

• "serve by buffer"– myApplication provides memory and registers addresses to DIM

– DIM writes/reads to/from memory of myApplication

uses • write/read memory

• uses callback functions


Using DIM with LabVIEWUsing DIM with LabVIEW

• Difficulties: – LabVIEW does not allow direct execution of code from external

applications (VI Server is not performing enough)– using shared memory would require polling

• Solution: DIMWrapper library written in C– provides callback functions for DIM– callback functions copy data received from DIM to a LabVIEW

message queue or notifier– LabVIEW applications receive data from DIM via message

queue or notifier


New (!) LabVIEW-DIM interfaceNew (!) LabVIEW-DIM interface

DIM dll/so, C. Gaspar, CERN (dedicated patch for LabVIEW)

DIM Wrapper dll/so, GSI LVEvent dll/so, GSI

LabVIEW runtime engine, NI

LabVIEW application

• "serve by routine" only using call back functions with DIM• uses "native" DIM libraries (no re-write)• client and server functionality for commands and services• DIMWrapper (and LVEvent dll) are required to make use of the DIM

callback functionality


Server ExampleServer Example


Client ExampleClient Example


DimWrapper

Example: Change for Example: Change for CS CS commandscommands

LabVIEW message queue or notifier

Caller Callee

node1 node2

Client_node2 Server_node1

LabVIEW TCP/IP

Caller Callee

node1 node2

old:

new:

or(!)

callee@node2 callee@node2

callee DIM TCP/IP


Performance LabVIEW-DIM InterfacePerformance LabVIEW-DIM Interface


ConclusionConclusion

Pros

• LabVIEW-DIM interface provides excellent performance

• no longer care about node names

• based on robust and well established protocol

• using pre-compiled binaries (no re-implementation in LV)

Cons

• no longer pure LabVIEW

• requires experience with message queue or notifiers

• requires use of "typecasts"

Outlook

• DIM-XControls for LabVIEW 8.20 (tomorrow, D. Beck)

• DSC-IO server for LabVIEW 8.20 (tomorrow, H. Brand)

• slight changes of LVEvent library for LabVIEW 8.20 probable

01-feb-2007dietrich beck, gsi labview dim-interface motivation event and dim basics idea of lv-dim...

Documents

dim service

dim domain

dim server b dim client

dim tcpip slide

dim callback functions

peer connections dim

dim basics idea of lv

dietrich beck