pvData,pvAccess,pvIOC,pvService Overview and Status

EPICS MeetingOctober 2011

PSI Villigen Switzerland

Marty Kraimer, Matej Sekoranja and Guobao Shen

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Outline of Talk

Brief Description of pvData, pvAccess, pvIOC, and pvService

Status of Java, C++, and Python implementations

Communication between channel access V3 and pvAccess

Demo of CAV3 <=> pvAccess communication

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Accessing Source Code• At this time no official releases

– Must access via sourceforge project epics-pvdata• Mercurial is code management system• Documentation available at:

– http://epics-pvdata.sourceforge.net

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pvData, pvAccess, pvIOC, pvService

pvData Memory resident structured data Introspection and data interfaces

pvAccess– Network support for pvData

pvIOC – much like a V3 IOC– Record + database of records

• A record has a top level structure– Record scanning – periodic and event– support – no distinction between record and device support

• any field can optionally have associated support• standard: alarm, timeStamp, scan etc.• extensible – can be used wherever appropriate

pvService– Service layer for High Level Applications– Current emphasis

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Overview of pvData

Memory resident structured data Based on concept of structure of fields Introspection and data

– Client can discover what data looks like without passing data– Once the interface is known a data container can be created

A field has:– A field name– A type

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Field Type

Type is one of– scalar – a scalar has an associated scalar type– array – All elements have the same scalar type– structure – a structure of fields

• Each field has unique name within the structure• Each field has it's own type

– structureArray – an array of structures• All elements have the same introspection interface

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Scalar Type

Scalar Type is one of the following:– boolean - has the value true or false– byte - 8 bit signed integer– short - 16 bit signed integer– int 32 - bit signed integer– long - 64 bit signed integer– float - 32 bit IEEE float– double - 64 bit IEEE float– string - string

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Property Structures

A Property Structure is:– Provides the type of data that V3 provides via the DBR types– A “well known” structure, e. g. of special interest– Has associated “helper” code– Provides data for some of the V4 Standard Data types

The following properties are currently supported– enum– timeStamp– alarm– display– Control

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Introspection Example

structure // simple structure double value structure timeStamp long secsPastEpoch int nanoSecondsstructure // example of array double[] value // ...

structure point double value structure location double x double ystructure // example of structure array structure[] fieldName structure point //point is the introspection interface for each element of fieldName // ...

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Data Example

structure // simple structure; like introspection but now also values double value 2.0 structure timeStamp long secsPastEpoch 0 int nanoSeconds 0structure // example of array double[] value [1.0,2.0,3.0]

structure // example of structure array structure[] fieldName structure point double value .001 structure location double x 0.0 double y 0.0 structure point double value .002 structure location double x 1.0 double y 0.0

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enum Type {scalar,scalarArray,structure,structureArray}interface Field { Type getType(); String getFieldName(); ...}Interface Structure extends Field { Field[] getFields();...}// other definitions

Language Specific enum definitions for Type and ScalarType Interface Definitions: Field, Scalar, ScalarArray, Structure, and StructureArray Factory for creating instances Above provides a flavor of how things are defined.

Actual Introspection Interfaces

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interface PVField { Field getField(); PVStructure getParent(); // other other methods}interface PVDouble extends PVScalar{ double get(); void put(double value);}// many more definitions

Language Specific PVField, PVScalar, PVStructure, PVStructureArray For each scalar type:

– PVBoolean, ... , PVString– PVBooleanArray, ... ,PVStringArray

Many interfaces Factory for creating objects of all supported types Conversion Facility provided Above gives a flavor of how things are defined

Actual Data Interfaces

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Overview of pvAccess

Supports network access to pvData Protocol is language and platform independent Client/server oriented Multiple providers are supported

– Each must make data look like pvData Design emphasis is efficient use of network

– Multiple messages per network packet– Big messages automatically span network packets

Large Array Support:– In addition to array automatically spanning network packets

• Can copy directly from data source to network buffer• Can copy directly from network buffer to data sink• But must override default implementation

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Connect to a Channel

A Channel is a connection from a client to a server To create a channel a client

– Calls channelAccess to get a provider (must give provider name)– Calls the provider to create a channel (must give channel name)

A request to connect to a channel results in:– A UDP broadcast of the channel name– A UDP directed message from server to client– A TCP connection between client and server

In the server a channel is a connection to a top level structure– In a pvIOC the channel is actually a connection to a V4 record– A record holds a top level structure

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Channel Methods

Channel provides the following methods:– getField – get the introspection interface for the channel– createChannelProcess – request processing– createChannelGet – get data from the server– createChannelPut – put data to the server– createChannelPutGet – put and get with single request– createChannelRPC – channel Remote Procedure Call– createChannelArray – put/get sub-array– createMonitor – monitor the data

With the exception of getField– Client and server both create a container to hold the data– A container is a top level PVStructure– Client can request arbitrary set of field in server top level structure

The following slide shows channelGet

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interface Channel extends Requester{ ChannelGet createChannelGet( ChannelGetRequester channelGetRequester, PVStructure pvRequest);}interface ChannelGetRequester extends Requester { void channelGetConnect( Status status,ChannelGet channelGet(PVStructure pvStructure,BitSet bitSet); void getDone(Status status);}interface ChannelGet extends ChannelRequest { void get(boolean lastRequest);}

Language Specific pvRequest specifies what client wants to get.

– Fields desired and other options. See documentation for details. ChannelGetConnect receives

– The client side data container– A bitSet that shows what data has changed since last get

Once created multiple gets can be requested. Only changed data transferred ChannelPut, etc have similar facilities.

Channel Get

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Overview of pvIOC

A pvIOC has the following– A database of PVRecords

• Has a name• has a top level PVStructure

– Record Processing– Support optionally attached to any field of record– Record scanning: passive, periodic, and event– On-line add/delete of records– PortDriver – successor to asyn– Similar to V3 IOC but supports pvData instead of flat records

The record name is the channel name for pvAccess

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Overview of pvService

The service concept is discussed in other talks during this session A pvService is a service where client and server communicate via pvAccess Server side can be implemented via support connected to a PVRecord Remote Procedure Call semantics can be implemented via one of

– channelPutGet or channelRPC• ChannelPutGet returns data via existing PVStructure• channelRPC returns a new PVStructure for each request

Example is gather service– It allows the client to get/put/monitor a set of V3 channels.– Each V3 channel can be either a scalar or an array.

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Status of pvData and pvAccess

PvData– pvDataJava is complete Java implementation– pvDataCPP is a complete C++ implementation– Work is in progress on a Python implementation (Guobao Shen)

PvAccess– PvAccessJava is a complete Java implementation– PvAccessCPP is a complete C++ implementation– Work is in progress on a Python implementation (Guobao Shen)– Communication between Java and C++ works

The C++ implementations use epics base for:– Build system– Uses libCom for Threads, events, etc.

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Status of pvIOC

pvIOCJava has lots of features:– All features mentioned in pvIOC summary– BUT almost no portDriver support for talking to hardware

• Can not take advantage of all the C/C++ asyn support pvIOCCPP has very few features but does have

– Is implemented in a regular V3 IOC.– V3Channel provides access to V3 records via pvAccess– Has base classes that support service development– Lots of work remaining

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Status of pvService

Service layer for High Level Application Client/server model pvData/pvAccess for communication between client and server

The following services have been implemented– itemFinder Service

• Given a search string return a list of channel names and properties

• channelFinder will be used instead of itemFinder– createGather Service

• Given a list of channels create a new gather record– gather Service

• Get/put/monitor a set of channels• Examples:

– BPMs for a bump or golden orbit– Correctors for a bump or golden orbit

– Model server• Interface to model server: Elegant, etc.

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Status of pvService continued

PvServiceJava– Both client and server side of everything shown on previous slide

PvServiceCPP– Client side of createGather and gather

• C++ implementation• Python implementation

– Uses the C++ implemention– Has no knowledge of pvData– Provides array data as numPY arrays

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Current State

PvData and pvAccess (both Java and C++) work PvIOCJava

– Extensive support• Analog I/O, Digital I/O, Successor to calc, etc• There are test databases that demonstrate these and more

– PortDriver• Works but only minimal drivers and no Streams• VXI11 support, i.e. GPIB devices

PvService– Gather ready for use

• Server: Java only• Client: Java, C++, Python

– Prototypes for some others (Java only)

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Priorities

Immediate:– Start generating releases

• Currently no real users• Just Matej, Guobao, and myself• Must be ready for users and additional developers

– Get Java versions working properly• Switching from CVS to mercurial• Make maven the build environment

– Until now just used default eclipse build system Intermediate

– Get end users to use the createGather and gather services– Agree on and implement other services.

Future– Still lots more to do.– Next slide gives one vision

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Vision For Future

Implement all of what is in pvIOCJava in pvIOCCPP pvIOVJava portDriver provides functionality of asynManager but cleaner

– BUT• Almost no portDrivers• No synApps• No area detector• Etc etc• Sigh!!

When portDriver is implemented in pvIOCCP– Can use all existing portDrivers– Can use lots of area detector– Can use lots of synAPPs– Can provide structured data to/from portDriver clients!!!!!

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Interoperability CAV3 <=> pvAccess

Using a pvIOCJAVA access PVRecord data via– V3 caget, caput, camonitor– V4 pvget, pvput– Using the V4 swtshell

Using a pvIOCCPP access V3 records via– V4 pvget, pvput– Using the V4 swtshell

If time will demonstrate– A field in a V4 PVRecord accessing V3 or V4 data– channelArray

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Demo

Rest of talk is demo of CAV3<=>pvAccess interoperability