1. pvData,pvAccess,pvIOC,pvService Overview and Status EPICS Meeting
October 2011
PSI Villigen Switzerland Marty Kraimer, Matej Sekoranja and Guobao Shen

2. 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
PSI, Villigen Switzerland Oct 2011
pvData,pvAccess,javaIOC,pvService

3. Accessing Source Code At this time no official releases
Must access via sourceforge project epics-pvdata
Mercurial is code management system
Documentation available at:
PSI, Villigen Switzerland Oct 2011
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4. pvData, pvAccess, pvIOC, pvService
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
PSI, Villigen Switzerland Oct 2011
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5. 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
PSI, Villigen Switzerland Oct 2011
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6. 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
PSI, Villigen Switzerland Oct 2011
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7. 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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8. 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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9. Introspection Example
structure // simple structure
double value
structure timeStamp
long secsPastEpoch
int nanoSeconds
structure // example of array
double[] value
// ...
structure point
structure location
double x
double y
structure // example of structure array
structure[] fieldName
structure point //point is the introspection interface for each element of fieldName
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10. Data Example
structure // simple structure; like introspection but now also values
double value 2.0
structure timeStamp
long secsPastEpoch 0
int nanoSeconds 0
structure // 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
double value .002
double x 1.0
PSI, Villigen Switzerland Oct 2011
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11. Actual Introspection Interfaces
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.
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12. Actual Data Interfaces
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
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13. 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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14. 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
PSI, Villigen Switzerland Oct 2011
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15. 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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16. Channel Get Language Specific
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.
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17. 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
PSI, Villigen Switzerland Oct 2011
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18. 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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19. Status of pvData and pvAccess
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
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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20. 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
PSI, Villigen Switzerland Oct 2011
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21. 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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22. 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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23. 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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24. 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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25. 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!!!!!
PSI, Villigen Switzerland Oct 2011
pvData,pvAccess,javaIOC,pvService

26. 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
If time will demonstrate
A field in a V4 PVRecord accessing V3 or V4 data
channelArray
PSI, Villigen Switzerland Oct 2011
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27. Demo Rest of talk is demo of CAV3<=>pvAccess interoperability
PSI, Villigen Switzerland Oct 2011
pvData,pvAccess,javaIOC,pvService