EPICS Overview

Table of Contents

EPICS System Architecture: Physical
EPICS System Architecture: Logical
Basic Attributes Of Epics
Hardware - Software Platforms (Vendor Supplied)
Basic Control System Components
Channel Access
Database
Record Processing
Database Scanning
IOC Summary
Channel Access Summary
OPI Summary

EPICS System Architecture: Physical

EPICS System Architecture: Logical

Basic Attributes Of Epics

• EPICS IS NOT THE CONTROL SYSTEM!!!
  
  • EPICS is a collection of software tools and other components
    
  • Application Developers use EPICS to create control system
    
• Tool Based
  
  • Minimize Custom Coding
    
  • Uniform Operator Interface
    
• Completely Distributed
  
  • No Single Bottle-Neck
    
  • Scales Nicely
    
  • IOC is autonomous system
    
• Event Driven
  
  • No Polling
    
  • Quick Response
    
• High Performance
  
  • Workstation (Sun4)
    
    • >2000 screen updates per second
      
    • Quick Display Call-up (goal of < 2 seconds)
      
  • IOC (68040)
    
    • Process >5000 records per second.
      

Hardware - Software Platforms (Vendor Supplied)

• OPI
  
  • Hardware
    
    • UNIX based Workstation (currently sun4)
      
  • Software
    
    • UNIX Operating System
      
    • X Windows
      
    • Motif Toolkit
      
• LAN
  
  • Hardware
    
    • Ethernet/FDDI Now
      
    • ATM
      
  • Software
    
    • TCP/IP Protocols via sockets
      
• IOC
  
  • Hardware
    
    • VME bus and crates
      
    • Motorola 68020, 68040, 68060 (Power PC in future)
      
    • Various VME/VXI modules: ADCs, DACs, Binary Input, Binary Output, etc.
      
    • Allen Bradley Scanner (Most Allen Bradley I/O modules)
      
    • GPIB devices
      
    • BitBus devices
      
  • Software (vxWorks)
    
    • Real time kernel
      
    • Extensive "Unix like" libraries
      

Basic Control System Components

• OPI Tools
  
  • Display Editor/Manager - Graphics tool monitor&control displays
    
  • Database Configuration Tool
    
  • State Sequence Compiler
    
  • Alarm Handler
    
  • Archiver
    
  • BURT - Backup/Restore Tool
    
  • Interfaces to Commercial Products (IDL,Wingz, Mathematica, etc)
    
  • Programs, e.g. automatic beam tuning, can be interfaced via Channel Access
    
• LAN
  
  • Channel Access
    
• IOC
  
  • Memory Resident Database
    
  • Database Access
    
  • Database Scanners
    
  • Record Support
    
  • Device Support
    
  • Driver Support
    
  • Sequencer (Finite State Machine)
    
  • Custom Code
    

Channel Access

• Client/Server Model
  
  • Clients
    
    • UNIX, IOC, VMS, Windows NT (Some)
      
    • Future: ?
      
  • Servers
    
    • Today: IOC
      
    • Future: ?
      
• A client can communicate with an arbitrary set of servers
  
• A server accepts connections from an arbitrary set of clients
  
• Supporting a new OS and/or CPU means porting client (relatively easy)
  
• Basic Functions
  
  • Search - Locate process variables, Establish connections
    
  • Get - Get value of process variable + extra info (alarm status, etc.)
    
  • Put - Change value of process variable
    
  • Add Event - Add change of state callback (alarm status, value change)
    

Database

• Memory resident
  
• Records can be added/deleted only via a database configuration tool
  
• Some field values, e.g. links, can be modified only via DCT
  
• Most field values can be changed dynamically
  
• Multiple record types
  
  • AI - Analog Input
    
  • AO - Analog Output
    
  • CALC - Calculation
    . . . (Currently 27 supported record types)
    
  • Each record type has fixed set of fields
    
    • Common to all record types
      
      • NAME - Unique identifier for record
        
      • STAT - Alarm Status
        
      • SEVR - Alarm Severity
        . . .
        
    • Record specific
      
      • I/O values
        
      • Links to other records
        
      • High/Low Operating Ranges
        
      • Alarm Limits (HIHI, HIGH, LOW, LOLO)
        . . .
        

Record Processing

• Some combination of the following
  
  • Read Inputs
    
    • Analog Inputs
      
    • Binary Inputs
      
    • Fields from other database records
      
  • Conversion
    
    • None
      
    • Linear
      
    • Break Point Tables
      
  • Write Outputs
    
    • Analog Outputs
      
    • Binary Outputs
      
    • Fields in other database records
      
  • Check for Alarms
    
  • Trigger Monitors (Channel Access callbacks)
    
  • Trigger processing of linked records
    
• Relatively easy to add new Record types
  
• Device Support (relatively easy to add new devices) hides hardware details
  
  • Several different ADCs supported. All use same record support module
    
  • Same for Analog Outputs, Binary I/O, Timers, etc.
    
• Device Drivers for complicated I/O interfaces
  

Database Scanning

• Determines when a record is processed
  
• Event Scanning - Triggered by sequence program or some other program
  
• Periodic Scanning - Current rates vary from .1 secs to 10 secs
  
• I/O Event Scanning - Triggered by external interrupt, i.e. driver interrupt routine
  
• Passive - Triggered by other records being processed
  

IOC Summary

• Autonomous device to control a subsystem
  
• OPI, via Channel Access, has easy access for control and monitoring
  
• Control algorithms can be implemented via scanning and record links
  
• Sequencer provides a general purpose software tool modeled as a finite state machine
  
• Other special purpose support can be added to an IOC
  
• Relatively easy to add new record and device support
  
• A single 68040 IOC can process >5000 records/sec
  

Channel Access Summary

• Transparent LAN access from client to multiple servers
  

OPI Summary

• Graphics Editor allows relatively easy creation of monitor&control displays
  
• Monitor&control displays can handle >2000 screen updates/sec
  
• Alarm Handler
  
• Archiver
  
• Other Applications can communicate via Channel Access