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EPICS Sequencer

EPICS Sequencer. Kay Kasemir, SNS/ORNL Many slides from Andrew Johnson, APS/ANL Feb. 2013. IOC. LAN. Channel Access. IOC. Database: Data Flow, mostly periodic processing Sequencer: State machine, mostly on- demand Optional: Sequencer can actually run as standalone CA-Client. Sequencer.

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EPICS Sequencer

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  1. EPICS Sequencer Kay Kasemir, SNS/ORNL Many slides from Andrew Johnson, APS/ANL Feb. 2013

  2. IOC LAN Channel Access IOC • Database:Data Flow,mostly periodicprocessing • Sequencer:State machine,mostlyon-demand Optional: Sequencer can actually run as standalone CA-Client Sequencer Database Device Support I/O Hardware CA Client Sequencer

  3. State Machine 101 .. Is in some State Events trigger transitions Actions are performed on transition State A Event Transition A to B Action State B

  4. Example Start Low vacuum pressure < 5.1 uTorr Open the valve, update pumps, … High vacuum pressure > 4.9 uTorr Close the valve, update pumps, …

  5. Example State Notation Language state start{ when (pressure > .0000051) { RoughPump = 1; pvPut(RoughPump); CryoPump = 0; pvPut(CryoPump); Valve = 0; pvPut(Valve); } state low_vacuum when (pressure <= .0000049) { RoughPump = 0; pvPut(RoughPump); CryoPump = 1; pvPut(CryoPump); Valve = 1; pvPut(Valve); } state high_vacuum } state low_vacuum { …

  6. How it works C Code “SNC” Pre-compiler State Notation Language C Compiler Object code

  7. Advantage • Compiled code. Fast. • Can call any C(++) code • Use #define to create macros, … • Easy connection to Channel Access, Records • Compared to custom CA client, device support, … • Skeleton for event-driven State Machine • Handles threading, event handling, …

  8. When to use the sequencer • For sequencing complex events • E.g. parking and unparking a telescope mirror Photograph courtesy of the Gemini Telescopes project

  9. Disadvantage • Limited runtime debugging • See current state, values of variables. • Can call any C(++) code • and shoot yourself in the foot • Pre-compiler. SNL error • SNC creates nonsense C code • Totally cryptic C compiler messages • Statistically, 95% ofall SNL code • Starts out easy • Evolves • Ends up like this Thom Holwerda,http://www.osnews.com/comics SNL

  10. Should I Use the Sequencer? START CAN I DO THIS IN A DB? Y N CAN I DO THIS IN A DB? Y N USE THE SEQUENCER USE A DATABASE END

  11. If you really want to use SNL • Read the manual http://www-csr.bessy.de/control/SoftDist/sequencer/ • Implement in small steps • Code a little • Compile, test • Code a little more • Compile, test

  12. Walk through the SNL from makeBaseApp –t example

  13. Structure program SomeName /* Variables */ /* State Sets */

  14. Variables double pressure; assign pressure to "Tank1Coupler1PressureRB"; monitor pressure; short RoughPump; assign RoughPump to "Tank1Coupler1RoughPump"; String CurrentState; assign CurrentState to "Tank1Coupler1VacuumState";

  15. State Sets ss coupler_control { state first{ when (pressure > .0000051){ } state low_vacuum when (pressure <= .0000049){ } state high_vacuum } state high_vacuum{ when (pressure > .0000051){ } state low_vacuum } state low_vacuum{ when (pressure <= .0000049){ } state high_vacuum when (delay(600.0)){ } state fault } state fault { } }

  16. Events Variables used in events should be ‘monitor’ed! when (pressure > .0000051) { /* Actions … */ } state low_vacuum when (pressure < 0.000051 && whatever > 7) { } state high_vacuum This is not a wait(10 seconds)! It means: After entering the state, if none of the other when(..) events occur within 10 seconds, do this: when (delay(10.0)) { } state timeout

  17. Actions when (pressure > .0000051){ /* Set variable, then write to associated PV */ RoughPump = 1; pvPut(RoughPump); /* Can call most other C code */ printf("Set pump to %d\n",RoughPump); } state low_vacuum Action statements are almost C code. Above, RoughPump is a state machine variable. The SNL is transformed to printf("Set pump to %d\n", pVar->RoughPump); SNC will add the “pVar->” to all state machine variables that it recognizes. Sometimes it will be necessary to %{ /* Escape C code so that it’s not transformed */ static void some_method_that_I_like_to_define(double x); }%

  18. Sequencer Commands • seq NameOfSequence • Start sequence • seqShow • List all sequences with their ID • seqShow 0x12334 • Detail of seq. • seqChanShow 0x12334 • List variables of seq. • seqChanShow 0x12334, “-” • List variables of seq. • seqStop 0x12334 • Stop a sequence

  19. How to Document SNL • Use /* Comments */ • Manually draw corresponding state diagrams • Maybe try http://ics-web.sns.ornl.gov/kasemir/snl_diags

  20. Summary Sorry, this was more sermon than tutorial • SNL can be useful • Read the SNL manual, be careful

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