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State Notation Language (SNL) and Sequencer

State Notation Language (SNL) and Sequencer. April 23, 2012 Kukhee Kim ICD Software SLAC National Accelerator Laboratory. Contents. State Notation Language / Sequencer Definition of Terms State Transition Diagram Example 1: Simple Switch ON/OFF SNL General Syntax & Structures

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State Notation Language (SNL) and Sequencer

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  1. State Notation Language (SNL) and Sequencer April 23, 2012 Kukhee Kim ICD Software SLAC National Accelerator Laboratory

  2. Contents • State Notation Language / Sequencer • Definition of Terms • State Transition Diagram • Example 1: Simple Switch ON/OFF • SNL General Syntax & Structures • Declaration for Variable, Assigment, and Event Flags • Event • Action • Example 2: Life Game • SNL Variables and its Lifetime and Scopes • Dynamic PV assignment • Building SNL code • Runtime Sequencer • Executing SNL Program • Debugging • Additional Features • Advantage of SNL Program

  3. SNL and Sequencer • SNL is “C” like language for programming sequential operations • The sequencer runs program which written in the SNL • Fast execution using compiled code • Common uses • automated start-up and sequencing • fault recovery or transition to safe state • automatic calibration

  4. Sequencer in an IOC LAN Channel Access IOC Sequencer Database Device Support I/O Hardware

  5. Sequencer at CA Client side Tools MEDM Client Client Client MEDM Sequencer LAN Server IOC IOC IOC Meter Power Supply Camera

  6. Definitions • SNL: State Notation Language • SNC: State Notation Compiler • Sequencer: The tool that executes the compiled SNL code • Program: A complete SNL application, consisting declarations and one or more state sets • State Set: A set of states that make a complete finite state machine • State: A particular mode of the state set in which it remains until one of its transition conditions evaluates to TRUE

  7. State Transition Diagram SNL- A tool to implement State Transition Diagram State A Event Transition A to B Action State B

  8. Example 1 – On/Off switch State transition to ON signal Initialize No transition Thresholdto ON State transition to OFF State ON Thresholdto OFF Event: time Action: turn off the light on on off off off State OFF Event: Action: turn on the light

  9. Example 1 – Sneak Look Initialize State ON Event: Action: turn off the light State OFF Event: Action: turn on the light

  10. Example 1 – Sneak Look

  11. SNL: General Structure & Syntax programprogram_name declarations ssstate_set_name { statestate_name { entry { entry action statements } when (event) { action statements } statenext_state_name when (event) { ... } statenext_state_name exit{ exit action statements } } statestate_name{ ... } }

  12. SNL: General Structure & Syntax programname A program may contain multiple state sets. The program name is used as a handle to the sequencer manager for state programs. ssname { Each state set becomes a separate task or thread. statename { A state is somewhere the task waits for events. When an event occurs it checks to see which action it should execute. The first state defined in a state set is the initial state. optionflag; A state-specific option. when (event) { Define events for which this state waits. } statenext Specifies the state to go to when these actions are complete. entry {actions} Actions to do on entering this state. With option -e; it will do these actions even if it enters from the same state. exit {actions} Actions to do on exiting this state. With option -x; it will do these actions even if it exits to the same state.

  13. Declaration: Variables • Appear before a state set and have a scope of the entire program. • Scalar variables intvar_name; shortvar_name; longvar_name; charvar_name; floatvar_name; doublevar_name; stringvar_name; /* 40 characters */ • Array variables: 1 or 2 dimensions, no strings intvar_name[num_elements]; shortvar_name[num_elements]; longvar_name[num_elements]; charvar_name[num_elements]; floatvar_name[num_elements]; doublevar_name[num_elements];

  14. Declaration: Assignments • Assignment connects a variable to a channel access PV name float pressure; assign pressure to "CouplerPressureRB1"; double pressures[3]; assign pressures to {"CouplerPressureRB1", "CouplerPressureRB2", " CouplerPressureRB3"}; • To use these channels in when clauses, they must be monitored monitor pressure; monitor pressures; • Use preprocessor macros to aid readability: #define varMon(t,n,c) t n; assign n to c; monitor n; varMon(float, pressure, "PressureRB1")

  15. Declaration: Event Flags • Event flags are used to communicate events between state sets, or to receive explicit event notifications from Channel Access • Declare them like this: evflagevent_flag_name; • An event flag can be synchronized with a monitored variable syncvar_nameevent_flag_name; • The flag will then be set when a monitor notification arrives, e.g. evflagpressure_event; Sync pressure pressure_event;

  16. Event Event: A specific condition on which associated actions are run and a state transition is made. Possible events: • Change in value of a variable that is being monitored: when (achan < 10.0) • A timer event (this is not a task delay!): when (delay(1.5)) • The delay time is in seconds and is a double; literal constant arguments to the delay function must contain a decimal point. • The timer starts when the state containing it was entered. • Use the state specific option -t; to stop it from being reset when transitioning to the same state.

  17. Event (continued) • The state of an event flag: when (efTestAndClear(myflag)) when (efTest(myflag)) • efTest() does not clear the flag. efClear()must be called sometime later to avoid an infinite loop. • If the flag is synced to a monitored variable, it will be set when the channel sends a value update • The event flag can also be set by any state set in the program using efSet(event_flag_name) • Any change in the channel access connection status: when (pvConnectCount() < pvChannelCount()) when (pvConnected(mychan)) • Any combination of the above event types

  18. Action • Built-in action function, e.g. : • pvPut(var_name); • pvGet(var_name); • efSet(event_flag_name); • efClear(event_flag_name); • Almost any valid C statement • switch() is not implemented and code using it must be escaped. %% escapes one line of C code %{ escape any number of lines of C code }%

  19. Example 2: Life Game

  20. Example 2: Life Game • Basic Rule of Life Game • Rule 1: Any live cell with fewer than two live neighbors died, • as caused by under population. • Rule 2: Any live cell with two or three live neighbors lives • on to the next generation. • Rule 3: Any live cell with more than three live neighbors died, • as if the overcrowding. • Rule 4: Any dead cell with exactly three live neighbors become • a live cell, as if production

  21. Example 2 - Continued • Requirements • 20x20 Bo records to represents cells • Adjustable Initial population density (Ao record, operation range [0. to 1.] • If the initial population density is changed, then starts new game • Initialize cells with random number generator + constraint for the initial population density • Evolution to next generation few times in a second • Provides basic statistics: number of live cells and number of dead cells • Additional Requirement • Monitor the live cell counter in the statistics • If the system reaches to thermal equilibrium (the counter values is not changed during 5 seconds) then, start new game. • To start new game, apply a slight change on the initial population density (use, random walk, init_pop += small random number();)

  22. Example 2 – State Diagram Init Entry: dynamic assignment for 20x20 PVs Event: if the initial population has been changed Entry: Initialize work space with random + initial population density InitArray Exit: Copy work space to the PV assigned variables Make statistics for the current generation Update PVs for display Event: if the initial population has been changed Event: always Run Entry: evolutes cells for next generation Exit: Copy work space to the PV assigned variables Update PV for display Event: if timer has been expired

  23. Example 2: C escapes

  24. Example 2: C escapes

  25. Example 2: Declarations

  26. Example 2: Init State

  27. Example 2: initArray State

  28. Example 2: run State

  29. Example 2: Additional State Set State Set: main_loop State Set: new_game INIT loop Event: expired timer Action: random walk on the initial population Event: changed live cell counter Action: update previous live cell counter to current Live cell counter PV Initial Population

  30. Example 2: Additional State Set

  31. SNL Variable and Scope • Global Variables • lifetime/scope: entire program • Memory allocation by sequencerwith option +r; • Static variable in C with option –r; • Local Variables • State Set • Memory allocation by Sequencer • State • Memory allocation by Sequencer • Entry/Exit/Action function • Stack variable program mySNL option +r; double a; assign a to pvA; monitor a; ssmy_state_set { double b; state low { inti=0; when(a>0.5) { int j ; b = a; i++; for(j=-0;j<MAX;j++) {

  32. SNL Variable’s Scope and Lifetime with Reentrance

  33. SNL Variable’s Scope and Lifetime with Non-Reentrance

  34. Dynamic PV assignments • To allow PV assignment/re-assignment at runtime • Requires an initial assigment (or NULL assignment) in the Declaration Section • for single variables • for array variables double myVar; assign myVar to “”; . . . . . . pvAssign(myVar, “PV_MYVAR”); double myVar[MAX]; assign myVar to { “” }; . . . . . . for(i=0;i<MAX;i++) pvAssign(myVar[i], str_pvName[i]);

  35. Building an SNL Program • Use editor to build the source file. File name must end with“.st” or “.stt”, e.g. “example.st” • “make” automates these steps: • Runs the C preprocessor on “.st” files, but not on “.stt” files. • Compiles the state program with SNC to produce C code: • snc example.st -> example.c • Compiles the resulting C code with the C compiler: • cc example.c -> example.o • The object file example.o becomes part of the application library, ready to be linked into an IOC binary. • The executable file “example” can be created instead.

  36. .st vs. .stt .stt .stt Define Macro in C escape program ex1 Option –r; %{ #define MAX 20 --- nip --- for(i=0;i<MAX;++) { --- }% double myArray[MAX]; ssmyStateSet { state myState { when(index>= MAX) { program ex1 option –r; #define MAX 20 double myArray[MAX]; ssmyStateSet { state myState { when(index>= MAX) { Syntax errorin SNL Illegal to usethe macro in the declaration OK! to usemacro in the C escapeand the SNL code both

  37. .st vs. .stt - continued .st program ex1 option –r; #define MAX 20 %{ --- nip --- for(i=0;i<MAX;++) { --- }% double myArray[MAX]; double my2DArray[MAX*MAX] ssmyStateSet { state myState { when(index>= MAX) { double a[MAX*MAX]; C preprocessing program ex1 option –r; /* #define MAX 20 */ %{ --- nip --- for(i=0;i<20;++) { --- }% double myArray[20]; double my2DArray[20*20] ssmyStateSet { state myState { when(index>= 20) { double a[20*20]; Illegal, becausethe SNC doesn’t have compile time arithmetic OK to use in the local variable inaction/entry/exit function. C compiler does the compile time arithmetic

  38. Runtime Sequencer • The sequencer executes the state program • It is implemented as an event-driven application; no polling is needed • Each state set becomes an operating system thread • The sequencer manages connections to database channels through Channel Access • It provides support for channel access get, put, and monitor operations • It supports asynchronous execution of delays, event flag, pv put and pv get functions • Only one copy of the sequencer code is required to run multiple programs • Commands are provided to display information about the state programs currently executing

  39. Executing SNL Program From an IOC console • On vxWorks: seq &vacuum_control • On RTEMS • seq(&vacuum_control) • On other operating systems: seqvacuum_control • To stop the program • seqStop "vacuum_control"

  40. Debugging • Use the sequencer's query commands: seqShow displays information on all running state programs seqShow vacuum_control displays detailed information on program seqChanShow vacuum_control displays information on all channels seqChanShow vacuum_control,"-" displays information on all disconnected channels seqcar displays information on all channel access channels

  41. Additional Features • Connection management: when (pvConnectCount() != pvChannelCount()) when (pvConnected(Vin)) • Macros: assignVoutto "{unit}:OutputV"; • must use the +r compiler options for this if more than one copy of the sequence is running on the same ioc seq &example, "unit=HV01" • Some common SNC program options: • +r make program reentrant (default is -r) • -c don't wait for all channel connections (default is +c) • +a asynchronous pvGet() (default is -a) • -w don't print compiler warnings (default is +w)

  42. Additional Features – Cont’d • Access to channel alarm status and severity: pvStatus(var_name) pvSeverity(var_name) • Queued monitors save CA monitor events in a queue in the order they come in, rather than discarding older values when the program is busy syncQvar_nametoevent_flag_name [queue_length] pvGetQ(var_name) • removes oldest value from variable's monitor queue. Remains true until queue is empty. pvFreeQ(var_name)

  43. Advantage of SNL Program • Can implement complicated algorithms • Can stop, reload, restart a sequence program without rebooting • Interact with the operator through string records and mbbo records • C code can be embedded as part of the sequence • All Channel Access details are taken care of for you • File access can be implemented as part of the sequence

  44. Acknowledgements • Andrew Johnson, AES basic EPICS Training – January 2011 • Benjamin Franksen, new Seq modules

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