State Notation Language Overview

SNL : State Notation Language
SNC : State Notation Compiler
sequencer : The tool within the IOC that executes the compiled SNL code
Program : A complete SNL application consisting of declarations and one or more state sets
State Set : A set of states that make a complete state machine
State : A particular "mode" of the program in which it remains until a transition statement is evaluated to be TRUE

Basics

The SNL code structure follows a "state transition diagram" format
Once in a given state, "when" conditions are specified under which to leave that state
Action statements are executed during the transition from one state to another
Access to Process Variables via channel access is accomplished by simply "assigning" a PV to a sequence variable

A Complete State Program (with 2 state sets)

-------------------------------------------------------------------------------------------
program level_check        ss volt_check {             ss generate_voltage {                 
                             state light_off {           state init {                        
float  v;                      when (v > 5.0) {         when () {                         
assign  v to "ts1:ai1";          /* turn light on */         vout = 0.0;                     
monitor  v;                      light = TRUE;               pvPut(vout);                    
short  light;                    pvPut(light);               delta = 0.2;                    
assign  light to               ) state light_on;           } state ramp                      

"Indicator_light";          }                           }                                   
                                                                                             
float  vout;                 state light_on {            state ramp {                        
float  delta;                  when (v < 5.0) {         when (delay (0.1)) {              
assign vout to "ts1:ai1";        /* turn light off */        if ((delta > 0.0 &&  
                                 light = FALSE;                vout >= 11.0) ||           
                                 pvPut (light);                (delta < 0.0 &&    
                               } state light_off;              vout <= -11.0))            
                             }                                 /*change direction*/          
                           }                                   delta = -delta;               
                                                             vout += delta;                  
                                                             pvPut(vout);                    
                                                           } state ramp;                     
                                                         }                                   
                                                       }                                     
-------------------------------------------------------------------------------------------

More Basics ...

A state can have multiple "when" statements. The first one to be evaluated to be TRUE will be executed. This allows "conditional branching" within the sequence program.
When entering a state, all "when" statements are evaluated
If no "when" is true, sequence program task "pends" until an event occurs
It is possible to create a "loop" and consume all available CPU

Example of Multiple "whens"

state checks {
  when (interlockChasPwrBi == 0) {
    sprintf(seqMsg1, "Electron Gun Not Ready...");
    pvPut(seqMsg1);
    sprintf(seqMesg2, "Gun Interlock Chassis off");
    pvPut(seqMsg2);
  } state initialChecks
  when (gunLocal) {
    sprintf(seqMsg1, "Electron Gun Not Ready...");
    pvPut(seqMsg1);
    sprintf(seqMesg2, "Egun in local control");
    pvPut(seqMsg2);
  } state initialChecks
  when (gunInterlocksRdyCC == 0) {
    sprintf(seqMsg1, "Electron Gun Not Ready...");
    pvPut(seqMsg1);
    sprintf(seqMesg2, "Interlocks not OK");
    pvPut(seqMsg2);
  } state initialChecks
  when (interlockChasPwrBI && (gunLocal == 0) && gunInterlocksRdyCC) {
    gunAutoStart = 0;
    pvPut(gunAutoStart);
    gunAutoStop = 0;
    pvPut(gunAutoStop);
    sprintf(seqMsg1, "Push Auto-Start to begin autostart...");
    pvPut(seqMsg1);
    sprintf(seqMesg2, "Push Auto-Stop to begin autostop...");
    pvPut(seqMsg2);
%%    taskDelay(60);
  } state waitForRequest
}
state initialChecks {
  when (delay(2.0)) {
    sprintf(seqMsg1, "Initial Checks");
    pvPut(SeqMsg1);
    sprintf(seqMesg2, "");
    pvPut(seqMsg2);
%%    taskDelay(60);
  } state checks
}

Other Features

Assignment of "macros" at program startup (multiple copies of same sequence)
Arrays (each element can be assigned to a PV)
Event Flags (used to sync state sets)
Built-In functions (pg 18 of Manual)

Debugging

seqShow
seqChanShow
printf("Here I am in state xyz \n");
td xxxxxx
ld < my_sequence_program.o
seq &my_sequence_program.o

Examples

Compensate for Attenuator Phase Shift when adjusted
Automatically check timing of BPM's
E-gun startup
Modulator startup
Automatic Test Sequences (240 Inputs to the MPS)
BPM Trajectory Plot

State Notation Language Overview

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