12001: Beijing State Notation Language
EPICS
State Notation Language (SNL)
Ned D. ArnoldAPS
(Ron ChestnutSLAC)
22001: Beijing State Notation Language
EPICSState Notation Compiler and Sequencer
Allows programming of sequential state-oriented operations to run in the IOC
The program interacts with the run-time database(s) via channel access
Latest manual : http://mesa53.lanl.gov/lansce8/Epics/sequencer/snl_1.9_man.htmlhttp://mesa53.lanl.gov/lansce8/Epics/sequencer/snl-1.9.ps
32001: Beijing State Notation Language
EPICS
Uses
State machines Startup sequences Enforce prudent operational procedures Watch for likely fault modes that are hard to
detect via alarms Implement complex closed loop control schemes Coordinate control of multiple devices
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EPICS
Advantages
Can implement complicated algorithms Can stop, reload, restart a sequence program
without rebooting (VxWorks property) 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
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EPICSTo be compared with …
CALC records – single equation, interpreted Database programming – complex networks Subroutine Records – arbitrary code
10 input/outputsdbGet….dbNameToAddr
Straight “C” code
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EPICS
Definitions
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 finite state machine
State : A particular mode of the state set in which it remains until one of its transition conditions is evaluated to be TRUE
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EPICS
Basics The SNL code structure follows a state transition diagram format
state light_off { when (v > 5.0){ light = TRUE; pvPut(light); } state light_on }
state light_on { when (v < 5.0){ light = FALSE; pvPut(light); } state light_off }
light_Off state
light_On state
V > 5Turn light on
V < 5Turn light off
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EPICS
Basics (cont …)
Each state has one or more when statements which specify which state to enter next if their condition is met
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
92001: Beijing State Notation Language
EPICSA Complete State Program
(with 2 state sets) program level_check
float v; assign v to "ts1:ai1"; monitor v;
short light; assign light to "ts1:bo1";
float vout; float delta; assign vout to "ts1:ai1";
ss volt_check {
state light_off { when (v > 5.0) { /* turn light on */ light = TRUE; pvPut(light); } state light_on }
state light_on { when (v < 5.0) { /* turn light off */ light = FALSE; pvPut(light); } state light_off }
}
ss generate_voltage {
state init { when ( ) { vout = 0.0; pvPut(vout); delta = 0.2; } state ramp }
state ramp { when (delay(0.1) { if ((delta > 0.0 && vout >= 11.0) || (delta < 0.0 && vout <= -11.0) ) delta = -delta; /* change direction */ vout += delta; } state ramp; }
}
102001: Beijing State Notation Language
EPICSMore 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 conditions are evaluated in the order given in the source code
If no when condition is true, the sequence program task pends until an event occurs, which causes all when conditions to be re-evaluated
It is easy to create a loop and consume all available CPU time When this happens, all CA clients connected to this IOC
will disconnect
112001: Beijing State Notation Language
EPICSExit{} and Entry{}
Extra Clauses which are triggered on ENTRY or EXIT from a state
Default behavior is execution ONLY when making a transition to another state
Default behavior overridden by options (-x and –e)
122001: Beijing State Notation Language
EPICSEntry and Exit example
State ramp_width
option –x;
{
entry{internal_state=RAMP_WIDTH; pvPut(internal_state); ramp_done=0;}
when(ramp_done==1)
{ issue message; } state running
when(delay(.1))
{ do stuff to ramp; check for being done (ramp_done=1) } state ramp_width
exit {publish information on ongoing ramp; taskDelay(1);}
}
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EPICSState Timers (delay())
The delay(seconds) function will test TRUE after seconds delay.
The timer starts each time the state is entered The option –t causes the timer NOT to reset upon
reentry to the same statestate one
option –t;
{
when(delay(10.5)) {timer has expired} state two
when(reset==1) {do something; reset=0; pvPut(reset);} state one
}
state two {}
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EPICSExample of “Multiple whens”
when(interlockChasPwrBI && (gunLocal==0) && gunInterlocksRdyCC) { gunAutoStart = 0; pvPut(gunAutoStart); gunAutoStop = 0; pvPut(gunAutoStop); sprintf(seqMsg1, "Push Auto-Start to begin autostart ..."); pvPut(seqMsg1); sprintf(seqMsg2, "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(seqMsg2, ""); pvPut(seqMsg2);%% taskDelay(60); } state checks }
state checks { when(interlockChasPwrBI==0) { sprintf(seqMsg1, "Electron Gun not ready ..."); pvPut(seqMsg1); sprintf(seqMsg2, "Gun Interlock Chassis off "); pvPut(seqMsg2); } state initialChecks
when(gunLocal) { sprintf(seqMsg1, "Electron Gun not ready ..."); pvPut(seqMsg1); sprintf(seqMsg2,"Egun in local control "); pvPut(seqMsg2); } state initialChecks
when(gunInterlocksRdyCC==0) { sprintf(seqMsg1, "Electron Gun not ready ..."); pvPut(seqMsg1); sprintf(seqMsg2, "Interlocks not OK "); pvPut(seqMsg2); } state initialChecks
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EPICSOther Features
Assignment of macros at program startup for multiple copies of same sequence (must specify +r compiler flag)
program level_check ("unit=ts1")
float v; assign v to "{unit}:ai1";
short light; assign light to "{unit}:bo1";
Arrays (each element can be assigned to a PV) Built-In functions (pg 17 of SNL Manual) Dynamic assignment of PVs to variables Connection Management and status
In startup script …
ld < level_check.o
seq &level_check, "unit=ts1" seq &level_check, "unit=ts2"
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EPICSOther Features
Event Flags (used to sync state sets and monitors) evflag name;
synch PV_name name;monitor PV_name;
efSet(name), efTest(name), efClear(name), efTestAndClear(name)
Escape to C code %% escapes a single line %{ }% escapes a block of code
Log errors to a log file
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EPICSWarnings on Events and Escaped Code
Escaped declarations are file scoped!(even if you use the +r option to create a reentrant program)
If you wish to access variables mapped to PVs in escaped code, you must say pvar->variable_name. Look at the generated “c” code if this is confusing.
Event flags are mapped to #define statementsevflag namex; evflag namey; map to#define namex 1#define namey 2
These events are shared within one task; i.e. one seq & invocation.
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EPICSSome TIME warnings
%% TS_STAMP start_time; TS_STAMP current_time;double elapsed_time;
pvGet(pv_name);current_time = pvTimeStamp(pv_name);TsDiffAsDouble(elapsed_time,¤t_time,
&start_time); Even if the code is reentrant (option +r), start_time and
current_time are file-scoped. seq &prog.o,[one parameter set]
seq &prog.o,[other parameter set]
Will share these variables.
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EPICS
Debugging
seqShow
ioc> seqShowProgram Name Task ID Task Name SS Name
xx_RF_Cond 10854616 xx_RF_Cond l1AutoConditioning
bpmTraject 10838832 bpmTrajectory bpmTrajectorySS
xx_autoPha 10680172 xx_autoPhasing autoPhasing 10573424 xx_autoPha_1 updatePresets
xx_autoRfT 10589876 xx_autoRfTiming autoRfTiming
value = 0 = 0x0
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EPICS
Debugging
seqShow <taskId>ioc> seqShow 10838832State Program: "bpmTraject" initial task id=10838832=0xa56330 task priority=100 number of state sets=1 number of channels=56 number of channels assigned=56 number of channels connected=56 options: async=0, debug=0, newef=0, reent=0, conn=0 log file fd=3 log file name="/tyCo/0"
State Set: "bpmTrajectorySS" task name=bpmTrajectory; task id=10838832=0xa56330 First state = "init" Current state = "waitToPlot" Previous state = "plotWithBeam" Elapsed time since state was entered = 0.4 seconds)
value = 0 = 0x0
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EPICS
Debugging
seqChanShow <taskId>,[“PV_name” or “-”] ioc> seqChanShow 10838832State Program: "bpmTraject"Number of channels=56
#1 of 56:Channel name: "L1:PG1:PM1:BPM.XPOS" Unexpanded (assigned) name: "L1:PG1:PM1:BPM.XPOS" Variable name: "L1PG1PM1_X" address = 11931404 = 0xb60f0c type = float count = 1 Value = 0 Monitor flag=1 Monitored Assigned Connected Get not completed or no get issued Status=11 Severity=2 Time stamp = 05/21/99 16:43:35.085407596Next? (+/- skip count)
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EPICS
Debugging
printf("Here I am in state xyz \n"); string seqMsg1;
assign seqMsg1 to “[PV_name]”;sprintf(seqMsg1, "Here I am in state xyz");
pvPut(seqMsg1); Reload and restart
seqShow td xxxxxx ld < my_sequence_program.o seq &my_sequence_program.o,[parameters]
232001: Beijing State Notation Language
EPICSSequencer programs run also on Hosts
(Re)implemented by APS Main program generated by +m option Option –s on startup creates iocsh, which allows
seqShow, etc. ExampleApp supplied with 3.14 release describes
some details
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EPICS
Examples
Control filling of PEP-II ring Provide handshake between accelerator and
experiment Manage controlled ramping of RF processing Manage shift summaries 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