Creating a State Machine (Sequencer)

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Contents

• Introduction
• Create State File
  • Call State file from IOC
• Start any sequence programs
  • Notes
• Passing macros into the sequencer

Introduction

Does your IOC require definitive states? If the logic of your IOC will go beyond calc fields, you may wish to implement a Finite State Machine.

EPICS supports State Machine creation with a set of Sequencer tools. The state file, which controls the states the system can be in and the transitions between them, is written in C-based State Notation Language. This is a how-to guide to create and implement a state machine into your IOC.

Create State File

Enter the support directory of your IOC, e.g.:

C:\Instrument\Apps\EPICS\support\HFMAGPSU\master\HFMAGPSUSup

Create a state file in this directory (e.g. fsm.st). The EPICS manual for SNL files can be found here.

If you are reading or changing PV values, the following must be included in your fsm.st file

#include "seqPVmacros.h"

A copy of seqPVmacros.h can be found here and should be in the folder alongside the fsm.st file.

Create a fsm.dbd file, which contains the following:

registrar(fsmRegistrar)

Make sure that your .dbd file has a different name to the IOC .dbd file. Otherwise, your IOC .dbd file will be overwritten.

Edit the Makefile in this folder, to reference your new .dbd and .st files and add the libraries needed for them.

TOP=..
include $(TOP)/configure/CONFIG
#=======================================

# Install .dbd and .db files
DATA += devHFMAGPSU.proto
DBD += fsm.dbd

# Sequence file
SRCS += fsm.st
LIBRARY_IOC = HFMAGPSU
HFMAGPSU_LIBS += seqDev seq pv
HFMAGPSU_LIBS += $(EPICS_BASE_IOC_LIBS)

#=======================================
include $(TOP)/configure/RULES

Call State file from IOC

Enter IOC folder, e.g.

(cd …EPICS\ioc\master\HFMAGPSU\iocBoot\iocHFMAGPSU-IOC-01)

Add the following to the end of the st-common.cmd file:

< $(IOCSTARTUP)/postiocinit.cmd
epicsEnvSet(P,$(MYPVPREFIX)$(IOCNAME))

## Start any sequence programs
seq fsm, "P=$(P)"

In the above example, we are passing the name of the IOC through to the fsm.st file so we can reference PVs in it with {P}:.

Enter the IOC source folder (e.g. HFMAGPSU-IOC-01App\src)

Edit build.mak to ensure the needed libraries are included:

# Add all the support libraries needed by this IOC
## ISIS standard libraries ##

$(APPNAME)_LIBS += seqDev seq pv

Notes

Whenever you make an edit to the fsm.st file, rebuild the support module:

cd …EPICS\support\HFMAGPSU\master
make

Passing macros into the sequencer

You can pass macros into your sequencer by including them in brackets after you define the program. E.g.

program keithley_2001 ("P, channels")

Here P and channels are passed as macros to the state machine. You pass these to the state machine in the st.cmd file when calling the state machine. E.g.

seq keithley_2001, "P=$(MYPVPREFIX)$(IOCNAME):, channels=10"

To access these macros in your state machine, create a variable to hold your macro, e.g. char *P for the macro P, and call macValueGet on your macro, e.g. P = macValueGet("P"), within your state machine to allow you to use the macro "P" within your code as the variable "P".

Note that the macros you pass into the state machine must match up with those in your .db files. Otherwise your state machine will not be able to assign variables to PVs and the state machine won't run.