Release Notes for Version 2.2

Release 2.2.9

  • install build rules in the modern way (if available)

    This allows installation into the same directory as EPICS base and other modules, e.g. when packaging for Debian.

    The configure/RULES_BUILD is replaced with configure/RULES_SNCSEQ and gets installed via CFG. For compatibility with base-3.14, configure/RULES_BUILD now includes the configure/RULES_SNCSEQ. The rules are protected against multiple inclusion with a variable definition (like with C headers).

    Thanks to Michael Davidsaver <> for the patch (slightly modified).

  • snc: better error messages when file operations fail

    Instead of calling perror, we now use strerror and our internal ‘report’ function to conveniently compose a more detailed error message.

  • snc, build rules: improve behavior when compilation fails

    This changes snc so that it either doesn’t touch the output file at all or else removes it if there was an error. In addition, the build rules are changed so that output files are removed before trying to create them.

    Thanks to Johnson, Andrew N. <> for analysis and patch (slightly modified, all errors are mine).

  • tests: add test for (non-)existence of output file

  • docs: fix code examples in tutorial

    Thanks to for the reporting these.

Release 2.2.8

This relase only fixes a build problem on MacOS.

Release 2.2.7

Bug fixes:

  • fix: pvGet should not request more elements than the channel has

    Otherwise the CA call will fail and we get no data at all.

    Thanks to Dejan Kocjan <> for finding the cause of this problem and proposing the fix.

  • tests: extend array test with pvPut and pvGet

    This tests that both work as expected even if the declared array size is shorter or longer than the native array size of the PV.

  • fix a bug in seqMacParse

    When the value of a parameter is the unquoted empty string as in “var=”, this would not be recognized and the default value was used instead. Just a stupid unnecessary explicit test I had to remove. Thanks to Hovanes Egiyan for reporting this problem.

  • Fix build problems in examples/ on Windows

    The script generates code that on Windows requires symbols named in the DBD file to be linked from an DLL, not from a directly-linked source file. When main() is directly linked with an object file containing a registrar entry, we can call that registrar code directly from main() as done here instead of using the generated code.

    These build errors may only appear when using a MinGW compiler, either native or as a cross-build running on another OS.

  • fix PROD_LIBS definition in test/unit/Makefile

    Thanks to Michael Davidsaver <> for spotting this.

  • fix: add missing braces around if body in seqShowAll

  • fix #if expression to determine whether base < 3.14.10

Various minor improvements:

  • build: add standard includes to configure/{RELEASE,CONFIG_SITE}
  • examples/demo: use $EPICS_HOST_ARCH in
  • add a small example to test program parameters
  • docs: adapt how to invoke the demo program
  • docs: made blockdiags a bit more readable

Release 2.2.6

Building against EPICS base 7.x:

  • locally define USE_TYPED_RSET to avoid deprecation warnings
  • fix definition of EPICS_HAS_UNIT_TEST for base versions > 3

Also made a few minor changes to the documentation.

Release 2.2.5

  • docs: use RMDIR instead of rm -rf for clean target in the Makefile

    This fixes (harmless but annoying) error messages on Windows.

  • snc: use to generate the dependencies

    This fixes error messages and sometimes also build failures during parallel builds on Linux machines iwth many cores. These are caused by EPICS build rules not passing -MD to gcc when generating dependencies for C source files.

  • snc: fixed C90 incompatibility in the parser template, see Known Problems in Release 2.2.4.

Release 2.2.4


  • seq: fixed a possible race condition with pvAssign

    The problem concerns access to the dbch member of CHAN: the runtime pvAssign may free this pointer (and also sets it to NULL); on the other hand, the CA callbacks need to access it, or else must return immediately. There was a test that checks if dbch is NULL but it was not locked against concurrent access from pvAssign, which could lead to an assertion failure or worse to invalid memory accesses.

  • seq: in pvFlushQ test that queue and associated event flag of the channel actually exist before accessing them.

    This fixes possible crashes when using this function with non-queued or queued but non-synced channels.

  • pv: fix test for result of epicsTimeGetCurrent

    This change fixes a problem with EPICS base-3.16, which adds more error codes to epicsTime.

  • lemon: updated lemon.c and the parser template from upstream

    This was done to avoid 64 bit problems that the native Windows compiler warned about, since such problems are usually handled quite efficiently by the sqlite maintainers. Unfortunately the latest version of the parser template had a serious bug that could result in compiler crashes. This bug has been fixed in the sequencer (and reported, but not yet fixed, in the upstream version). This in turn uncovered a weakness in the compiler tests, see below.


  • fixed errors in section “Asynchronous Use of pvPut” of tutorial

    Thanks to Christian Pulvermacher <> for spotting this.

build system:

  • snc: turn LEMON into an absolute path with base 3.15

    This fixes a build problem on some Windows versions which don’t like relative path names for commands when the output is redirected to a file.

  • snc: extra dependency avoids (harmless) errors when generating .d files

  • snc: simplify the multi-target lemon rule

    Instead of generating an intermediate file (“parser_created”) we now use a pattern rule. This is the more reliable (and recommended) way to make rules with multiple targets work as expected.

  • test only for BASE_3_14==YES

    Testing for 3.15 doesn’t make sense (yet), as the majority of changes will be needed for 3.16 and later versions, too. Testing BASE_3_15==YES will be reserved for incompatibilities between 3.15 and 3.16 etc.

  • avoid deprecation warnings for use of PATH_FILTER with base 3.15

  • snc: make recipe for snl.bnf atomic


  • moved test for invalid state change statement to compiler tests

  • moved demo programs from test/validate to examples/small

    The programs are only compiled as TESTPROD_HOST to avoid cluttering the install directories any further; db files can be served using the standard softIoc binary from base.

  • added to examples

  • refactor killing background IOCs

  • test that snc terminates normally on all input programs

    Previously, in case snc crashes on some input file, it was possible that this was not detected by the tests.

Release 2.2.3

Thanks to the new co-maintainer Freddie Akeroyd <> this release fixes building and running the tests for Windows7 in 32 and 64 bit, both with cygwin and native compiler. Please note that parallel building may not work on Windows yet.

A few bugs have been fixed and some minor improvements made here or there, for details see the list below.


  • cast 0 to Node* in varargs call to node constructor
  • added a missing include to types.h
  • explain apparently missing var init in a comment
  • fix warnings and error when DEBUG is defined


  • Initialise timeNow

    Required for running tests with windows debug build

  • fix default put during a pending async put

    Attempting to issue a DEFAULT pvPut even when an ASYNC put is already pending on the same variable led to an assertion failure. This is now fixed.


  • cleaned up the prim_types mess, snc no longer depends on seq library

    Making the compiler depend on the seq library was a bad idea, since the names of the primitive types were the only thing that snc needed from seq.

    Instead I added a new src/common subdir that installs (and for seq_release.h generates) the header files that are shared between the compiler and the runtime. The epicsShare stuff has been removed from seq_prim_types.h. A new preprocessor symbol (declare_prim_type_names) makes sure that the prim_type_name and prim_type_tag_name variables are visible only inside the runtime library and the compiler and not in generated sequencer programs.


  • Set PATH for running tests in shared build

    The path to seq.dll needs to be set in cygwin and Windows for running tests when built with SHARED_LIBRARIES=YES

  • Fix running tests on Windows

    The *Ioc.t tests were hanging on windows when run from Make - they worked when ran individually from the command line, but were not then killing the background IOC process on test completion. Using the Win32::Process package rather than fork() to create subprocesses fixes both issues

  • set environment variables in a more portable way

  • silence warnings about different TOP dirs

  • ensure that tests cover seq exit phase

  • Reorder test linking for cygwin

    Move subThreadSleep.c to separate library to enable correct import/export declarations for linking on cygwin

  • enable pvSync with or without db

  • set HARNESS_ACTIVE env var in queueTest.plt

  • use a per host “unique” CA server port

    The idea here is to isolate concurrent test runs on the same machine against each other. The port is set to 10000 + pid % 30000, which is not unique in a strict sense, but the probability of a collision is quite small and the solution is non-intrusive and very simple to implement.


  • link specific code into a library instead of main

    This fixes problems for cygwin-x86 arch.

build system:

  • added include of meta build configuration to configure/RELEASE
  • removed configure/RELEASE.win32-x86

Release 2.2.2

The bugs listed in Known Problems in Release 2.2.1 have been fixed.

In addition, some of the tests and parts of the test infrastructure have been changed so as to produce clean TAP files (this is currently only supported by base-3.15 with ‘make tapfiles’). For the same reason, the usual messages when a program starts are no longer issued with printf, but rather with errlogSevPrintf(errlogInfo,…).

Some improvements to the web pages have been made: the version the pages refer to is more prominently visible, some shortcuts have been renamed, and side-bar shortcuts to all other (maintained) versions were added.

I added git mirrors of the darcs repos, the URLs are:

Release 2.2.1

This is the first release of version 2.2 of the sequencer. The following describes what has changed relative to version 2.1.

Supported EPICS Base Versions

This version drops support for base versions older than, all others should work fine.

If you manage to compile the sequencer with earlier base versions, well, good for you. It’ll probably work, too. I will also accept patches that restore lost compatibility with older base versions, provided they achieve this without unduly complicating the code base or build system.

New Language Features

Foreign Types

It is now possible to use foreign types (i.e. types declared in C code, such as structs, enums, unions, and typedefs) in variable declarations, type casts, and the special “sizeof” built-in operator. Previously existing restrictions as to which type expressions are allowed have been lifted, so that (almost) everything you can say in C is now supported in SNL, too. Particularly, function types are now supported in declarations and type expressions, as well as indirect calls in expressions.

There are two notable limitations:

  • Using C type aliases (defined in C with typedef) is allowed, but you must prefix the type name with the new keyword typename (which I borrowed from C++). Supporting foreign typedefs without any extra markup as in C would require lots of extra effort which IMO is not justified.
  • There is only limited support for defining your own types (see Type Definitions below) and you cannot mix type definition with type usage (for instance in a variable declaration) as in C.

The words enum, struct, typename, union, and void are reserved words now and can no longer be used as identifiers.

Other Foreign Entities

A side effect of allowing indirect calls is that there is no longer any syntactic distinction between using functions and using variables. This means that issuing warnings just for the use of undeclared foreign variables is no longer possible. If they are still undeclared in the generated C code, the C compiler will warn you anyway. You can enable extra warnings (+W, see New Option for Extra Warnings below) to get these warnings, but that will report foreign functions, too.

A related change is that struct or union members are no longer identified with variables in the SNL syntax; members are no longer considered to be foreign entities (but for compatibility you can still list them in a foreign declaration).

Function Definitions

You can now define functions in SNL. The syntax is like in C and you can call the built-in PV functions inside them. This is made possible by passing the execution context (the state set identifier and the variable block pointer) as hidden parameters.

You may pass all kinds of variables to such a function, but for channel (“assigned”) variables their special “assigned” status gets lost when passing them, similar as when passing them to a C function. This means you can call e.g. pvGet(x) in the body of an SNL function, but only if x is a global variable.

My various attempts to lift this limitation were the main reason it took me so much longer than I had expected to make this release. In order not to hold up the release of version 2.2 any longer, I decided to postpone this feature to a future release.

Type Definitions

You can now define your own struct types in SNL (other type formers like union and enum are not yet supported). As usual the syntax is a (simplified: no bit fields) variant of the C syntax. This is currently not very useful, since there is no way to “assign” struct members to PVs. Lifting this limitation is closely related to passing channel arguments to functions and therefore postponed, too.

New Option for Extra Warnings

The new option:+W (off by default) enables extra warnings, that you normally don’t want to see. Currently this warns you once for each foreign entity that appears in the program.

Deprecated and Removed Features

Deprecated Foreign Declarations

The so called “foreign entity declarations”, introduced in version 2.1, have become obsolete (see Other Foreign Entities) and are therefore deprecated.

Deprecated State Local assign etc

Using an assign, monitor, sync, or syncq clause inside a state is now deprecated. This was never very useful to begin with, and gets in the way of some future improvements.

Removed Keyword “connect”

This alias for the “assign” keyword, also introduced in version 2.1, is no longer supported. I believe nobody actually uses it, and the next version will introduce a completely new syntax for that feature anyway. I can demote the removal to a deprecation warning if it turns out that this seriously hurts people.

With hindsight, introducing this was a bad idea, as were foreign declarations and state local assign.

Removed PV Library

The PV library has been almost completely eliminated. What remains is a thin layer over CA, implemented in C, and offering only the functionality that is actually needed by the sequencer. The API is similar (but not identical) to the old C API; particularly, all the pvStat, pvSevr, and pvType definitions are as before.

The documentation for the PV layer has been removed, too. The only remaining user relevant part of the interface is contained in pvAlarm.h, see Built-in Constants.

Also removed were the Keck examples and the KTL related stuff in other example directories.

Removed devSequencer

The (broken and ugly) sequencer device support was removed. Consequently, seqFindProgByName was be removed as it is no longer needed.

Built-in Constants

All built-in constants are now known to snc and therefore no longer treated as foreign entities. Particularly, using them no longer gives “undefined variable” warnings, even with extra warnings enabled (+W). They are also documented in the reference.

The snc-generated C code for built-in constants now uses the name of the constant, instead of its value. This makes the code a bit more readable and slightly simplifies code generation.

The variables ssId and pVar are (somewhat irregularly) treated as built-in constants, too. This makes it possible to call C functions that take them as a parameter directly from inside SNL code without having to escape the call. That is, you can now write such calls as

my_c_fun(ssId, pVar, ...);

instead of

%%my_c_fun(ssId, pVar, ...);

Built-in Functions

Reported Severity of Failures

The severity of timeouts and usage errors reported on the console has been demoted from errlogFatal to errlogMajor. Reporting them as fatal has misled users in the past to think that their running program instances have become unstable now, which is definitely not the case for this sort of errors.


The built-in function pvMessage now consistently returns a failure string describing the problem whenever anything with the passed channel variable went wrong. This particularly applies to any failure status returned from the CA layer.

New Delay Implementation

While it was always allowed to use arbitrary SNL expressions for the argument to delay, even expressions that could change their value at any time (e.g. because they contain monitored variables), this did not work as one would expect. In fact, the delay expression would be evaluated just once for all delays appearing in conditions inside a state when the state was entered. Later checks whether the delay has expired used the cached delay value.

In the new (much simpler) implementation, delay expressions are evaluated like all other parts of the state transition condition. Delay IDs no longer exist and the code generator treats calls to delay like any other built-in function. The effect of delaying the state transition is now achieved (completely internal to the implementation of seq_delay) by adjusting the minimum time to wait for events (if the delay has not yet expired). The run-time system no longer stores the delay, but rather the (future) time when the wake-up should happen, leading to more accurate timing of delays.

Since calling delay outside of the condition of a state transition never had any useful effect, it is now disallowed.


The prototype of the underlying C function seq_delay() has changed to support the new implementation. If there is code out there which calls this function from the C side, I’d venture that it is broken anyway and should be fixed.


Unlike the assign clause, the dynamic pvAssign function does not substitute program parameters (previously sometimes referred to as “macros”) in the channel name. There is now a new function pvAssignSubst that behaves exactly like pvAssign except that it substitutes program parameters in the channel name, just like assign does.

PV Functions and Multiply Assigned Arrays

A long time wart of the sequencer, inherited from the 2.0 version, was the behaviour of built-in PV functions when you pass an array in which elements are assigned to separate PVs. In most cases (except one, see below) this behaved as if you had passed in just the first element of the array, which is inconsistent and error-prone.

However, existing programs might (perhaps without the author or maintainer being aware of it) rely on the current behaviour – and silently breaking such programs seems like a bad idea. Instead, this is now a compile time error. The error message contains a hint how the user can fix their program (“perhaps you meant to pass xxx[0]?”) so that it retains its old behaviour.

For some of the PV functions, operating on all contained PVs of a multi-PV array would make sense if one would be willing to overload them. I decided against that and instead provide a number of new functions named “pvArray…”:

I may add pvArrayGet and pvArrayPut in the future. Especially for the SYNC variant, such functions could be implemented (much) more efficiently than the semantically equivalent loop over all elements of the array.


The C side equivalents seq_pvArray… are not (yet) part of the public API. The reason is that in version 2.3 they will get a slightly different type. You can use them in embedded C code but if you do that you should be aware that your program might not work or even build with version 2.3.

Timeout Arguments for pvGet and pvPut

For both pvGet and pvPut there is now the possibility to specify a timeout that differs from the default of 10 seconds. This is done by giving an extra argument after the SYNC keyword, as in:


As before, the default behaviour for pvGet(var) i.e. neither an explicit SYNC nor ASYNC, is synchronous, unless option -a is in effect. In this case, or if SYNC is given with no extra argument, the standard default timeout of 10 seconds is assumed.

In contrast to previous releases of version 2.2, the C equivalents are unchanged with respect to version 2.1. Instead, the compiler generates calls to seq_pvGetTmo or seq_pvPutTmo which have the additional argument.

New Built-in Functions pvGetCancel and pvPutCancel

It is now possible to cancel and asynchronous get or put request by calling pvGetCancel or pvPutCancel, or the channel array variants pvArrayGetCancel or pvArrayPutCancel, respectively.

Generated C Code

Order of Definitions

The first change here is that the generated variable block is now placed after all other top-level definitions that appear in the program before the first state set, in particular before escaped C code. In previous versions, this was the other way around. The second change is that for all other top-level definitions the order is retained exactly as in the SNL source file.

This was done so that foreign type declarations can be used in global (SNL) variable declarations. This concerns types imported via %%#include as well as types defined in escaped C code.

Note that this means that escaped C code that appears before the first state set cannot access global variables declared in SNL, even if the re-entrant option is not in effect. Such C code should now be placed after the last state set.

Anyway, it is my hope that the possibility to write functions directly in SNL will make the escape-to-C route mostly obsolete.

Names of Generated Entities

These now follow a strict naming convention:

Generated names start with seqg_.

In particular, struct UserVar became struct seqg_var, and the implicit parameters ssId and pVar are now named seqg_ss and seqg_var, respectively. Because these three identifiers are often referenced in escaped C code, I have added compatibility aliases for them, so as not to break existing programs. See External API below for details.

In order to prevent name clashes, words starting with seqg_ are no longer valid identifiers in SNL.

I am aware that there may be cases where this change breaks existing programs which heavily rely on escape to C code. If this is the case, please shout! Adding more compatibility aliases can be done any time.

Event Flags

The compiler now generates variables for event flags to make it easier for escaped C code to call event flag functions (seq_ef*).

External API

I finally got around to separating the public API (to be called from e.g. embedded C code) from the internal interface between the compiler generated code and the run-time system. The latter parts have been moved from seqCom.h to the new header file seq_snc.h.

In particular, the following changes have been made:


  • includes of pvAlarm.h and seq_release.h
  • enum compType and its members DEFAULT, ASYNC, SYNC
  • typedefs string, SS_ID, seqBool, seqProgram
  • all functions except seqRegisterSequencerProgram and seqRegisterSequencerCommands but including seq_pvIndex (which is actually a macro)


  • new built-in functions:
    • seq_pvGetCancel
    • seq_pvPutCancel
    • seq_pvAssignSubst
  • the constant DEFAULT_TIMEOUT (see New Delay Implementation)


  • EV_ID -> EF_ID
  • VAR_ID -> CH_ID

Compatibility Aliases

#define ssId                  seqg_ss
#define pVar                  seqg_var
#define USER_VAR              SEQ_VARS
#define UserVar               seqg_vars
#define VAR_ID                CH_ID
#define EV_ID                 EF_ID
#define seq_pvFreeQ           seq_pvFlushQ
#define DEFAULT_QUEUE_SIZE    100

These names should not be used in new code.


  • DELAY_ID (obsolete, see New Delay Implementation)
  • OPT_MAIN (-m is a compile time option)
  • optTest (is now internal to seq library)

Moved to seq_snc.h

  • struct definitions for the static part of the generated program:

    • struct seqChan
    • struct seqState
    • struct seqSS
    • struct seqProgram
    • typedef PROG_ID
  • option constants:

    • OPT_CONN
    • OPT_SAFE

    User code never needs to use these. It can use seq_optGet instead.

  • bitmask operations:

    • NBITS
    • NWORDS
    • bitSet, bitClear, bitTest

    Like option values, these were never meant to be part of a public API.

  • the constants TRUE and FALSE

  • typedefs for generated functions; note that these have been renamed, too

  • the functions seqRegisterSequencerProgram and seqRegisterSequencerCommands

Other Changes

  • epicsShareAPI markers have been removed except for shell commands


My justification for making these potentially breaking changes is that this is how it should have been done from the start. The things I have removed were never meant to be part of a public API. In the unlikely event that there are existing programs with a legitimate need to access these internals, they can always include seq_snc.h.

Build System

Top-level Makefile

The extra rules in the top level Makefile to produce documentation with or without generating a pdf file have been changed: ‘pdf’ and ‘docs’ are no longer make variables. Instead there are a number of new targets you can specify:

  • html: build the docs in html format
  • docs: additionally build the manual in pdf format
  • upload etc: these are for my own benefit only, ignore them

See Building the Manual for details.

Generate st.d Files

The extra build rules for the sequencer have been extended to generate dependencies for .st files, using the tool from base. Note that .st files are passed through the C preprocessor and therefore may include C header files or in fact SNL code from another file.

Bug Fixes

  • Place program lock around wake-up commands in CA callback.

    This prevents a race condition resulting in a crash when the program shuts down and deletes mutexes etc before the callback has issued its final ss_wakeup call.

  • Fixed connect and monitor accounting in seq_disconnect and seq_camonitor.