Difference between revisions of "Future Development Ideas"

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These are my notes for what I think we can/should add to V3 through an evolutionary process.  The ordering is probably vaguely right, but not necessarily that accurate.
These are projects that can/should be added to EPICS V3 using an evolutionary process.  The ordering is not necessarily accurate.




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== Tasks which could be done now ==
== Tasks for the 2014 Codeathon ==


These items can be worked on immediately as they do not depend on any other work to have been completed, and could even be included in the next 3.14 release if appropriate.
These items are of particular interest to have completed before the 3.15.0.2 release in September 2014.


<blockquote>
<blockquote>


=== Documentation (3.14/3.15) ===
=== Bug Triage and Fixing ===


Lots we can do here:
See the [https://bugs.launchpad.net/epics-base Launchpad bug tracker]. Bug
triage involves understanding and replicating the bug and ensuring that it still exists in the latest release. Bugs tagged 'codeathon' are especially appropriate for fixing as Codeathon projects.


* Write a "Building EPICS" guide (chapter in AppDevGuide?)
=== Review Merge Proposals ===
* Restructure the AppDevGuide to make it more accessible
* Convert AppDevGuide into an OpenDocument Text file (keeping index markers)
* Update the Record Reference Manual to 3.14 and beyond (generate tables automatically from DBD files?)
* Look at all the documentation we have and see what's missing
* Data Access, other new CA-related documentation...


The [https://code.launchpad.net/epics-base/+activereviews Launchpad active review] page lists branches which have been proposed for merging.


=== PV Aliases (3.14/3.15) ===
=== Record Reference Manual ===


The ability to add aliases to existing records has already been demonstrated [http://www.aps.anl.gov/epics/tech-talk/2003/msg00707.php by Larry Hoff] and is a desirable feature, although the implementation that goes into Base might be somewhat different.
Work has started on embedding the RRM text inside the record type DBD files, but most record types have still to be documented this way. See ANJ's [https://code.launchpad.net/~anj/epics-base/dbd2html DBD To HTML branch] which contains the work done so far.


* Do we need the ability to add aliases after iocInit()?  There are circumstances where it would be useful, but it might not be thread-safe to allow it.  Need to review database locking to answer this.
=== Dynamic Array Support ===
* Review any Access Security issues.
* Decide how to specify the aliases to the IOC.  I would prefer to extend the DB file syntax rather than use something like Larry's addPvAlias(name, alias) command, but adding alias support to dbLoadRecords() might preclude runtime aliasing.


=== Longer strings using char arrays (3.14/3.15) ===
Neither the CAS nor the PV Gateway support the dynamic array size protocol changes that were added in 3.14.12, and it's starting to show.


Allow an array of DBF_CHAR (or DBF_STRINGs) to be combined in order to put a long string value into a single field that holds more than 40 characters.  Reading a long string back should also be possible somehow.  Support in the IOC is needed, and will also require changes in all CA clients to be able to use this.
=== More test programs ===


There are test programs in libCom/test which cover quite a lot of the libCom functionality, but they are by far from complete.  Writing test code is a very good way to learn the capabilities of the code being tested, and is not usually hard to to, so this would be a good "getting started" project. Specific tests include:


=== Named Soft Events (3.14/3.15) ===
* Tests for each of the Base record types and device support. This should be based on ANJ's [https://code.launchpad.net/~epics-core/epics-base/ioc-test-module/ IOC Test Module] branch so the tests can be written in Perl.
* Any parts of libCom which don't currently have tests in libCom/test (C code)
* Rewrite the tests from the epics-soft-test suite (C or Perl).


Add the ability to use an event name instead of a number in the EVNT field.  EVNT is currently a short, but we only allow soft event numbers to be 8 bits, so this allows us space to add a new set of event numbers for named events.  The event names should not have to be declared in advance, although that does leave the possibility of typos so maybe the IOC should be told first.
=== Convert makeBpt into Perl ===


The makeBpt tool in src/bpt generates non-linear break-point tables from data files.  A fair bit of the C code is concerned with parsing the input file.  There is no particular need for this code to be written in C, speed is not an issue, and eventually I hope to convert all programs needed for building EPICS into Perl code.  Maybe start this project by writing a program to test the output, then convert the C code into Perl.


=== Reload subroutines at runtime (3.14/3.15) ===
=== Support for 64-bit integer fields ===


The genSub can already do this: Allow the subroutine record subroutine name to be looked up after initialization, thus permitting subroutines to be reloaded (on vxWorks anyway).
ANJ has started adding support for DBF_INT64 and DBF_UINT64 types to the database, but the result has not been heavily tested and may not work on all target architectures (in particular VxWorks). See ANJ to work on this.


</blockquote>


=== Timestamp on Value Change (3.14/3.15) ===
== Other Tasks which could be done now ==


Be able to select whether a record's timestamp should indicate when a record last processed (current behavior), or when its value last changed.  Since the timestamp gets set by the record's process() routine, this is best done by adding a menu field to each record type, making the recGblGetTimeStamp() call conditional on that field and add another call to it inside the monitor() routine.
These items can be worked on immediately as they do not depend on any other work to have been completed.


<blockquote>


=== Automated Testing (3.14/3.15) ===
=== Bug Triage and Fixing ===


Convert mrkSoftTest so tests run automatically. If it's easy to run tests they will be run more often...
See the [https://bugs.launchpad.net/epics-base Launchpad bug tracker]. Bug
triage involves understanding and replicating the bug and ensuring that it still exists in the latest release. Bugs tagged 'codeathon' are especially appropriate for fixing as Codeathon projects.


=== Review Merge Proposals ===


=== Extended Device Support ===
The [https://code.launchpad.net/epics-base/+activereviews Launchpad active review] page lists branches which have been proposed for merging.


Asyn's device support layers needs to be converted to Extended support, so their hardware addresses can be changed at runtime.  The same applies to many other device support, but Asyn is probably the largest low-hanging fruit here.
=== Documentation ===


Lots we can do here:


=== EPICS IOC IDE ===
<blockquote>


Starting from Ken Evans' Eclipse IDE for EPICS, make it easy to add new record types and/or device support to an IOC from externally built support modules.  This will probably require adding an XML file to all support modules that describes what they provide and how to integrate them into the IOC application.  This is an Eclipse/GUI programming task and should not require C coding or making any changes to Base.
==== Application Developers Guide ====


* Write a "Building and Porting EPICS" chapter
* Restructure the AppDevGuide to make it more accessible
** Combine the libCom and libCom/osi chapters
** Maybe have a separate section for all callable APIs
** Consider moving API documentation into the appropriate source files and using Doxygen or perldoc to extract it.


=== Rework the devLib Interface ===
==== Other Documents ====


The devLib API is not very well implemented: Some calls are redirected through a function table while others are not; the RTEMS and vxWorks implementations assume that a VMEbus is always available; PCI and its relatives are not handled at all.
* Look at all the documentation we have and see what's missing


There is an out-of-tree implementation of the devLibOSD.c file that the CLS and Australian Synchrotron use on Linux; any replacement must be able to support a plug-in library in a similar manner.
=== VxWorks SMP Support ===


Recent versions of vxWorks (6.8+) support SMP but present a slightly different API that removes intLock() and taskLock(), and replaces taskVar with __thread variables.  The current OSD routines for vxWorks will need significant modification to work with the new APIs.  This will probably require creating a new OS-Class.


</blockquote>
Can obviously only be done by someone with access to vxWorks 6.8 or later.


== Tasks which are already under way ==
=== Extended Device Support ===
 
These tasks are already being worked on but may have stalled.  They might be hard for someone else to take over at this stage.
 
<blockquote>
 
=== Windows Extensions ===
 
Janet Anderson has been working on a R3.14.9 Windows Extensions installer; it might already be out by now.
 
 
=== Time Infrastructure Upgrade (3.14/3.15) ===
 
Babak Kalantari (PSI) is merging the SNS General Time with the Event System code.  If/when finished the result needs to be reviewed and accepted, and the appropriate parts merged into Base.
 
 
=== 3.15 Cleanup ===


3.15 already includes the Up change to the build system; the ramifications of this change have not been followed up completely though:
Experience converting device support layers to Extended support exposed the need to clean up the extended interface, i.e. reduce the code duplication which is currently required since the record knows nothing about the device change.


* Provide a perl script for converting 3.14 apps to 3.15
Libs affected: db, rec.
* Bring over latest templates from 3.14
* Implications for building extensions not worked out
* makeBaseExt.pl is probably no longer needed
* Install local RULES_BUILD files into a top level directory
** Use this dir instead of the configure/O.arch directories so that a <tt>make clean</tt> doesn't remove them...
* Change script installation rules (see ctlsys)


=== More flexible Access Security ===


=== Compiling DBD Files (3.15) ===
The AS design defines each field's security level in the record description, and limits us to only levels 0 and 1.  Some sites may want finer control over accesses: being able to put individual fields of a specific record into a different level, and having additional static levels (use a bitmask?) would help in a number of situations. It is not clear how much work this would entail though.


A Perl implementation of the DBD file parser exists but is incomplete, and I'm hoping to revive this development effort to convert all DBD file information into C tables that get compiled into the IOC executable.
Priority: Low<br>
Libs affected: dbStatic, db, as, ...


With this parser being written in Perl, it will become easier to extend the new facilities that we implement, such as adding new field types (see Variable Length Strings below).
=== Authentication ===


From Ralph: Two or three institutes need a way to password-protect access to certain databases. The usual encryption libraries are freely available, but I guess this issue needs a lot more thinking. Granularity: by record, by connection = IOC, or centralised? Should the authentication last for the client's lifetime or should a short form (some security token or key) be sent with every CA data package?


=== CA Event Filtering (3.15++) ===
=== Secure CA ===


LANSCE's Time and Flavored Data requirements.  It might be wise to do the Unbundling task before merging these changes.
Secure channel access protocol - add SSL wrappers around CA's TCP connections to make them secure.


Jeff's plan is to be able to attach an expression to a channel subscription, which is evaluated by the client's server thread to check each monitor event to determine whether to send it to this client or not.  This could use an enhanced CALC expression parser and evaluation routine to do the expression, we just need a better parser since the expression might include record names.  Discussion about how the values for the expression get saved such that they have the value at the time the data was pushed into the event queue; they might have changed since them.  Jeff's fixed size event that contains those expression value resolves that issue, but it is very restrictive in terms of flexibility.
Libs affected: ca, cas, rsrv


</blockquote>
</blockquote>


== Things which can't be done yet ==
== Things which can't be completed yet ==


These are tasks are waiting for other tasks to be completed before they can be worked on.
These are tasks are waiting on other people or for other tasks to be completed before they can be finished, although there may be infrastructure to support them that can be worked on in parallel.


<blockquote>
<blockquote>


=== Merge Redundancy hooks (?) ===
=== IOCSH Command Registration ===
 
Insert the hooks that DESY needs for redundant control of remote I/O, allowing hot-spare backup IOCs.  I currently have no idea where these hooks are or whether there will be any objections to them.
 
 
=== IOCSH Command Registration (3.15) ===


Add DBD file syntax to convert DBD file information into a C header file which declares the command functions (similar to how we do record types in the current code-base).  This header would then be included by the C file that defines those functions, thus the C compiler would do the work of ensuring that the routine implemented actually matches the command that will call it.
Add DBD file syntax to convert DBD file information into a C header file which declares the command functions (similar to how we do record types in the current code-base).  This header would then be included by the C file that defines those functions, thus the C compiler would do the work of ensuring that the routine implemented actually matches the command that will call it.
Line 136: Line 122:
The command information in the DBD file will also be useful for future versions of the IRMIS parser for st.cmd scripts, where we need to be able to tie the device support configuration commands into IRMIS' need to map hardware devices to record addresses.
The command information in the DBD file will also be useful for future versions of the IRMIS parser for st.cmd scripts, where we need to be able to tie the device support configuration commands into IRMIS' need to map hardware devices to record addresses.


Libs affected: dbHost, all libs Registrar code.


=== Array Field Support (3.15++) ===
=== Link Support ===


Make it much easier to add array fields to record types without having to do as much coding in the record support. See [http://www.aps.anl.gov/epics/core-talk/2007/msg00078.php Ben Franksen email]
See original proposal by ANJ, which needs to be modified to add notify interfaces. This work is already under way, talk to ANJ.


Part of this development (June 2016) includes [[JSON Field Values]].


=== Unbundling (3.15++) ===
=== Array Field Support ===


Split Base into three or more independent modules.  Each module would have its own version number, and the modules can therefore each have an independent existance, although there would obviously be specific dependencies associated with particular versions.
Make it easier to add array fields to record types without having to do as much coding in the record support.  See [http://www.aps.anl.gov/epics/core-talk/2007/msg00078.php Ben Franksen email] and the work done by Nick Rees at the 2009 Codeathon.


If we adopt this, we should bundle working subsets of modules together and release the complete bundle as a tarfile.
Libs affected: dbHost, dbStatic, db, rec.


I see the unbundled modules as follows:
=== Variable Length Strings ===


<blockquote>
The BaseString C++ APIs and classes were developed on the cvs-trunk branch and are being used by Jeff Hill in his replacement IOC server. This interface can form the basis of a new variable length string type for use in the database in addition to DBF_STRING.


==== Core ====
Libs affected: dbHost, dbStatic, db, ...


Depends on: Nothing
=== Alternate DB File Formats ===


These are the common parts used by everything:
There have been calls to be able to replace the existing DB file format with an XML-based format. Currently the DB file parser is too highly integrated into the process of record creation to easily add a second format, but it would be feasible to separate these two and hence allow an expat-based or similar parser to be written. This would probably require a close analysis and upgrade to the locking arrangements of the database. Alternative to XML would be JSON, for which a parser is already being included in the jsonfm branch.
 
* Build system
* libCom & OSI layer
** Basic registry routines
** IOC shell
* Antelope
* Flex
* makeApp tool
 
 
==== Channel Access Client ====
 
Depends on: Core
 
Jeff Hill's responsibility.
 
* CA-specific build rules (probably none)
* CA client library
* CA Tools
* CA application makeApp templates
 
 
==== Channel Access Server ====
 
Depends on: Core, IOC
 
Jeff Hill's responsibility.
 
* CAS-specific build rules (probably none)
* GDD
* The CAS server tool
* RSRV (the old CA server code)
* CAS application makeApp templates
 
 
==== IOC ====
 
Depends on: Core, CAC, CAS
 
The rest is code that runs on the IOC.
 
* IOC-specific build rules
* Static and runtime database access
* Runtime database
* Standard record types
* Soft device support
* The registry (device, driver, record, function)
* IOC application makeApp templates
 
</blockquote>
 
=== Variable Length Strings (3.15++) ===
 
3.15 already includes the BaseString C++ classes in libCom, and I intend to create a set of C wrapper routines for the base class operations (started, currently incomplete).  This can form the basis of a new variable length string type for use in the database in addition to DBF_STRING.
 
 
=== Alternate DB File Formats (3.15++) ===
 
There are calls to replace the existing DB file format with an XML-based format. Currently the DB file parser is too highly integrated into the process of record creation to be able to add a second format, but it would be feasible to separate these two and hence allow an expat-based or similar parser to be written. This would probably require a close analysis and upgrade to the locking arrangements of the database.
 
Need to coordinate with VDCT folks, etc.


Libs affected: dbHost?, dbStatic.


=== New Record API ===
=== New Record API ===
Line 233: Line 161:
From Ben Franksen: Implemented an asyncronous dbGetLinkCallback() routine.  To do this properly though needs an upgrade to the record support API, but maybe could be shoe-horned into the the existing API by adding a dbGetLinkCallback() with a private callback pointer, and we'd require new record types to use this.  What does this do to the device support interface though?  Implications need study.
From Ben Franksen: Implemented an asyncronous dbGetLinkCallback() routine.  To do this properly though needs an upgrade to the record support API, but maybe could be shoe-horned into the the existing API by adding a dbGetLinkCallback() with a private callback pointer, and we'd require new record types to use this.  What does this do to the device support interface though?  Implications need study.


Andrew's Comment: This should be part of the implementation of linkSupport which I proposed in detail many years ago.  The purpose of the "Compiling DBD Files" item above is to make extending the DBD file syntax easier to do in the future, which is a necessary part of that development.


==== Blocking Puts (3.16++) ====
==== Blocking Puts (3.16++) ====
Line 239: Line 168:


The idea is for a version of the SEQ record where rather than a fixed delay, the second link would wait for the completion callback from the first link.  This should be possible today with a special record type, but Tim suggests it should be possible with any link field of any record type.
The idea is for a version of the SEQ record where rather than a fixed delay, the second link would wait for the completion callback from the first link.  This should be possible today with a special record type, but Tim suggests it should be possible with any link field of any record type.
Andrew's Comment: This should be part of the implementation of linkSupport which I proposed in detail many years ago.  The purpose of the "Compiling DBD Files" item above is to make extending the DBD file syntax easier to do in the future, which is a necessary part of that development.




Line 260: Line 191:
if the user has requested something that requires this.  I guess this means the record should include author-defined event types in the wait mask, and special() should be able to generate author-defined events.
if the user has requested something that requires this.  I guess this means the record should include author-defined event types in the wait mask, and special() should be able to generate author-defined events.


==== Online Record Creation (3.16++) ====
With good database locking, it might be feasible to look at the ability to add new record instances at runtime, and maybe delete as well.  This would probably need a change to the record interface to initialize the new instances.


</blockquote>
</blockquote>
Line 270: Line 197:


After converting the DBD load process into table registration, it should become easier to allow support modules (containing record types, device support and other drivers) to be discovered and loaded dynamically.  Unloading is a very different matter though, we don't have the shutdown facilities to allow that.
After converting the DBD load process into table registration, it should become easier to allow support modules (containing record types, device support and other drivers) to be discovered and loaded dynamically.  Unloading is a very different matter though, we don't have the shutdown facilities to allow that.
=== Atomic Operations through CA (3.16++) ===
This is related to the Asynch Gets issue above; implement Read-Write (Swap, permits semaphores), Process-Read and Write-Process-Read (Command/Response) as atomic operations available through Channel Access.


</blockquote>
</blockquote>

Latest revision as of 19:51, 1 June 2016

These are projects that can/should be added to EPICS V3 using an evolutionary process. The ordering is not necessarily accurate.



Tasks for the 2014 Codeathon

These items are of particular interest to have completed before the 3.15.0.2 release in September 2014.

Bug Triage and Fixing

See the Launchpad bug tracker. Bug triage involves understanding and replicating the bug and ensuring that it still exists in the latest release. Bugs tagged 'codeathon' are especially appropriate for fixing as Codeathon projects.

Review Merge Proposals

The Launchpad active review page lists branches which have been proposed for merging.

Record Reference Manual

Work has started on embedding the RRM text inside the record type DBD files, but most record types have still to be documented this way. See ANJ's DBD To HTML branch which contains the work done so far.

Dynamic Array Support

Neither the CAS nor the PV Gateway support the dynamic array size protocol changes that were added in 3.14.12, and it's starting to show.

More test programs

There are test programs in libCom/test which cover quite a lot of the libCom functionality, but they are by far from complete. Writing test code is a very good way to learn the capabilities of the code being tested, and is not usually hard to to, so this would be a good "getting started" project. Specific tests include:

  • Tests for each of the Base record types and device support. This should be based on ANJ's IOC Test Module branch so the tests can be written in Perl.
  • Any parts of libCom which don't currently have tests in libCom/test (C code)
  • Rewrite the tests from the epics-soft-test suite (C or Perl).

Convert makeBpt into Perl

The makeBpt tool in src/bpt generates non-linear break-point tables from data files. A fair bit of the C code is concerned with parsing the input file. There is no particular need for this code to be written in C, speed is not an issue, and eventually I hope to convert all programs needed for building EPICS into Perl code. Maybe start this project by writing a program to test the output, then convert the C code into Perl.

Support for 64-bit integer fields

ANJ has started adding support for DBF_INT64 and DBF_UINT64 types to the database, but the result has not been heavily tested and may not work on all target architectures (in particular VxWorks). See ANJ to work on this.

Other Tasks which could be done now

These items can be worked on immediately as they do not depend on any other work to have been completed.

Bug Triage and Fixing

See the Launchpad bug tracker. Bug triage involves understanding and replicating the bug and ensuring that it still exists in the latest release. Bugs tagged 'codeathon' are especially appropriate for fixing as Codeathon projects.

Review Merge Proposals

The Launchpad active review page lists branches which have been proposed for merging.

Documentation

Lots we can do here:

Application Developers Guide

  • Write a "Building and Porting EPICS" chapter
  • Restructure the AppDevGuide to make it more accessible
    • Combine the libCom and libCom/osi chapters
    • Maybe have a separate section for all callable APIs
    • Consider moving API documentation into the appropriate source files and using Doxygen or perldoc to extract it.

Other Documents

  • Look at all the documentation we have and see what's missing

VxWorks SMP Support

Recent versions of vxWorks (6.8+) support SMP but present a slightly different API that removes intLock() and taskLock(), and replaces taskVar with __thread variables. The current OSD routines for vxWorks will need significant modification to work with the new APIs. This will probably require creating a new OS-Class.

Can obviously only be done by someone with access to vxWorks 6.8 or later.

Extended Device Support

Experience converting device support layers to Extended support exposed the need to clean up the extended interface, i.e. reduce the code duplication which is currently required since the record knows nothing about the device change.

Libs affected: db, rec.

More flexible Access Security

The AS design defines each field's security level in the record description, and limits us to only levels 0 and 1. Some sites may want finer control over accesses: being able to put individual fields of a specific record into a different level, and having additional static levels (use a bitmask?) would help in a number of situations. It is not clear how much work this would entail though.

Priority: Low
Libs affected: dbStatic, db, as, ...

Authentication

From Ralph: Two or three institutes need a way to password-protect access to certain databases. The usual encryption libraries are freely available, but I guess this issue needs a lot more thinking. Granularity: by record, by connection = IOC, or centralised? Should the authentication last for the client's lifetime or should a short form (some security token or key) be sent with every CA data package?

Secure CA

Secure channel access protocol - add SSL wrappers around CA's TCP connections to make them secure.

Libs affected: ca, cas, rsrv

Things which can't be completed yet

These are tasks are waiting on other people or for other tasks to be completed before they can be finished, although there may be infrastructure to support them that can be worked on in parallel.

IOCSH Command Registration

Add DBD file syntax to convert DBD file information into a C header file which declares the command functions (similar to how we do record types in the current code-base). This header would then be included by the C file that defines those functions, thus the C compiler would do the work of ensuring that the routine implemented actually matches the command that will call it.

The command information in the DBD file will also be useful for future versions of the IRMIS parser for st.cmd scripts, where we need to be able to tie the device support configuration commands into IRMIS' need to map hardware devices to record addresses.

Libs affected: dbHost, all libs Registrar code.

Link Support

See original proposal by ANJ, which needs to be modified to add notify interfaces. This work is already under way, talk to ANJ.

Part of this development (June 2016) includes JSON Field Values.

Array Field Support

Make it easier to add array fields to record types without having to do as much coding in the record support. See Ben Franksen email and the work done by Nick Rees at the 2009 Codeathon.

Libs affected: dbHost, dbStatic, db, rec.

Variable Length Strings

The BaseString C++ APIs and classes were developed on the cvs-trunk branch and are being used by Jeff Hill in his replacement IOC server. This interface can form the basis of a new variable length string type for use in the database in addition to DBF_STRING.

Libs affected: dbHost, dbStatic, db, ...

Alternate DB File Formats

There have been calls to be able to replace the existing DB file format with an XML-based format. Currently the DB file parser is too highly integrated into the process of record creation to easily add a second format, but it would be feasible to separate these two and hence allow an expat-based or similar parser to be written. This would probably require a close analysis and upgrade to the locking arrangements of the database. Alternative to XML would be JSON, for which a parser is already being included in the jsonfm branch.

Libs affected: dbHost?, dbStatic.

New Record API

These requests all need a significant change to the record support API. They are also fairly closely related, so should be used as input into any new API that gets devised.

Asynchronous Gets (3.16++)

From Tim Mooney: It would be great if an input link could initiate processing, and get a value that is known to be the result of that processing, even if records to be processed are asynchronous. Currently, a record that needs completion-qualified data must know how to trigger the processing that generates that data.

From Ben Franksen: Implemented an asyncronous dbGetLinkCallback() routine. To do this properly though needs an upgrade to the record support API, but maybe could be shoe-horned into the the existing API by adding a dbGetLinkCallback() with a private callback pointer, and we'd require new record types to use this. What does this do to the device support interface though? Implications need study.

Andrew's Comment: This should be part of the implementation of linkSupport which I proposed in detail many years ago. The purpose of the "Compiling DBD Files" item above is to make extending the DBD file syntax easier to do in the future, which is a necessary part of that development.

Blocking Puts (3.16++)

From Tim Mooney: It would be nice to have a link attribute that could put, request processing, and wait for completion. We have this capability now, in dbCaPutCallback(), but it's selectable only at DCT time.

The idea is for a version of the SEQ record where rather than a fixed delay, the second link would wait for the completion callback from the first link. This should be possible today with a special record type, but Tim suggests it should be possible with any link field of any record type.

Andrew's Comment: This should be part of the implementation of linkSupport which I proposed in detail many years ago. The purpose of the "Compiling DBD Files" item above is to make extending the DBD file syntax easier to do in the future, which is a necessary part of that development.


Multiple Master problem (3.16++)

From Jeff: Changes to output values in a PLC or similar device initiated outside of the output record. This could be resolved adding a new routine to the RSET that the device support calls back when it has a new raw ouptut value to back-propagate to the VAL field. Currently done by some devices that set PACT and call the record's process() routine to use its second-half processing only.


Records Can't Block (3.16++)

From Tim Mooney: I think almost half the code in the sscan record is devoted to bookmarking. In the middle of some algorithm, the record needs to wait for external events; the only way back in is process(), and so the record has to have a complicated arrangement of switches that get it back into the algorithm it was executing, with enough state information to decide what to do next. At the same time, the record must check to see if it's now processing because of some out-of-band request from the user. Normal and exceptional processing must, therefore, be mixed together in the switch arrangement, and adding new behaviors to the record becomes a very hairy undertaking.

But what the record would really like to do is just wait with its context intact for events, and allow special() to release it from the wait if the user has requested something that requires this. I guess this means the record should include author-defined event types in the wait mask, and special() should be able to generate author-defined events.


Dynamically Loaded Modules (3.16++)

After converting the DBD load process into table registration, it should become easier to allow support modules (containing record types, device support and other drivers) to be discovered and loaded dynamically. Unloading is a very different matter though, we don't have the shutdown facilities to allow that.

Atomic Operations through CA (3.16++)

This is related to the Asynch Gets issue above; implement Read-Write (Swap, permits semaphores), Process-Read and Write-Process-Read (Command/Response) as atomic operations available through Channel Access.

Retrieved from "https://wiki-ext.aps.anl.gov/epics/index.php?title=Future_Development_Ideas&oldid=3813"