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Ways to modify OpenIFS

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There are several ways in which code changes to OpenIFS could be managed and these are described in this article.

We do not recommend that the source code in the oifs/src directory is edited directly as this can make it difficult to track changes and update to new versions. We recommend all code changes are maintained outside the main src directory. There are several ways in which code changes to OpenIFS could be managed:

Copy entire source

Copy the entire oifs/src to (for example) oifs/mysrc and work on the copy. The build configuration files can also be copied if required to, say, oifs/mymake. For instance you might make a new version of oifs/make/fcmcfg/oifs.cfg for your own changes.

Multiple copies of the src directory could be used for different experiments.  The use of a version control system is recommended to track changes. The difficulty with this approach is the full source needs to be copied which makes integrating changes different and changed files are hard to see.

Copy only changed/new source

Leave code in oifs/src 'as-is' and place only modified or new code in separate directories but link to pre-compiled code in oifs/make.  This has the advantage that multiple code developments can be maintained in separate directories; code changes are easy to see and integrating new versions of the model source straightforward. A version control system can also be used.

This makes use of a facility provided by the FCM build software called 'inherited builds'. This is explained below in a series of examples.

Inherited builds with FCM

In essence an inherited build is one in which a pre-build (i.e. compilation) of OpenIFS is used or inherited by a new FCM configuration file placed in a separate directory. The new FCM configuration file only needs to specify what's different about the build, either the sources or compilation settings. The rest of the information is obtained by telling FCM to look at the already  compiled OpenIFS. A user may have a number of these separate configuration files each in separate directories for developing or testing independent code changes.


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Warning

The information on this page is correct for OpenIFS version 38r1. For OpenIFS 40r1 please change 'build.prop' to 'oifs.prop'. This page will be updated with new examples.

For assistance either email openifs-support@ecmwf.int or use the OpenIFS User Forums.


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oifs_inherit_examples.tar.gz.

Save the tarfile in your oifs directory, where the main OpenIFS tarfile was unpacked.

This tarfile will create several directories: mymake, mysrc1, mysrc2 and mysrc3.



...

Example1: Modifying compilation options

HowTo customise compiling OpenIFS explains how environment variables and editing the configuration files can alter the compiler settings for OpenIFS. In this simple example, an inherited build is used to achieve the same effect by creating a separate configuration file.

...

As in the main 'make' directory, FCM has created a 'build' subdirectory which in this case only contains the object file of the routine uvclr and a new executable. You now have the original executable in 'oifs/make/build/bin/master.exe' and this modified one for testing/debugging.

To run this new executable as a test, edit the job script in the t21test directory and alter the line: MASTER= to point to the location of the newly built executable.

Info

Experiment with this example by adding additional lines in the

Info

Experiment with this example by adding additional lines in the change-fcflags.cfg file and verify that the 'fcm make' command shows those routines being recompiled.

To verify the new compiler options are being used add the -vv flag to the fcm make command to see all output i.e. fcm make -vv or look in the FCM log file which can be found in the file .fcm-make/log.

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Note that FCM has: seen the new version of cnt0.F90, recompiled it and relinked it to the pre-compiled object code in oifs/make. The new executable can be found in the build/bin sub-directory. As in example 1, to try out this new executable in the t21test directory edit the script and change the line MASTER= to point to the location of this executable.

A more advanced example with modules

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titleFCM output (shortened)
% fcm make -v -f new-src.cfg 
[init] make
[init] make config-parse
[info] config-file=/openifs/inherit_tests/oifs/mymake/new-src.cfg
[done] make dest-init
[init] make build
[info] analyse  0.0 newsrc/newsub.F90
[info] analyse  0.0 ifs/module/yemct0.F90
[info] analyse  0.0 ifs/control/cnt0.F90
[info] sources: total=2193, analysed=3, elapsed-time=0.5s, total-time=0.0s
[info] target-tree-analysis: elapsed-time=13.2s
[info] compile    0.0 M yemct0.o             <- ifs/module/yemct0.F90
[info] compile+   0.0 M yemct0.mod           <- ifs/module/yemct0.F90
[info] ext-iface  0.0 U cnt3.intfb.h         <- ifs/control/cnt3.F90
[info] compile    0.0 U cnt2.o               <- ifs/control/cnt2.F90
[info] ext-iface  0.0 U cnt0.intfb.h         <- ifs/control/cnt0.F90
[info] compile    0.1 U cnt3.o               <- ifs/control/cnt3.F90
[info] compile    0.1 M cnt0.o               <- ifs/control/cnt0.F90
[FAIL] make build          # 25.4s
[FAIL] make                # 25.6s
[FAIL] mpif90 -obin/master.exe /media/hugetmp/Backedup/openifs/inherit_tests/oifs/make/build/o/master.o -L/var/tmp/tmpdir/nagcuser/jtmp.6858/LvpNtq0TxD -lmaster -fopenmp /home/rd/openifs/software/grib_api/1.9.18/grib_api-gcc-4.5.0/lib/libgrib_api_f90.a /home/rd/openifs/software/grib_api/1.9.18/grib_api-gcc-4.5.0/lib/libgrib_api.a -L/usr/local/apps/lapack/3.4.1/LP64 -llapack -lblas -lm # rc=1
[FAIL] /var/tmp/tmpdir/nagcuser/jtmp.6858/LvpNtq0TxD/libmaster.a(cnt0.o): In function `cnt0':
[FAIL] /media/hugetmp/Backedup/openifs/inherit_tests/oifs/mysrc3/ifs/control/cnt0.F90:101: undefined reference to `newsub_'
[FAIL] collect2: ld returned 1 exit status

...

Additional help can be found in the compiling and FCM OpenIFS Frequently Asked Questions page.

The OpenIFS forums can be used to ask questions to the OpenIFS community and support team.

Any questions or problems can also be sent direct to the OpenIFS support team at: openifs-support@ecmwf.int.

 

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