# 3.2.1. Building JULES using FCM¶

FCM is a suite of tools for managing and building source code. In this section, we will be using the build tool - FCM make. FCM make must be given a configuration file that it uses to determine how to build the source code. Extensive documentation on FCM make configuration files is available online.

Help pages for the FCM make command itself (rather than the configuration file) can be accessed using the command:

fcm help make


The FCM configuration file for building JULES is etc/fcm-make/make-local.cfg. This file uses the environment variables below to determine the compiler settings and NetCDF settings to use.

Running FCM make with this configuration file will create 4 new directories in your JULES root directory (i.e. the directory containing docs, src etc.):

.fcm-make
Used by FCM to store information about the build process.
extract
Contains a copy of the code that FCM will build.
preprocess
Contains the code after preprocessing but before compilation.
build
Contains the results of the compilation.

The JULES executable will be produced at build/bin/jules.exe.

## 3.2.1.1. Environment variables used when building JULES using FCM make¶

JULES_CFG_COMP

Used to select compiler specific settings.

Permitted value Purpose
gfortran Default. Use settings for the GNU Fortran compiler.
intel Use settings for the Intel Fortran compiler.
nag Use settings for the NAGWare compiler.
pgf Use settings for the Portland Group compiler.
sun Use settings for the Oracle (previously Sun) Studio compiler series.
JULES_CFG_BLD

Used to select the type of build.

Permitted value Purpose
normal Default. Compile JULES normally.
debug Compile JULES with debug flags.
fast Compile JULES with optimisation flags for faster execution.
JULES_CFG_NCDF

Path to a file defining NetCDF related settings.

Note

Defaults to etc/fcm-make/ncdf/netcdf-dummy.cfg. This will build JULES using a dummy NetCDF library.

If this variable points to any file other than the default, that file must do the following:

• Update $fflags with the flags required to add the NetCDF include path to the compiler’s module search path, e.g.: $fflags = $fflags -I<NetCDF include path>  • Update$ldflags with the flags required to add the NetCDF library path to the compiler’s library search path, and the flags to tell the compiler it needs to link the NetCDF libraries, e.g.:

$ldflags =$ldflags -L<NetCDF library path> -lnetcdf -lnetcdff


The file etc/fcm-make/ncdf/netcdf.cfg is provided as an example of how to set these variables, and should work with most compilers once the correct paths are inserted.

JULES_CFG_ARCH

Path to the file defining compiler related options.

If you use a common compiler, you should never have to set this directly - JULES_CFG_COMP and JULES_CFG_BLD should be used instead.

The default value of this variable is determined by JULES_CFG_COMP and JULES_CFG_BLD. This can be overridden by setting it as an environment variable itself. This way, options for compilers other than those listed above can be specified.

This file must do the following:

• Set build.prop{fc} to the compiler name.
• Update $fflags with the compiler flags to use at compile-time. • Update$ldflags with the compiler flags to use at link-time.

The files in etc/fcm-make/arch can be used as examples of how to do this.

## 3.2.1.2. Example FCM make commands¶

To create a normal JULES executable without NetCDF using the GFortran compiler (taking advantage of the default values for the environment variables):

fcm make -f etc/fcm-make/make-local.cfg


To create a fast JULES executable with NetCDF using the Intel compiler:

export JULES_CFG_COMP=intel
export JULES_CFG_BLD=fast
export JULES_CFG_NCDF=/path/to/ncdf/config.cfg
fcm make -f etc/fcm-make/make-local.cfg


Where /path/to/ncdf/config.cfg looks like:

$fflags =$fflags -I/path/to/netcdf/include
$ldflags =$ldflags -L/path/to/netcdf/lib -lnetcdf -lnetcdff


## 3.2.1.3. Tips for effective use of FCM make (Unix-like systems only)¶

To check the current values of the environment variables JULES will use to build, use the command:

env | grep JULES


If you always use the same compilation options for JULES, consider adding the export lines to the .profile file in your \$HOME directory. Commands in the .profile file are automatically executed in any shell that you open, so defining environment variables there ensures your build environment remains consistent across shells and restarts of your computer. The definitions can still be overridden on the command line if required. For example, to always create a fast JULES executable with NetCDF using the Intel compiler (as above), add the following lines to your .profile:

export JULES_CFG_COMP=intel
export JULES_CFG_BLD=fast
export JULES_CFG_NCDF=/path/to/ncdf/config.cfg


Then to build JULES with those settings, run:

fcm make -f etc/fcm-make/make-local.cfg