1. Look at your domain and set l_obc_east=.true. if there is an open boundary at the east of your domain (.false. otherwise). Same remark for the western, northern and southern boundaries.
2. What kind of physics do you want to introduce through the open boundaries ?
2.1.a Do you want to propagate tides (you probably have several ranks in your configurations) ? If so, set l_obc_tide=.true. (.false. otherwise and do not take care of the following variables)
2.1.b If you want to read harmonic components from a file :

• l_tide_harmcompo=.true.,
• specify the path of the file : file_tide_harmcp='/export/home11/mars/DATA/TIDES/FES2004/fes2004_oco1.2.nc'
• (You must have previously compiled your code with -Dkey_tide_fes2004 or another CPP key)
• If the previous rank supplies the barotropic open boundary conditions that are saved in a file of the form obc2d_BISC.rank1_BISC.suffix (l_obc2drank_save=.true. for this previous rank) :

2.1.c l_tide_harmcompo=.false., the executable automatically reads the obc2d_BISC.rank1_BISC.suffix file
2.2.a Do you want to couple your model with another OGCM ? If so, set l_obc_ogcm=.true. (l_obc_ogcm=.false. and do not take care of the following variables)
(use the tool named "extract" to prepare the open boundary fields, i.e. to interpolate the OGCM fileds onto your current grid)
2.2.b for each open boundary, specify the path of the file containing the OBC fields : file_obc_ogcm_n='/export/home11/mars/CONFIG/BISC/DATA/BISC_obc_north_2000_2004.nc' for the northern boundary for instance
2.2.c specify which field you want to read (whatever the location of the open boundary) : Sea Surface Height (l_obc_ogcm_rssh=.true.), Temperature (l_obc_ogcm_rt=.true.), Salinity ( l_obc_ogcm_rs=.true.), Barotropic Velocities (l_obc_ogcm_ruv=.true.), 3D Velocities (l_obc_ogcm_ruvz=.true.)

You can combine l_obc_tide=.true. and l_obc_ogcm=.true.

3. Specify which operator you want to use to apply the open boundary conditions (l_obc_mars=.true. or l_obc_diri=.true. or l_obc_char=.true.)

Other informations are available inside paraspec.txt and on pages 63-66 of mars_dvper_manual