20.1.3
Creating New Synaptic Objects
We anticipate that many GENESIS users will want to write variants of the
synchan and hebbsynchan objects to handle different kinds of
synaptically-mediated behavior. Currently, this means that one has to
write a
C function defining the object, usually in a user library. See
``Customizing
GENESIS'' (Customizing.doc) and ``Defining New Objects and Commands''
(NewObjects.doc) for more information on this.
In general, one should start by copying an existing object that is as
close to
the desired object as possible and then modifying it. These
modifications may
involve adding new fields or deleting old ones. In order to guarantee
that
the existing genesis commands for setting up synaptic connections work
properly with the new objects (e.g. planarconnect, volumeconnect,
planar/volumeweight, planar/volumedelay, etc.) we ask that aspiring
synchan
hackers obey the following guidelines:
1) The structure definition for the new object should be of the following
form:
struct MyWeirdSynchan_type
{
SYNCHAN_TYPE
struct MyWeirdSynapse_type *synapse; /* use Synapse_type if using
normal synapses */
/* ... put extra fields here if needed ... */
};
2) Some new kinds of synchans will have their own kinds of synapses with
extra fields not found in the standard synapses. The way to define
these is as follows:
struct MyWeirdSynapse_type
{
SYNAPSE_TYPE
/* ... put extra fields here if needed ... */
};
typedef struct MyWeirdSynapse_type MyWeirdSynapse;
An example of both (1) and (2) is in src/newconn/newconn_struct.h, with
the
definition of HebbSynchan_type and HebbSynapse_type. If your synapses
are
the same as previously-defined ones, then this step isn't necessary.
3) You must have code like this in the CREATE action of your synchan
type:
...
SELECT_ACTION(action)
{
case CREATE:
channel->synapse_size = (unsigned short) ( sizeof( MyWeirdSynapse )
);
channel->synapse = NULL; /* no synapses to start with */
break;
...
Note that all you have to do is change the word "Synapse" in synchan.c to
"MyWeirdSynapse".
4) In your <library_name>_ext.h file (see Customizing.doc) you must
include
(at least) the following:
#include "newconn_struct.h"
#include "synaptic_event.h"
extern void RemovePendingSynapticEvents();
/* and for hebbsynchan derivatives: */
#include "seg_struct.h"
/* for compartment definition */
If all this is done, and your code is correct, the new objects should
work
with the existing connection and weight/delay-setting functions in the
same
way as synchan and hebbsynchan do.