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## 21. Customizing GENESIS

GENESIS was designed to be extensible. If you find that the objects provided by GENESIS do not serve your modeling needs, you can modify the functionality of existing objects, or create entirely new types. Likewise, you can extend the set of commands recognized by the SLI to include your own commands. You may do either of these within the GENESIS scripting language, by creating extended objects (see Extended Objects) and by defining script language functions.

However, there are occasions when you will need the computational efficiency and speed gained by compiling new object and command definitions into your own customized version of GENESIS. The speed advantage of using a compiled object instead of a script-defined extended object is most noticeable when it is necesssary to define a new PROCESS action, as this action will be performed at each simulation step. If the simulation requires many elements made from the object, then the setup time for the simulation may also be longer when using script-defined objects.

A GENESIS object is simply a particular C structure definition that is associated with a particular C function definition. Compiling these for use by GENESIS is equivalent to compiling a new library. When compiling new libraries into GENESIS, it is best to leave the ``official'' version of the genesis/src directory and its subdirectories unmodified. That way, you and other users will be able to create private customized versions of GENESIS, without changing the standard version. Typically, you will create a directory to contain your customized version of GENESIS, and one or more subdirectories to contain libraries for your new GENESIS commands and objects.

There are two main steps involved in creating a customized version of GENESIS which incorporates new commands or objects. First, one must create a library containing the the files which define the new commands or objects. Then, one or more libraries must be compiled into the new genesis executable. These two steps are described in Defining New Objects and Commands and Compiling a New Version of GENESIS.

## 21.1 Defining New Objects and Commands

If you have existing libraries, you may skip this section and go on to Compiling a New Version of GENESIS.

### Constructing the Library

The files in the Scripts/newlib directory illustrate the steps to follow in constructing a new GENESIS library:

1. Set up a directory to contain the new library and all of the code files to go into it. For example:

            mkdir newlib

   where 'newlib' will be the location of the new library. As described under Compiling a New Version of GENESIS, this directory should be created as a subdirectory of the one in which the new version of GENESIS will be compiled. The following steps refer to files which are created within this library directory.
2. Create an external header file. The example file example_ext.h contains the lines:

            #include "sim_ext.h"
            #include "example_struct.h"

   The file sim_ext.h is a specific GENESIS header file which must be included. It resides in the genesis/include directory, and includes several other files which make a number of necessary definitions. example_struct.h is a user-defined structure definition file which must be created.
3. Create the structure definition file. If new object functions are being added this file should be of the form

            #include "struct_defs.h"

            struct mystruct {
                TYPE
                fields ...
            };

            struct another_struct {
                TYPE
                other_fields ...
            };

            etc ...

   The structure names (e.g. mystruct) are arbitrary but must not conflict with any existing structure names. ``TYPE'' specifies a list of basic object fields. It should be selected from one those defined in genesis/include/struct_defs.h:

                ELEMENT_TYPE
                BUFFER_TYPE
                SEGMENT_TYPE
                CONNECTION_TYPE
                PROJECTION_TYPE
                CHAN_TYPE
                LINK_TYPE
                OUTPUT_TYPE

   These are macros which define a set of fields depending on the class of the object. The ``fields'' of the structure are additional fields that are completely user-defined. When writing a new object definition, you will pick one of the above types which most closely matches your needs and supplement it with any needed additional fields. For example, a new segment class object might have a structure definition like:

            struct mystruct {
                SEGMENT_TYPE
                float   state;
                int     count;
            };

   The newlib/example_struct.h structure file contains:

        #include "struct_defs.h"

        struct example_type {
            ELEMENT_TYPE
            float       input;
            float       output;
        };

   You can find other examples in the genesis/include directory. The documentation for each GENESIS object gives the name of the file which defines its data structure. If no new structure definitions are to be added, then simply create an empty structure file. This can be accomplished using the UNIX shell command

            touch "my_struct.h"

4. Create the files containing C code to define any new routines or objects. Your .c files should contain shell functions of the form:

            do_myfunc(argc,argv)
            int argc;
            char **argv;
            {
            }

   or object functions of the form

            MyObject(element,action)
            struct my_struct *element;
            Action *action;
            {
            }

   The names of these functions are arbitrary as long as they do not conflict with existing function names. If there is a conflict it will be reported during the link phase of compilation as a multiply defined function. In this case the function should be renamed. As a suggested convention, all shell functions should be prefixed with ``do_''. In the newlib directory, we have a separate file (command.c) for the new shell function (to become a new GENESIS routine) and another (example.c) for the new object function. These could have been combined into a single file, however. Note that the shell functions look like any normal C function, except that they must have two arguments, argc and argv, which will be used to get the actual arguments passed by the Script Language Interpreter. The file newlib/command.c illustrates a simple function which will be bound to a new GENESIS command which returns the number of arguments:

        #include "sim_ext.h"
        int do_example(argc,argv)
        int argc;
        char **argv;
        {
            printf("%d arguments passed to %s\n",argc,argv[0]);
            /*
            ** functions can return values which can be used in the interpreter
            */
            return(argc);
        }

   Note that it begins with a required inclusion of the definitions in sim_ext.h. Source files which define object functions must also include a header file giving structure declarations. example.c accomplishes this in a somewhat indirect way with the initial statement

           #include "example_ext.h"

   Thus, sim_ext.h is included, as was done with command.c, and an additional structure declaration file is also included, as described in step 3. The format for object functions is somewhat more complicated than that for shell functions. In the skeleton object function given above, the example function ``MyObject'' takes two arguments: (1) the pointer to the instantiation of the object structure (element) and (2) the pointer to the instantiation of the structure that specifies the action to be performed (action). Code which selects and implements the various actions which can be performed is given within the two curly brackets. The code for the example object ``ExampleObject'' is listed below in ``An Example Object Definition''. It has detailed comments explaining how to specify the actions performed and the way that messages are processed during the PROCESS action. The section on actions in Elements describes the actions which are common to many GENESIS objects. In general, the best way to write an object function is to begin by examining the source code for an existing object which is similar. The documentation for each object gives the name of the file and the name of the function which implements the object.
5. Create a library startup script. Once you have written functions to define new GENESIS shell commands or objects, you need to associate them with the command and object names which will be recognized by the SLI. This is done in a library startup script. The script is typically given a name of the form LIBRARY_NAMElib.g, where LIBRARY_NAME is the name of the library. For the example we have discussed so far, the script is called examplelib.g. Although the file name is given the extension ``.g'' (for historical reasons), this is not an ordinary script which may processed by GENESIS at run time. Instead, it is processed by during compilation by a program called ``code_g'', and it contains library startup commands which are not recognized as GENESIS commands, and are not listed by listcommands. The following startup commands (described in the GENESIS Startup Command Reference) are used in library startup scripts:

   Command | Description
   addfunc | Binds a compiled C function to the name of a GENESIS command.
   newclass | Adds a new class identifier to the list of object classes.
   object | Defines attributes of a GENESIS object and gives it a name.

   In addition, code_g recognizes the ordinary GENESIS command, addaction. This command is described under Extended Objects and in the GENESIS Command Reference section. In a library startup script, it is used to add a new action name to the list of GENESIS actions, and to associate a numerical value with it. This same numerical value is used in a case statement within the object function C code, in order to select the action to be performed. All four of these commands are illustrated in examplelib.g:

        addfunc example do_example int
        newclass        exampleclass
        addaction       NEWACTION       20
        object example_object example_type ExampleObject exampleclass device \
                -author         "M.Wilson Caltech 2/89" \
                -actions        RESET PROCESS NEWACTION \
                -messages       ADD 0           1 input \
                                SUBTRACT 1      1 input \
                                TWOARGS 2       2 arg1 arg2 \
                -readwrite input "Input variable, altered by ADD and SUBTRACT" \
                -readonly       output "Running total of input at each step" \
                -description    "exercise in creating new objects" \
                                "keeps a running sum of its inputs"

   The first line associates the command name ``example'' with the function do_example, defined in command.c. The optional argument for the data type (int) is needed here, because this routine returns an integer value. Next, a new class name (exampleclass) is defined, as well as a new action name and associated number. The final object command is continued over several lines. It is of the form:

            object name data_type function class [class] ... [options]

   Here, the new object will be given the name ``example_object''. In its defining function (ExampleObject) it was given a data structure of type ``example_type'', defined in step 3. The object may belong to more than one class. In this case, it is assigned to the newly defined exampleclass and to the pre-existing device class. It is required that any actions which the object performs be listed following the ```-actions`'' argument. The code in example.c gives the statements to be executed for the actions RESET, PROCESS, and NEWACTION. If messages are used by the object then the ```-message`'' option must be defined with the following arguments:
   1. the name of the message can be any string. This is used by the addmsg command. In this case, example.c defines ADD, SUBTRACT, and TWOARGS.
   2. the case number of the message type must correspond to the value defined in the code definition (see the MSGLOOP of example.c).
   3. the number of arguments to the message.
   4. the names of the arguments are arbitrary and are used for documenting purposes (there MUST be as many names as there are arguments).
   The names of the object fields (plus an optional descriptive string) are given with one of the options ```-readwrite`'', ```-readonly`'', or ```-hidden`''. These option names also give the protection that is assigned to the fields. In this case, we want to be able to set and inspect the input field. As the output field will be calculated by the object, it should be readable, but not writeable by the user. In other cases we may wish to use fields for internal calculations, but keep them hidden from the user. These are specified with the ```-hidden`'' option. The remaining fields are added for the purpose of documenting the object and are optional.
6. Create and Edit the library Makefile. The genesis directory in the GENESIS distribution (for example, /usr/genesis) contains a file Libmake that is used as a template for the Makefile. Copy it into the library directory, giving it the name Makefile. There will be a list of seven variables which must be set. These variables are:
   1. GENESIS should contain the name of the genesis system files. For example

                GENESIS            = /usr/genesis

      This is normally written into the Libmake file at the time GENESIS is installed. If GENESIS has been moved, or you are modifying libraries provided by someone else, you should check to be sure that the path is correct.
   2. LIBRARY_NAME is the name that you will use to refer to this library. It can be any name which does not conflict with existing libraries. For example using the specification in step 1:

               LIBRARY_NAME        = example

      The LIBRARY_NAME will also be entered in the 'liblist' file residing in the parent directory of the library directory, as decribed in Compiling a New Version of GENESIS.
   3. STARTUP is the name of the library startup script, described in step 4:

               STARTUP             = examplelib.g

   4. STRUCTURES is the name of the .h file containing the structure definitions created in step 2. Only one filename is allowed. For example:

               STRUCTURES          = example_struct.h

   5. EXT_HEADER is the name of the external header file created in step 1. Only one filename is allowed. For example:

               EXT_HEADER          = example_ext.h

   6. TARGET_OBJ is the name of the of the object file which will be created for the libarary. This should be called LIBRARY_NAMElib.o, where LIBRARY_NAME is the name of the library. For example, with the library ``example'', this would be:

               TARGET_OBJ          = examplelib.o

      This name (with the path to the library) is also used for the USERLIB variable in the Makefile (derived from Usermake) in the parent directory, as decribed in Compiling a New Version of GENESIS.
   7. OBJECTS is the list of object files (.o files) to be included in the new library. The names of these files should be the same as the source code (.c) files with the .c extension changed to .o. For example, with source code files command.c and example.c.

               OBJECTS             = command.o example.o

### An Example Object Definition

The file Scripts/newlib/example.c illustrates features which are common to the source code for many GENESIS object functions:

     #include "example_ext.h"

     #define ADD            0
     #define SUBTRACT       1
     #define TWOARGS        2
     #define NEWACTION      20

     /*
     ** example of how to define a new object function
     */
     /* M.Wilson Caltech 1/89 */
     /*
     ** The user can give the object function any unique name.
     ** Similarly, the arguments to the function can have arbitrary names.
     */
     ExampleObject(element,action)
     struct example_type *element;
     Action         *action;
     {
     /* If the element is to receive messages, this pointer (MsgIn *msg) must be
     ** declared.
     */
     MsgIn  *msg;
     double value;

         /*
         ** The debugging level can be assigned at runtime within the
         ** interpreter using the 'debug' command.  The function ActionHeader
         ** will cause GENESIS to print a standard message consisting
         ** of the name of the function called, the name of the element,
         ** and the name of the action being executed.
         */
         if(debug > 1){
             /* just prints out information which helps see what is happening */
             ActionHeader("ExampleObjectt",element,action);
         }

         SELECT_ACTION(action){
         /*
         ** SELECT_ACTION is a macro for a switch-case statement switching on the
         ** action requested.
         ** There are a number of predefined actions (see sim_defs.h)
         ** which are typically used by elements. PROCESS is one of them
         ** New actions can be added in any element. Use the 'addaction'
         ** command in the object definition script to inform the simulator
         ** of the new action. The case number asssigned to new actions
         ** is relatively arbitrary as long as it does not conflict with
         ** the case numbers of other actions defined in the element.
         ** (you should get a compiler error if there is a conflict).
         */
         case NEWACTION:
             printf("code for the new action\n");
             break;
         case PROCESS:
             element->input = 0;
             /*
             ** This is the way in which messages are processed
             ** MSGLOOP is a macro which scans all incoming messages and
             ** executes the code in the appropriate case statement
             ** depending on the message type
             **
             */
             MSGLOOP(element,msg) {
                 /*
                 ** The case number assigned here must be defined in the
                 ** in the message section of the object definition
                 ** (see examplelib.g)
                 */
                 case ADD:
                     /*
                     ** The function MSGVALUE allows you to access the contents
                     ** of the message arguments passed into the element.
                     ** The first argument is just the msg pointer,
                     ** the second argument is the argument number
                     ** Thus to get the first argument of a message use
                     ** MSGVALUE(msg,0). To get the second (assuming there are
                     ** more than one argument in the message) use
                     ** MSGVALUE(msg,1).
                     ** Note that the return type from
                     ** MSGVALUE is always type double
                     **
                     ** You are free to place whatever code you would like in here
                     */
                     value = MSGVALUE(msg,0);
                     element->input += value;
                     printf("adding a message value of %f\n",value);
                     break;
                 case SUBTRACT:
                     value = MSGVALUE(msg,0);
                     element->input -= value;
                     printf("subtracting a message value of %f\n",value);
                     break;
                 case TWOARGS:
                     printf("processing arguments %f and %f\n",
                             MSGVALUE(msg,0),MSGVALUE(msg,1));
                     break;
                 default:
                     printf("Unknown message\n");
                     break;
             }
             /*
             ** In this case we add the element field 'input' to 'output',
             ** using output to maintain a running sum.
             ** You are free to place whatever code you would like in here.
             */
             element->output += element->input;
             printf("element has been processed\n");
             break;
         /*
         ** The RESET action is used to return the element to a known
         ** initial state
         */
         case RESET:
             element->input = 0;
             element->output = 0;
             printf("element has been reset\n");
             break;
         }
     }

### 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 and Defining New Objects and Commands 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
               /* use Synapse_type if using normal synapses */
               struct MyWeirdSynapse_type *synapse;
               /* ... 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 GENESIS ) 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.

## 21.2 Compiling a New Version of GENESIS

To compile a new version of GENESIS containing new user libraries:

1. Create a directory from which to compile the new GENESIS. You may do this by using the UNIX `mkdir` command to create your own directory for containing the customized GENESIS.
2. You need new libraries to add. These will either be ones that you have created yourself, following the directions in Defining New Objects and Commands, or existing libraries which have been contributed by other GENESIS users. The Scripts/examples/newlib directory contains an example of a user-defined GENESIS library which you may use for testing these instructions. For now, we will assume that you have one or more library directories.
3. Create subdirectories for the libraries. The libraries should be contained in one or more subdirectories of the directory for the new GENESIS. If you have existing libraries, use either the UNIX `cp -r` (recursive copy) or `mv` command to put the library subdirectories under the directory which you created in the first step.
4. Create a ``Makefile'' for compiling GENESIS. The genesis directory in the GENESIS distribution contains a file ``Usermake'' that serves as a template for this Makefile. Copy it to the directory above those containing your libraries, giving it the name ``Makefile''. Please note that the Usermake file is subject to change with each GENESIS release. If there is potential that users with different versions of GENESIS will compile your library, provide a Makefile specific to each GENESIS release (e.g. Makefile2.2.1, Makefile2.3). At this point, your directory structure should look something like

                       new genesis  --> contains Makefile (from Usermake)
                             /\
                            /  \
                           /    \
                          /      \
                 new library     additional new
                 subdirectory    library subdirectories

   Each library subdirectory will contain its own Makefile constructed by editing genesis/Libmake, as described in the Libmake file and in Defining New Objects and Commands.
5. Edit the Makefile (copied from Usermake) as instructed by the comments in Makefile. First, there is a definition for the variable GENINST. The GENESIS installation process should create the Usermake file with this set to the full path of the genesis installation directory, for example:

            GENINST =       /usr/genesis

   If, for some reason, the GENESIS files have been moved from the original GENESIS installation directory, this line may need to be edited to reflect the change. Next, there are some instructions regarding assignment of the system-specific variables, MACHINE, OS, XLIB, CC, CFLAGS, CPP, LD, LINKFLAGS, and LEXLIB. These should be set to the same values as those used in the original genesis/src/Makefile when GENESIS was compiled. The following line,

            SIMNAME =       genesis

   gives the name of the GENESIS executable that will be produced. If you would like to give it another name like mygenesis to distinguish it from the standard version, you may change it here. Next, we come to the USERDIR variable. The instructions in the Makefile say that this should give the names of any library directories. If we were compiling the single library in the subdirectory newlib, we would say:

            USERDIR = newlib

   The variable USEROBJ should give the pathnames of any new library object modules. After compilation, each library will have a ``.o'' file which will be linked into GENESIS. The instructions in Usermake tell us that this name is specified by the TARGET_OBJ variable in the library Makefile. For the example given in Scripts/newlib, we would look in newlib/Makefile (the library Makefile) and see that it is set to examplelib.o. We need to give the path relative to the place where we are compiling the new GENESIS, so we would say:

           USEROBJ = newlib/examplelib.o

   The remaining variable to set is USERLIB, which should give the names of any new libraries. The library name is specified by the LIBRARY_NAME variable in the library Makefile. Following through with the newlib example, USERLIB would be set to

           USERLIB =example

   This completes the edits to the Makefile.
6. Check the contents of the libraries. If you have constructed the new libraries yourself, following the steps outlined in Defining New Objects and Commands, there should be little else to do. If you have received them from someone else, you should check the line in each library Makefile that begins with ```GENESIS =` ''. This should give the full path to the GENESIS distribution. If it is not where you keep your GENESIS distribution, change it accordingly.
7. Type ``make'' from within the directory containing the Usermake-derived Makefile. If you have compilation errors, it is time to carefully review the instructions! To delete the temporary files which were created during the compilation, type ``make clean''.
8. Test the new commands and objects. From within the directory in which you compiled the new genesis executable, type ``genesis''' (or ``./genesis'' if your path has been set by a particularly paranoid system manager). Now type ``listcommands'' and ``listobjects'' to see if the new commands and objects have really been incorporated. For the newlib example, you should find a new command called ``example'' and a new object called ``example_object''. Give GENESIS the command ```echo {example 1 2 3 4}`'' and see if the results are consistent with the comments in newlib/command.c. The command ```showobject example_object`'' should produce some information about the new object. You may execute the test script, newlib/testexample.g to see if elements created from this object behave as expected.

If you have problems running or compiling the new version of GENESIS, you should make sure that the files in genesis/lib were compiled under the same environment (operating system and compiler) as your new library. If you suspect that this is not the case, you should recompile GENESIS, following the instructions in genesis/src/README.

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