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AMnet documentation
The AMnet HOWTO
All modules are shared libraries. Native modules can be loaded directly,
Java modules require a wrapper application (e.g. libwrapperJava.so)
and hardware modules need a wrapper as well (e.g. libwrapperHardware.so).
All modules (and wrappers) have to provide the following functions:
- char *initModule(char *initData, int *error)
-
Initializes and configures a module. If a problem with the
received data is encountered, an errorcode == NULL is returned.
Otherwise, the return value is a pointer to the global data,
a module requires. Warning: Modules are not allowed to specify
data of the form "int fd;". They have to move the data into
a configuration block and return its address on init. This
configuration block is passed together with every data block
to all functions as the last parameter "conf". Only exception:
The "run" function (see below).
- char *configure(char *paramType, char *paramName, char *paramValue, char *conf)
-
(Re)configures the module. The return value is a pointer to
the new configuration values ("conf" at all other function calls).
- int run(struct manage *data)
-
Processes all available data. If additional data is required
for processing, an error code has to be returned. The modules' own
global variables can be determined with the following function:
char *conf = getModuleConf(data);
- int shutdownModule(char *conf)
-
Switches the module off. All allocated resources have to be freed
now (e.g. the memory allocated for the configuration).
- int getStatus(char *conf)
-
Returns the status of the module.
The processing of Java modules is much easier. They are a standard class,
which has to provide the following functions:
- public int initModule(byte initData[])
- public void shutdownModule()
- public byte []run(byte data[])
- public void configure(byte confData[])
- public String getStatus()
These functions are similar to their C counterparts. In opposite to
the native C modules, Java modules can store their global data in
a much easier way, since these are instance variables and a separate
instance is created for every single class. Therefore, the handling
of confiuration pointers can be avoided.
In order to develop own modules, the user should make himself familiar
with the demo modules in the amnet/user/ee/src/modules
directory. pc.c is a very simple module, that counts the
packets in the input chain. This module can be used as an example for
storing global variables in a configuration block. A little more
complex example is the module mpeg.c, which can be used
together with a MPEG filter library to filter a MPEG stream. Two
aspects of this module are very important. First the module realizes a
buffer management, because the MPEG filter requires a minimal amount
of data in order to work. Secondly, this module shows how a module
with several parameters can be configured.
The compilation of user provided modules requires modification of the
Makefile in the directory amnet/user/ee.
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