CCustomBlock

Description

The CCustomBlock block provides a generic interface for specifying the block properties and defining the block simulation function. The simulation function is specified in C code and is stored as a block parameter. The code is compiled and used automatically at the start of the simulation.

Compared to creating and using new blocks, Custom blocks have the advantage of not requiring any library management operations. But even though their look and feel may be customized to some extent (in particular by encapsulating them in a masked Super Block) Custom blocks are not always the best solution. With Custom blocks, there is no mechanism for automatically upgrading the code of Custom blocks as there is for library blocks. Custom blocks are often used as a first step to develop and test C simulation codes destined for new blocks.

The CCustomBlock block also provide the option of not including the source code of the simulation function. The simulation function may be provided by a shared library. Instead of the C code, the block parameters include the path to the shared library and the name of the entry point. This option is particularly interesting for preserving intellectual property, but note that the model is no longer self-contained. The shared library file must be distributed along with the model.

Block Simulation Function

Block simulation functions are called by the Twin Activate simulator during simulation to perform different tasks, such as updating the output or the state. Simulation functions have two arguments: block and flag. The task to be realized is specified by the argument flag. The argument block is a the block’s data structure to be passed to the APIs to get and set block data.

Block Parameter GUI

CCustomBlock block's parameter GUIs provide an interactive user interface to define block properties. You can define the number and types of inputs and outputs, the states and simulation parameters and other properties. The interface also gives access to an editor for writing the block’s simulation code.

Developing a simulation code requires a knowledge of the APIs needed to get and set block data, for example for reading block inputs and writing block outputs. The CCustomBlock block provide a utility to generate a skeleton of the simulation code by taking into account the block properties specified by the user. This significantly facilitates the development of the simulation code.

Block inputs, outputs and simulation parameters are named and the code skeleton generator takes into account this information in order to provide a code where the user, in most cases, simply needs to add instructions involving the provided names as program variables. These variables are already declared and initialized when needed.

Alternative

The MathExpression and MatrixExpression blocks should be considered before using Custom blocks since they provide even simpler ways to express the dynamical behavior of a block. They are however limited to expressing stateless dynamics: block outputs depend on block inputs alone, and the expressions support a fixed set of functions that cannot be extended by the user.