Last modified 8 years ago Last modified on 11/12/12 15:03:55


Interfaces are used to store data in the BlackBoard and access it with (at most one) writer and (multiple) readers.

Creating new Interfaces

Interfaces are created using the interface generator. This generator requires an XML interface definition file and generates C++ and Lua source.

Required File Format

The interface is defined by an interface document specifying one <interface> element. It comprises (optional) constants, (mandatory) data fields, and (optional) messages.


<?xml version="1.0" encoding="UTF\-8"?>
<!DOCTYPE interface SYSTEM "interface.dtd">
<interface name="NameThisInterface" author="Author Name" year="2010">
  <!\-\- constant definitions \-\->
    <comment>Commentary on interface.</comment>
    <!\-\- field definitions \-\->
  <message name="MessageTypeName">
    <comment>Set the test int to the given value.</comment>
    <!\-\- reference and field definitions \-\->
  <!\-\- Any number of additional message types \-\->


The constants are optional. It comprises constant values of arbitrary types or enumerations.

<constant type="int32" value="5" name="CONSTANT_NAME">Comment</constant>

Constants are exported as static class members of the interface. The value of the field is a comment used for documentation purpose

<enum name="TestEnum">
  <comment>Demonstrating enums</comment>
  <item name="TEST_ENUM_1">Item 1</item>
  <item name="TEST_ENUM_2">Item 2</item>

Enumerations are symbolic names of type integer. The field text are comments about the overall enumeration and the enumeration items.


Data is stored in fields in the interfaces. Data can be one of the following types:

  • string
  • byte (equivalent to uint8)
  • char (equivalent to char)
  • int8
  • uint8
  • int16
  • uint16
  • int32
  • uint32
  • int64
  • uint64 (not recommended, see below)
  • bool
  • float
  • double
  • custom enum types (as specified in the constants)

Note that uint64 (and to some degree int64) can cause problems. Lua for example supports integers only up to 52 bits. Java does not support unsigned types, therefore it is limited to int64 (although not supported as of now, it may be in the future). If you think that you need 64 bit integers and need the full range, be aware of these problems and state this clearly in the documentation of the module in question.

Number and boolean types can be used to form statically sized arrays. For this add an attribute length with the number of elements in the array. The same attribute must be given for strings to denote the maximum length (including null termination).

<field type="bool" name="test_bool">Test Bool</field>
<field type="int32" name="test_int">Test integer</field>
<field type="string" length="30" name="test_string">A test string</field>
<field type="int32" length="30" name="test_array">Integer array</field>


Messages are defined as sub-documents. Any number of messages can be defined for an interface.

<message name="SetTestInt">
  <comment>Set the test int to the given value.</comment>
<message name="Calculate">
  <comment>Adds Summand and Addend.</comment>
  <field type="int32" name="summand">Summand</field>
  <field type="int32" name="addend">Addend</field>

The <ref> field can be used to reference fields of the interface. An appropriate field with the given name and the same type as in the interface is then added. Fields can otherwise be specified in the same way they are for the interface. References and fields can be mixed in a message.