Configuration items are the
individual entities that form a configuration. Each item
corresponds to the setting of a C pre-processor macro (for
The code of eCos itself is written to test such pre-processor
macros so as to tailor the code. User code can do
Configuration items come in the following flavors:
None: such entities serve only as
place holders in the hierarchy, allowing other entities to be grouped
Boolean entities are the most common
flavor; they correspond to units of functionality that can be either
enabled or disabled. If the entity is enabled then there will be
a #define; code will check the setting using, for example, #ifdef
Data entities encapsulate some arbitrary
data. Other properties such as a set or range of legal values can
be used to constrain the actual values, for example to an integer
or floating point value within a certain range.
Booldata entities combine the attributes
of Boolean and Data: they
can be enabled or disabled and, if enabled, will hold a data value.
Like packages, configuration items exist in a tree-based hierarchy:
each configuration item has a parent which may be another configuration
item or a package. Under some conditions (such as when packages
are added or removed from a configuration), items may be “re-parented” such
that their position in the tree changes.
Descendants of an item that is disabled are inactive: their
values may not be changed. Items may also become inactive if
an active_if expression is used to make the item dependent
on an expression involving other items.