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12 >Configuration Items</TITLE
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65 >Chapter 24. CDL Concepts</TD
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85 NAME="CDL-CONFIGURATION-ITEMS">Configuration Items</H1
91 >Configuration items</I
94 individual entities that form a configuration. Each item
95 corresponds to the setting of a C pre-processor macro (for
99 >CYGHWR_HAL_ARM_PID_GDB_BAUD</TT
104 > itself is written to test such pre-processor
105 macros so as to tailor the code. User code can do
108 >Configuration items come in the following flavors:</P
120 >: such entities serve only as
121 place holders in the hierarchy, allowing other entities to be grouped
132 > entities are the most common
133 flavor; they correspond to units of functionality that can be either
134 enabled or disabled. If the entity is enabled then there will be
135 a #define; code will check the setting using, for example, #ifdef</P
145 > entities encapsulate some arbitrary
146 data. Other properties such as a set or range of legal values can
147 be used to constrain the actual values, for example to an integer
148 or floating point value within a certain range.</P
158 > entities combine the attributes
172 can be enabled or disabled and, if enabled, will hold a data value.</P
176 >Like packages, configuration items exist in a tree-based hierarchy:
177 each configuration item has a parent which may be another configuration
178 item or a package. Under some conditions (such as when packages
179 are added or removed from a configuration), items may be “re-parented” such
180 that their position in the tree changes. </P
186 NAME="AEN1898">Expressions</H2
188 >Expressions are relationships between CDL items. There are
189 three types of expression in CDL:</P
193 NAME="CDL-EXPRESSIONS"><P
195 >Table 24-1. CDL Expressions</B
214 HREF="cdl-configuration-items.html#TABLE-CONFIGURATION-PROPERTIES"
232 >legal_values property</TD
243 values (for example “1 to 10”)</TD
247 >legal_values property </TD
261 >requires and active_if properties</TD
272 NAME="AEN1923">Properties</H2
274 >Each configuration item has a set of properties. The following
275 table describes the most commonly used:</P
279 NAME="TABLE-CONFIGURATION-PROPERTIES"><P
281 >Table 24-2. Configuration properties</B
319 >The “type” of the item, as
331 the item is enabled </TD
341 >The current value of the item </TD
351 >An ordinary expression defining the default value of the
363 list expression defining the values the item may hold (for example,
375 goal expression denoting the requirement for this item to be active
393 expression denoting requirements this item places on others (see
411 the item as non-modifiable </TD
422 C pre-processor macro </TD
433 file in which the macro is defined </TD
444 a documentation page describing the item </TD
455 that a particular package is related to specific hardware</TD
461 >A complete description of properties is contained in the <I
464 Writer’s Guide</I
472 NAME="AEN1976">Inactive Items</H2
474 >Descendants of an item that is disabled are inactive: their
475 values may not be changed. Items may also become <SPAN
482 an active_if expression is used to make the item dependent
483 on an expression involving other items. </P
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