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<H1> C.3.2 The Package Interrupts</H1>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The following language-defined
packages exist: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Examples"><TT><B>with</B> System;<A NAME="I6659"></A><A NAME="I6660"></A><A NAME="I6661"></A><BR>
<B>package</B> Ada.Interrupts <B>is</B><BR>
<B>type</B> <A NAME="I6662"></A><A NAME="I6663"></A>Interrupt_ID <B>is</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I6664"></A><A NAME="I6665"></A>Parameterless_Handler <B>is</B><BR>
<B>access</B> <B>protected</B> <B>procedure</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3/1</FONT></DIV>
<DIV Class="Examples"><TT><FONT SIZE=-1><I>This paragraph was deleted.</I></FONT><S> </S></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6666"></A><A NAME="I6667"></A>Is_Reserved (Interrupt : Interrupt_ID)<BR>
<B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6668"></A><A NAME="I6669"></A>Is_Attached (Interrupt : Interrupt_ID)<BR>
<B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6670"></A><A NAME="I6671"></A>Current_Handler (Interrupt : Interrupt_ID)<BR>
<B>return</B> Parameterless_Handler;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6672"></A><A NAME="I6673"></A>Attach_Handler<BR>
(New_Handler : <B>in</B> Parameterless_Handler;<BR>
Interrupt : <B>in</B> Interrupt_ID);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6674"></A><A NAME="I6675"></A>Exchange_Handler<BR>
(Old_Handler : <B>out</B> Parameterless_Handler;<BR>
New_Handler : <B>in</B> Parameterless_Handler;<BR>
Interrupt : <B>in</B> Interrupt_ID);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6676"></A><A NAME="I6677"></A>Detach_Handler<BR>
(Interrupt : <B>in</B> Interrupt_ID);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6678"></A><A NAME="I6679"></A>Reference(Interrupt : Interrupt_ID)<BR>
<B>return</B> System.Address;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Examples"><TT><B>private</B><BR>
... -- <I>not specified by the language</I><BR>
<B>end</B> Ada.Interrupts;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> Ada.Interrupts.Names <B>is</B><A NAME="I6680"></A><A NAME="I6681"></A><A NAME="I6682"></A><BR>
<I>implementation-defined</I> : <B>constant</B> Interrupt_ID :=<BR>
<I>implementation-defined</I>;<BR>
. . .<BR>
<I>implementation-defined</I> : <B>constant</B> Interrupt_ID :=<BR>
<I>implementation-defined</I>;<BR>
<B>end</B> Ada.Interrupts.Names;</TT></DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal"> The Interrupt_ID type is an implementation-defined
discrete type used to identify interrupts.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Normal"> The Is_Reserved function returns True if and
only if the specified interrupt is reserved.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Normal"> The Is_Attached function returns True if and
only if a user-specified interrupt handler is attached to the interrupt.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0069">8652/0069</A></I>}
The Current_Handler function returns a value that represents the attached
handler of the interrupt. If no user-defined handler is attached to the
interrupt, Current_Handler returns <U><B>null</B></U><S>a value that
designates the default treatment; calling Attach_Handler or Exchange_Handler
with this value restores the default treatment</S>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal"> The Attach_Handler procedure attaches the specified
handler to the interrupt, overriding any existing treatment (including
a user handler) in effect for that interrupt. If New_Handler is <B>null</B>,
the default treatment is restored. <A NAME="I6683"></A>If New_Handler
designates a protected procedure to which the pragma Interrupt_Handler
does not apply, Program_Error is raised. In this case, the operation
does not modify the existing interrupt treatment.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0069">8652/0069</A></I>}
The Exchange_Handler procedure operates in the same manner as Attach_Handler
with the addition that the value returned in Old_Handler designates the
previous treatment for the specified interrupt.<U> If the previous treatment
is not a user-defined handler, <B>null</B> is returned.</U> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Calling Attach_Handler
or Exchange_Handler with this value for New_Handler restores the previous
handler.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>{<I><A HREF="defect1.html#8652/0069">8652/0069</A></I>}
<U>If the application uses only parameterless procedures as handlers
(other types of handlers may be provided by the implementation, but are
not required by the standard), then if Old_Handler is not <B>null</B>,
it may be called to execute the previous handler. This provides a way
to cascade application interrupt handlers. However, the default handler
cannot be cascaded this way (Old_Handler must be <B>null</B> for the
default handler).</U> </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Normal"> The Detach_Handler procedure restores the default
treatment for the specified interrupt.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Normal"> For all operations defined in this package that
take a parameter of type Interrupt_ID, with the exception of Is_Reserved
and Reference, a check is made that the specified interrupt is not reserved.
<A NAME="I6684"></A>Program_Error is raised if this check fails.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Normal"> If, by using the Attach_Handler, Detach_Handler,
or Exchange_Handler procedures, an attempt is made to detach a handler
that was attached statically (using the pragma Attach_Handler), the handler
is not detached and Program_Error is raised. <A NAME="I6685"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Normal"> The Reference function returns a value of type
System.Address that can be used to attach a task entry, via an address
clause (see <A HREF="AA-J-7-1.html">J.7.1</A>) to the interrupt specified
by Interrupt. This function raises Program_Error if attaching task entries
to interrupts (or to this particular interrupt) is not supported. <A NAME="I6686"></A></DIV>
<H4 ALIGN=CENTER>Implementation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Normal"> At no time during attachment or exchange of handlers
shall the current handler of the corresponding interrupt be undefined.</DIV>
<H4 ALIGN=CENTER>Documentation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Normal"> If the Ceiling_Locking policy (see <A HREF="AA-D-3.html">D.3</A>)
is in effect the implementation shall document the default ceiling priority
assigned to a protected object that contains either the Attach_Handler
or Interrupt_Handler pragmas, but not the Interrupt_Priority pragma.
[This default need not be the same for all interrupts.]</DIV>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>25</FONT></DIV>
<DIV Class="Normal"> If implementation-defined forms of interrupt
handler procedures are supported, such as protected procedures with parameters,
then for each such form of a handler, a type analogous to Parameterless_Handler
should be specified in a child package of Interrupts, with the same operations
as in the predefined package Interrupts.</DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>8 The package Interrupts.Names
contains implementation-defined names (and constant values) for the interrupts
that are supported by the implementation.</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>27</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Example of interrupt
handlers:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>28</FONT></DIV>
<DIV Class="Examples"><TT>Device_Priority : <B>constant</B><BR>
<B>array</B> (1..5) of System.Interrupt_Priority := ( ... );<BR>
<B>protected</B> <B>type</B> Device_Interface<BR>
(Int_ID : Ada.Interrupts.Interrupt_ID) <B>is</B><BR>
<B>procedure</B> Handler;<BR>
<B>pragma</B> Attach_Handler(Handler, Int_ID);<BR>
...<BR>
<B>pragma</B> Interrupt_Priority(Device_Priority(Int_ID));<BR>
<B>end</B> Device_Interface;<BR>
...<BR>
Device_1_Driver : Device_Interface(1);<BR>
...<BR>
Device_5_Driver : Device_Interface(5);<BR>
...</TT></DIV>
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