The Package Interrupts
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

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# C.3.2 The Package Interrupts

#### Static Semantics

1
The following language-defined packages exist:
2/3
with System;
with System.Multiprocessors;
package Ada.Interrupts is
type Interrupt_Id is implementation-defined;
type Parameterless_Handler is
access protected procedure;
3/1
This paragraph was deleted.
4
function Is_Reserved (Interrupt : Interrupt_Id)
return Boolean;
5
function Is_Attached (Interrupt : Interrupt_Id)
return Boolean;
6
function Current_Handler (Interrupt : Interrupt_Id)
return Parameterless_Handler;
7
procedure Attach_Handler
(New_Handler : in Parameterless_Handler;
Interrupt : in Interrupt_Id);
8
procedure Exchange_Handler
(Old_Handler : out Parameterless_Handler;
New_Handler : in Parameterless_Handler;
Interrupt : in Interrupt_Id);
9
procedure Detach_Handler
(Interrupt : in Interrupt_Id);
10
function Reference (Interrupt : Interrupt_Id)
return System.Address;
10.1/3
function Get_CPU (Interrupt : Interrupt_Id)
return System.Multiprocessors.CPU_Range;
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private
... -- not specified by the language
end Ada.Interrupts;
12
package Ada.Interrupts.Names is
implementation-defined : constant Interrupt_Id :=
implementation-defined;
. . .
implementation-defined : constant Interrupt_Id :=
implementation-defined;
end Ada.Interrupts.Names;

#### Dynamic Semantics

13
The Interrupt_Id type is an implementation-defined discrete type used to identify interrupts.
14
The Is_Reserved function returns True if and only if the specified interrupt is reserved.
15
The Is_Attached function returns True if and only if a user-specified interrupt handler is attached to the interrupt.
16/1
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 null.
17/3
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 null, the default treatment is restored. If New_Handler designates a protected procedure for which the aspect Interrupt_Handler is False, Program_Error is raised. In this case, the operation does not modify the existing interrupt treatment.
18/1
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. If the previous treatment is not a user-defined handler, null is returned.
19
The Detach_Handler procedure restores the default treatment for the specified interrupt.
20
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. Program_Error is raised if this check fails.
21/3
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 aspect Attach_Handler), the handler is not detached and Program_Error is raised.
22/2
The Reference function returns a value of type System.Address that can be used to attach a task entry via an address clause (see J.7.1) 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.
22.1/3
The function Get_CPU returns the processor on which the handler for Interrupt is executed. If the handler can execute on more than one processor the value System.Multiprocessors.Not_A_Specific_CPU is returned.

#### Implementation Requirements

23
At no time during attachment or exchange of handlers shall the current handler of the corresponding interrupt be undefined.

#### Documentation Requirements

24/3
If the Ceiling_Locking policy (see D.3) is in effect, the implementation shall document the default ceiling priority assigned to a protected object that contains a protected procedure that specifies either the Attach_Handler or Interrupt_Handler aspects, but does not specify the Interrupt_Priority aspect. This default need not be the same for all interrupts.

#### Implementation Advice

25
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.
NOTES
26
8 The package Interrupts.Names contains implementation-defined names (and constant values) for the interrupts that are supported by the implementation.

#### Examples

27
Example of interrupt handlers:
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Device_Priority : constant
array (1..5) of System.Interrupt_Priority := ( ... );
protected type Device_Interface
(Int_Id : Ada.Interrupts.Interrupt_Id)
with Interrupt_Priority => Device_Priority(Int_Id) is
procedure Handler
with Attach_Handler => Int_Id;
...
end Device_Interface;
...
Device_1_Driver : Device_Interface(1);
...
Device_5_Driver : Device_Interface(5);
...

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