C.3.2 The Package Interrupts

The following language-defined packages exist: 

The Interrupt_Id type is an implementation-defined discrete type used to identify interrupts.

The Is_Reserved function returns True if and only if the specified interrupt is reserved.

The Is_Attached function returns True if and only if a user-specified interrupt handler is attached to the interrupt.

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.

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.

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. 

The Detach_Handler procedure restores the default treatment for the specified interrupt.

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.

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.

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.

  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.

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

The implementation shall document, when the Ceiling_Locking policy (see D.3) is in effect, 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 can be different for different interrupts. 

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.

Example of interrupt handlers: