Contents Index Search Previous Next
C.3.1 Protected Procedure Handlers
The form of
a pragma Interrupt_Handler is as
The form of
a pragma Attach_Handler is as follows:
Name Resolution Rules
For the Interrupt_Handler and Attach_Handler pragmas,
the handler_name shall resolve
to denote a protected procedure with a parameterless profile.
For the Attach_Handler pragma, the expected type
for the expression
The Attach_Handler pragma is only allowed immediately
within the protected_definition
where the corresponding subprogram is declared. The corresponding protected_type_declaration
shall be a library level declaration.
The Interrupt_Handler pragma is only allowed immediately
within a protected_definition. The
shall be a library level declaration. In addition, any object_declaration
of such a type shall be a library level declaration.
If the pragma Interrupt_Handler appears in a protected_definition
then the corresponding procedure can be attached dynamically, as a handler,
to interrupts (see C.3.2
). Such procedures
are allowed to be attached to multiple interrupts.
in the Attach_Handler pragma as evaluated at object creation time specifies
an interrupt. As part of the initialization of that object, if the Attach_Handler
pragma is specified, the handler
procedure is attached to the
is made that the corresponding interrupt is not reserved.
is raised if the check fails, and the existing treatment for the interrupt
is not affected.
the Ceiling_Locking policy (see D.3
) is in
effect then upon the initialization of a protected object that either
an Attach_Handler or Interrupt_Handler pragma applies to one of its procedures,
a check is made that the ceiling priority defined in the protected_definition
is in the range of System.Interrupt_Priority.
the check fails, Program_Error is raised.
When a protected object
is finalized, for any of its procedures that are attached to interrupts,
the handler is detached. If the handler was attached by a procedure in
the Interrupts package or if no user handler was previously attached
to the interrupt, the default treatment is restored. If an Attach_Handler
pragma was used and the most recently attached handler for the same interrupt
is the same as the one that was attached at the time the protected object
was initialized, the previous handler is restored.
When a handler is attached to an interrupt, the
interrupt is blocked (subject to the Implementation Permission in C.3
during the execution of every protected action on the protected object
containing the handler.
If the Ceiling_Locking policy
) is in effect and an interrupt is
delivered to a handler, and the interrupt hardware priority is higher
than the ceiling priority of the corresponding protected object, the
execution of the program is erroneous.
If the handlers for a
given interrupt attached via pragma Attach_Handler are not attached and
detached in a stack-like (LIFO) order, program execution is erroneous.
In particular, when a protected object is finalized, the execution is
erroneous if any of the procedures of the protected object are attached
to interrupts via pragma Attach_Handler and the most recently attached
handler for the same interrupt is not the same as the one that was attached
at the time the protected object was initialized.
The following metric
shall be documented by the implementation:
The worst case overhead for an interrupt handler that is a parameterless
protected procedure, in clock cycles. This is the execution time not
directly attributable to the handler procedure or the interrupted execution.
It is estimated as C - (A+B), where A is how long it takes to complete
a given sequence of instructions without any interrupt, B is how long
it takes to complete a normal call to a given protected procedure, and
C is how long it takes to complete the same sequence of instructions
when it is interrupted by one execution of the same procedure called
via an interrupt.
When the pragmas Attach_Handler or Interrupt_Handler
apply to a protected procedure, the implementation is allowed to impose
implementation-defined restrictions on the corresponding protected_type_declaration
An implementation may use a different mechanism
for invoking a protected procedure in response to a hardware interrupt
than is used for a call to that protected procedure from a task.
Notwithstanding what this
subclause says elsewhere, the Attach_Handler and Interrupt_Handler pragmas
are allowed to be used for other, implementation defined, forms of interrupt
Whenever possible, the implementation should
allow interrupt handlers to be called directly by the hardware.
Whenever practical, the implementation should
detect violations of any implementation-defined restrictions before run
4 The Attach_Handler pragma
can provide static attachment of handlers to interrupts if the implementation
supports preelaboration of protected objects. (See C.4.)
5 The ceiling priority
of a protected object that one of its procedures is attached to an interrupt
should be at least as high as the highest processor priority at which
that interrupt will ever be delivered.
6 Protected procedures
can also be attached dynamically to interrupts via operations declared
in the predefined package Interrupts.
7 An example of a possible
implementation-defined restriction is disallowing the use of the standard
storage pools within the body of a protected procedure that is an interrupt
Contents Index Search Previous Next Legal