J.7.1 Interrupt Entries
[Implementations are permitted to allow the attachment
of task entries to interrupts via the address clause. Such an entry is
referred to as an interrupt entry.
The address of the task entry corresponds to a hardware
interrupt in an implementation-defined manner. (See Ada.Interrupts.Reference
in
C.3.2.)]
Static Semantics
The following attribute
is defined:
For any task entry
X:
{interrupt
entry} X'
Address
For a task entry whose address is specified (an interrupt entry),
the value refers to the corresponding hardware interrupt. For such an
entry, as for any other task entry, the meaning of this value is implementation
defined. The value of this attribute is of the type of the subtype System.Address.
{specifiable
(of Address for entries) [partial]} Address
may be specified for single entries via an
attribute_definition_clause.
Dynamic Semantics
{initialization (of
a task object) [partial]} As part of the
initialization of a task object, the address clause for an interrupt
entry is elaborated[, which evaluates the
expression
of the address clause]. A check is made that the address specified is
associated with some interrupt to which a task entry may be attached.
{Program_Error (raised by failure of
run-time check)} If this check fails,
Program_Error is raised. Otherwise, the interrupt entry is attached to
the interrupt associated with the specified address.
{finalization (of
a task object) [partial]} Upon finalization
of the task object, the interrupt entry, if any, is detached from the
corresponding interrupt and the default treatment is restored.
While an interrupt entry is attached to an interrupt,
the interrupt is reserved (see
C.3).
An interrupt delivered to a task entry acts as a
call to the entry issued by a hardware task whose priority is in the
System.Interrupt_Priority range. It is implementation defined whether
the call is performed as an ordinary entry call, a timed entry call,
or a conditional entry call; which kind of call is performed can depend
on the specific interrupt.
Bounded (Run-Time) Errors
{bounded error (cause)
[partial]} It is a bounded error to evaluate
E'Caller (see
C.7.1) in an
accept_statement
for an interrupt entry. The possible effects are the same as for calling
Current_Task from an entry body.
Documentation Requirements
The implementation shall document to which interrupts
a task entry may be attached.
Documentation Requirement: The interrupts
to which a task entry may be attached.
The implementation shall document whether the invocation
of an interrupt entry has the effect of an ordinary entry call, conditional
call, or a timed call, and whether the effect varies in the presence
of pending interrupts.
Documentation Requirement: The type of
entry call invoked for an interrupt entry.
Implementation Permissions
The support for this subclause is optional.
Interrupts to which the implementation allows a task
entry to be attached may be designated as reserved for the entire duration
of program execution[; that is, not just when they have an interrupt
entry attached to them].
{
8652/0077}
{
AI95-00111-01}
Interrupt entry calls may be implemented by having the hardware execute
directly the appropriate
accept_statement.
Alternatively, the implementation is allowed to provide an internal interrupt
handler to simulate the effect of a normal task calling the entry.
The implementation is allowed to impose restrictions
on the specifications and bodies of tasks that have interrupt entries.
It is implementation defined whether direct calls
(from the program) to interrupt entries are allowed.
1 {
8652/0077}
{
AI95-00111-01}
Queued interrupts correspond to ordinary entry calls. Interrupts that
are lost if not immediately processed correspond to conditional entry
calls. It is a consequence of the priority rules that an
accept_statement
executed in response to an interrupt can be executed with the active
priority at which the hardware generates the interrupt, taking precedence
over lower priority tasks, without a scheduling action.
2 Control information that is supplied
upon an interrupt can be passed to an associated interrupt entry as one
or more parameters of mode in.
Examples
Example of an interrupt
entry:
task Interrupt_Handler is
entry Done;
for Done'Address use Ada.Interrupts.Reference(Ada.Interrupts.Names.Device_Done);
end Interrupt_Handler;
Wording Changes from Ada 83
{
AI95-00114-01}
RM83-13.5.1 did not adequately address the problems associated with interrupts.
This feature is now obsolescent and is replaced by the Ada 95 interrupt
model as specified in the Systems Programming Annex.
Wording Changes from Ada 95
Sponsored by Ada-Europe