source: rtems-docs/bsp_howto/ada95_interrupt.rst @ f916fca

Ada95 Interrupt Support
#######################

Introduction
============

This chapter describes what is required to enable Ada interrupt
and error exception handling when using GNAT over RTEMS.

The GNAT Ada95 interrupt support RTEMS was developed by
Jiri Gaisler <jgais@ws.estec.esa.nl> who also wrote this
chapter.

Mapping Interrupts to POSIX Signals
===================================

In Ada95, interrupts can be attached with the interrupt_attach pragma.
For most systems, the gnat run-time will use POSIX signal to implement
the interrupt handling, mapping one signal per interrupt. For interrupts
to be propagated to the attached Ada handler, the corresponding signal
must be raised when the interrupt occurs.

The same mechanism is used to generate Ada error exceptions.
Three error exceptions are defined: program, constraint and storage
error. These are generated by raising the predefined signals: SIGILL,
SIGFPE and SIGSEGV. These signals should be raised when a spurious
or erroneous trap occurs.

To enable gnat interrupt and error exception support for a particular
BSP, the following has to be done:

# Write an interrupt/trap handler that will raise the corresponding
  signal depending on the interrupt/trap number.

# Install the interrupt handler for all interrupts/traps that will be
  handled by gnat (including spurious).

# At startup, gnat calls ``__gnat_install_handler()``. The BSP
  must provide this function which installs the interrupt/trap handlers.

Which CPU-interrupt will generate which signal is implementation
defined. There are 32 POSIX signals (1 - 32), and all except the
three error signals (SIGILL, SIGFPE and SIGSEGV) can be used. I
would suggest to use the upper 16 (17 - 32) which do not
have an assigned POSIX name.

Note that the pragma interrupt_attach will only bind a signal
to a particular Ada handler - it will not unmask the
interrupt or do any other things to enable it. This have to be
done separately, typically by writing various device register.

Example Ada95 Interrupt Program
===============================

An example program (``irq_test``) is included in the
Ada examples package to show how interrupts can be handled
in Ada95. Note that generation of the test interrupt
(``irqforce.c``) is BSP specific and must be edited.

NOTE: The ``irq_test`` example was written for the SPARC/ERC32
BSP.

Version Requirements
====================

With RTEMS 4.0, a patch was required to psignal.c in RTEMS
sources (to correct a bug associated to the default action of
signals 15-32).   The SPARC/ERC32 RTEMS BSP includes the``gnatsupp`` subdirectory that can be used as an example
for other BSPs.

With GNAT 3.11p, a patch is required for ``a-init.c`` to invoke
the BSP specific routine that installs the exception handlers.

.. COMMENT: COPYRIGHT (c) 1988-2008.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.