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@chapter Ada95 Interrupt Support

@section 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  who also wrote this

chapter.

@section 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:

@enumerate

@item Write an interrupt/trap handler that will raise the corresponding

signal depending on the interrupt/trap number.

@item Install the interrupt handler for all interrupts/traps that will be

handled by gnat (including spurious).

@item At startup, gnat calls @code{__gnat_install_handler()}. The bsp

must provide this function which installs the interrupt/trap handlers.

@end enumerate

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.

@section Example Ada95 Interrupt Program

An example program (@code{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

(@code{irqforce.c}) is bsp specific and must be edited.

NOTE: The @code{irq_test} example was written for the SPARC/ERC32

BSP.

@section 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

@code{gnatsupp} subdirectory that can be used as an example

for other BSPs.

With GNAT 3.11p, a patch is required for @code{a-init.c} to invoke

the BSP specific routine that installs the exception handlers.