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@c

@c  COPYRIGHT (c) 1988-2002.

@c  On-Line Applications Research Corporation (OAR).

@c  All rights reserved.

@c

@c  intr.t,v 1.21 2002/03/28 02:26:44 joel Exp

@c

@chapter Interrupt Manager

@section Introduction

Any real-time executive must provide a mechanism for

quick response to externally generated interrupts to satisfy the

critical time constraints of the application.  The interrupt

manager provides this mechanism for RTEMS.  This manager permits

quick interrupt response times by providing the critical ability

to alter task execution which allows a task to be preempted upon

exit from an ISR.  The interrupt manager includes the following

directive:

@itemize @bullet

@item @code{@value{DIRPREFIX}interrupt_catch} - Establish an ISR

@item @code{@value{DIRPREFIX}interrupt_disable} - Disable Interrupts

@item @code{@value{DIRPREFIX}interrupt_enable} - Enable Interrupts

@item @code{@value{DIRPREFIX}interrupt_flash} - Flash Interrupt

@item @code{@value{DIRPREFIX}interrupt_is_in_progress} - Is an ISR in Progress

@end itemize

@section Background

@subsection Processing an Interrupt

@cindex interrupt processing

The interrupt manager allows the application to

connect a function to a hardware interrupt vector.  When an

interrupt occurs, the processor will automatically vector to

RTEMS.  RTEMS saves and restores all registers which are not

preserved by the normal @value{LANGUAGE} calling convention

for the target

processor and invokes the user's ISR.  The user's ISR is

responsible for processing the interrupt, clearing the interrupt

if necessary, and device specific manipulation.

@findex rtems_vector_number

The @code{@value{DIRPREFIX}interrupt_catch}

directive connects a procedure to

an interrupt vector.  The vector number is managed using

the @code{@value{DIRPREFIX}vector_number} data type.

The interrupt service routine is assumed

to abide by these conventions and have a prototype similar to

the following:

@ifset is-C

@findex rtems_isr

@example

rtems_isr user_isr(

  rtems_vector_number vector

);

@end example

@end ifset

@ifset is-Ada

@example

procedure User_ISR (

  vector : in     RTEMS.Vector_Number

);

@end example

@end ifset

The vector number argument is provided by RTEMS to

allow the application to identify the interrupt source.  This

could be used to allow a single routine to service interrupts

from multiple instances of the same device.  For example, a

single routine could service interrupts from multiple serial

ports and use the vector number to identify which port requires

servicing.

To minimize the masking of lower or equal priority

level interrupts, the ISR should perform the minimum actions

required to service the interrupt.  Other non-essential actions

should be handled by application tasks.  Once the user's ISR has

completed, it returns control to the RTEMS interrupt manager

which will perform task dispatching and restore the registers

saved before the ISR was invoked.

The RTEMS interrupt manager guarantees that proper

task scheduling and dispatching are performed at the conclusion

of an ISR.  A system call made by the ISR may have readied a

task of higher priority than the interrupted task.  Therefore,

when the ISR completes, the postponed dispatch processing must

be performed.  No dispatch processing is performed as part of

directives which have been invoked by an ISR.

Applications must adhere to the following rule if

proper task scheduling and dispatching is to be performed:

@itemize @b{ }

@item @b{The interrupt manager must be used for all ISRs which

may be interrupted by the highest priority ISR which invokes an

RTEMS directive.}

@end itemize

Consider a processor which allows a numerically low

interrupt level to interrupt a numerically greater interrupt

level.  In this example, if an RTEMS directive is used in a

level 4 ISR, then all ISRs which execute at levels 0 through 4

must use the interrupt manager.

Interrupts are nested whenever an interrupt occurs

during the execution of another ISR.  RTEMS supports efficient

interrupt nesting by allowing the nested ISRs to terminate

without performing any dispatch processing.  Only when the

outermost ISR terminates will the postponed dispatching occur.

@subsection RTEMS Interrupt Levels

@cindex interrupt levels

Many processors support multiple interrupt levels or

priorities.  The exact number of interrupt levels is processor

dependent.  RTEMS internally supports 256 interrupt levels which

are mapped to the processor's interrupt levels.  For specific

information on the mapping between RTEMS and the target

processor's interrupt levels, refer to the Interrupt Processing

chapter of the Applications Supplement document for a specific

target processor.

@subsection Disabling of Interrupts by RTEMS

@cindex disabling interrupts

During the execution of directive calls, critical

sections of code may be executed.  When these sections are

encountered, RTEMS disables all maskable interrupts before the

execution of the section and restores them to the previous level

upon completion of the section.  RTEMS has been optimized to

insure that interrupts are disabled for a minimum length of

time.  The maximum length of time interrupts are disabled by

RTEMS is processor dependent and is detailed in the Timing

Specification chapter of the Applications Supplement document

for a specific target processor.

Non-maskable interrupts (NMI) cannot be disabled, and

ISRs which execute at this level MUST NEVER issue RTEMS system

calls.  If a directive is invoked, unpredictable results may

occur due to the inability of RTEMS to protect its critical

sections.  However, ISRs that make no system calls may safely

execute as non-maskable interrupts.

@section Operations

@subsection Establishing an ISR

The @code{@value{DIRPREFIX}interrupt_catch}

directive establishes an ISR for

the system.  The address of the ISR and its associated CPU

vector number are specified to this directive.  This directive

installs the RTEMS interrupt wrapper in the processor's

Interrupt Vector Table and the address of the user's ISR in the

RTEMS' Vector Table.  This directive returns the previous

contents of the specified vector in the RTEMS' Vector Table.

@subsection Directives Allowed from an ISR

Using the interrupt manager insures that RTEMS knows

when a directive is being called from an ISR.  The ISR may then

use system calls to synchronize itself with an application task.

The synchronization may involve messages, events or signals

being passed by the ISR to the desired task.  Directives invoked

by an ISR must operate only on objects which reside on the local

node.  The following is a list of RTEMS system calls that may be

made from an ISR:

@itemize @bullet

@item Task Management

@itemize -

@item task_get_note, task_set_note, task_suspend, task_resume

@end itemize

@item Clock Management

@itemize -

@item clock_get, clock_tick

@end itemize

@item Message, Event, and Signal Management

@itemize -

@item message_queue_send, message_queue_urgent

@item event_send

@item signal_send

@end itemize

@item Semaphore Management

@itemize -

@item semaphore_release

@end itemize

@item Dual-Ported Memory Management

@itemize -

@item port_external_to_internal, port_internal_to_external

@end itemize

@item IO Management

@itemize -

@item io_initialize, io_open, io_close, io_read, io_write, io_control

@end itemize

@item Fatal Error Management

@itemize -

@item fatal_error_occurred

@end itemize

@item Multiprocessing

@itemize -

@item multiprocessing_announce

@end itemize

@end itemize

@section Directives

This section details the interrupt manager's

directives.  A subsection is dedicated to each of this manager's

directives and describes the calling sequence, related

constants, usage, and status codes.

@c

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@page

@subsection INTERRUPT_CATCH - Establish an ISR

@cindex establish an ISR

@cindex install an ISR

@subheading CALLING SEQUENCE:

@ifset is-C

@findex rtems_interrupt_catch

@example

rtems_status_code rtems_interrupt_catch(

  rtems_isr_entry      new_isr_handler,

  rtems_vector_number  vector,

  rtems_isr_entry     *old_isr_handler

);

@end example

@end ifset

@ifset is-Ada

@example

procedure Interrupt_Catch (

   New_ISR_handler : in     RTEMS.Address;

   Vector          : in     RTEMS.Vector_Number;

   Old_ISR_Handler :    out RTEMS.Address;

   Result          :    out RTEMS.Status_Codes

);

@end example

@end ifset

@subheading DIRECTIVE STATUS CODES:

@code{@value{RPREFIX}SUCCESSFUL} - ISR established successfully@*

@code{@value{RPREFIX}INVALID_NUMBER} - illegal vector number@*

@code{@value{RPREFIX}INVALID_ADDRESS} - illegal ISR entry point or invalid @code{old_isr_handler}

@subheading DESCRIPTION:

This directive establishes an interrupt service

routine (ISR) for the specified interrupt vector number.  The

@code{new_isr_handler} parameter specifies the entry point of the ISR.

The entry point of the previous ISR for the specified vector is

returned in @code{old_isr_handler}.

To release an interrupt vector, pass the old handler's address obtained

when the vector was first capture.

@subheading NOTES:

This directive will not cause the calling task to be preempted.

@c

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@page

@subsection INTERRUPT_DISABLE - Disable Interrupts

@cindex disable interrupts

@subheading CALLING SEQUENCE:

@ifset is-C

@findex rtems_interrupt_disable

@example

void rtems_interrupt_disable(

  rtems_interrupt_level  level

);

/* this is implemented as a macro and sets level as a side-effect */

@end example

@end ifset

@ifset is-Ada

@example

function Interrupt_Disable

return RTEMS.ISR_Level;

@end example

@end ifset

@subheading DIRECTIVE STATUS CODES:

NONE

@subheading DESCRIPTION:

This directive disables all maskable interrupts and returns

the previous @code{level}.  A later invocation of the

@code{@value{DIRPREFIX}interrupt_enable} directive should be used to

restore the interrupt level.

@subheading NOTES:

This directive will not cause the calling task to be preempted.

@ifset is-C

@b{This directive is implemented as a macro which modifies the @code{level}

parameter.}

@end ifset

@c

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@page

@subsection INTERRUPT_ENABLE - Enable Interrupts

@cindex enable interrupts

@subheading CALLING SEQUENCE:

@ifset is-C

@findex rtems_interrupt_enable

@example

void rtems_interrupt_enable(

  rtems_interrupt_level  level

);

@end example

@end ifset

@ifset is-Ada

@example

procedure Interrupt_Enable (

   Level : in     RTEMS.ISR_Level

);

@end example

@end ifset

@subheading DIRECTIVE STATUS CODES:

NONE

@subheading DESCRIPTION:

This directive enables maskable interrupts to the @code{level}

which was returned by a previous call to

@code{@value{DIRPREFIX}interrupt_disable}.

Immediately prior to invoking this directive, maskable interrupts should

be disabled by a call to @code{@value{DIRPREFIX}interrupt_disable}

and will be enabled when this directive returns to the caller.

@subheading NOTES:

This directive will not cause the calling task to be preempted.

@c

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@page

@subsection INTERRUPT_FLASH - Flash Interrupts

@cindex flash interrupts

@subheading CALLING SEQUENCE:

@ifset is-C

@findex rtems_interrupt_flash

@example

void rtems_interrupt_flash(

  rtems_interrupt_level level

);

@end example

@end ifset

@ifset is-Ada

@example

procedure Interrupt_Flash (

   Level : in     RTEMS.ISR_Level

);

@end example

@end ifset

@subheading DIRECTIVE STATUS CODES:

NONE

@subheading DESCRIPTION:

This directive temporarily enables maskable interrupts to the @code{level}

which was returned by a previous call to

@code{@value{DIRPREFIX}interrupt_disable}.

Immediately prior to invoking this directive, maskable interrupts should

be disabled by a call to @code{@value{DIRPREFIX}interrupt_disable}

and will be redisabled when this directive returns to the caller.

@subheading NOTES:

This directive will not cause the calling task to be preempted.

@c

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@page

@subsection INTERRUPT_IS_IN_PROGRESS - Is an ISR in Progress

@cindex is interrupt in progress

@subheading CALLING SEQUENCE:

@ifset is-C

@findex rtems_interrupt_is_in_progress

@example

rtems_boolean rtems_interrupt_is_in_progress( void );

@end example

@end ifset

@ifset is-Ada

@example

function Interrupt_Is_In_Progress

return RTEMS.Boolean;

@end example

@end ifset

@subheading DIRECTIVE STATUS CODES:

NONE

@subheading DESCRIPTION:

This directive returns @code{TRUE} if the processor is currently

servicing an interrupt and @code{FALSE} otherwise.  A return value

of @code{TRUE} indicates that the caller is an interrupt service

routine, @b{NOT} a task.  The directives available to an interrupt

service routine are restricted.

@subheading NOTES:

This directive will not cause the calling task to be preempted.