source: rtems-docs/ada_user/interrupt_manager.rst @ 4783b0d

4.11
Last change on this file since 4783b0d was 4783b0d, checked in by Amar Takhar <amar@…>, on Jan 17, 2016 at 4:37:28 PM

Split document into seperate files by section.

  • Property mode set to 100644
File size: 15.9 KB

Interrupt Manager

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:

  • rtems.interrupt_catch - Establish an ISR
  • rtems.interrupt_disable - Disable Interrupts
  • rtems.interrupt_enable - Enable Interrupts
  • rtems.interrupt_flash - Flash Interrupt
  • rtems.interrupt_local_disable - Disable Interrupts on Current Processor
  • rtems.interrupt_local_enable - Enable Interrupts on Current Processor
  • rtems.interrupt_lock_initialize - Initialize an ISR Lock
  • rtems.interrupt_lock_acquire - Acquire an ISR Lock
  • rtems.interrupt_lock_release - Release an ISR Lock
  • rtems.interrupt_lock_acquire_isr - Acquire an ISR Lock from ISR
  • rtems.interrupt_lock_release_isr - Release an ISR Lock from ISR
  • rtems.interrupt_is_in_progress - Is an ISR in Progress

Background

Processing an Interrupt

?
.. index:: 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 Ada 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... index:: rtems_vector_number

The rtems.interrupt_catch directive connects a procedure to an interrupt vector. The vector number is managed using the rtems.vector_number data type.

The interrupt service routine is assumed to abide by these conventions and have a prototype similar to the following:

NOT SUPPORTED FROM Ada BINDING

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:

  • ** The interrupt manager must be used for all ISRs which may be interrupted by the highest priority ISR which invokes an RTEMS directive.

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.

RTEMS Interrupt Levels

?
.. index:: 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.

Disabling of Interrupts by RTEMS

?
.. index:: 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 ensure 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.

Operations

Establishing an ISR

The rtems.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.

Directives Allowed from an ISR

Using the interrupt manager ensures 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:

  • Task Management Although it is acceptable to operate on the RTEMS_SELF task (e.g. the currently executing task), while in an ISR, this will refer to the interrupted task. Most of the time, it is an application implementation error to use RTEMS_SELF from an ISR. - rtems_task_suspend - rtems_task_resume
  • Interrupt Management - rtems_interrupt_enable - rtems_interrupt_disable - rtems_interrupt_flash - rtems_interrupt_lock_acquire - rtems_interrupt_lock_release - rtems_interrupt_lock_acquire_isr - rtems_interrupt_lock_release_isr - rtems_interrupt_is_in_progress - rtems_interrupt_catch
  • Clock Management - rtems_clock_set - rtems_clock_get - rtems_clock_get_tod - rtems_clock_get_tod_timeval - rtems_clock_get_seconds_since_epoch - rtems_clock_get_ticks_per_second - rtems_clock_get_ticks_since_boot - rtems_clock_get_uptime - rtems_clock_set_nanoseconds_extension - rtems_clock_tick
  • Timer Management - rtems_timer_cancel - rtems_timer_reset - rtems_timer_fire_after - rtems_timer_fire_when - rtems_timer_server_fire_after - rtems_timer_server_fire_when
  • Event Management - rtems_event_send - rtems_event_system_send - rtems_event_transient_send
  • Semaphore Management - rtems_semaphore_release
  • Message Management - rtems_message_queue_send - rtems_message_queue_urgent
  • Signal Management - rtems_signal_send
  • Dual-Ported Memory Management - rtems_port_external_to_internal - rtems_port_internal_to_external
  • IO Management The following services are safe to call from an ISR if and only if the device driver service invoked is also safe. The IO Manager itself is safe but the invoked driver entry point may or may not be. - rtems_io_initialize - rtems_io_open - rtems_io_close - rtems_io_read - rtems_io_write - rtems_io_control
  • Fatal Error Management - rtems_fatal - rtems_fatal_error_occurred
  • Multiprocessing - rtems_multiprocessing_announce

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.

INTERRUPT_CATCH - Establish an ISR

?
.. index:: establish an ISR
?
.. index:: install an ISR

CALLING SEQUENCE:

NOT SUPPORTED FROM Ada BINDING

DIRECTIVE STATUS CODES:

RTEMS.SUCCESSFUL - ISR established successfully RTEMS.INVALID_NUMBER - illegal vector number RTEMS.INVALID_ADDRESS - illegal ISR entry point or invalid old_isr_handler

DESCRIPTION:

This directive establishes an interrupt service routine (ISR) for the specified interrupt vector number. The``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 old_isr_handler.

To release an interrupt vector, pass the old handler’s address obtained when the vector was first capture.

NOTES:

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

INTERRUPT_DISABLE - Disable Interrupts

?
.. index:: disable interrupts

CALLING SEQUENCE:

function Interrupt_Disable return RTEMS.ISR_Level;

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive disables all maskable interrupts and returns the previous level. A later invocation of the``rtems.interrupt_enable`` directive should be used to restore the interrupt level.

NOTES:

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

This directive is only available on uni-processor configurations. The directive rtems.interrupt_local_disable is available on all configurations.

INTERRUPT_ENABLE - Enable Interrupts

?
.. index:: enable interrupts

CALLING SEQUENCE:

procedure Interrupt_Enable (
Level : in     RTEMS.ISR_Level
);

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive enables maskable interrupts to the level which was returned by a previous call to``rtems.interrupt_disable``. Immediately prior to invoking this directive, maskable interrupts should be disabled by a call to rtems.interrupt_disable and will be enabled when this directive returns to the caller.

NOTES:

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

This directive is only available on uni-processor configurations. The directive rtems.interrupt_local_enable is available on all configurations.

INTERRUPT_FLASH - Flash Interrupts

?
.. index:: flash interrupts

CALLING SEQUENCE:

procedure Interrupt_Flash (
Level : in     RTEMS.ISR_Level
);

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive temporarily enables maskable interrupts to the level which was returned by a previous call to``rtems.interrupt_disable``. Immediately prior to invoking this directive, maskable interrupts should be disabled by a call to rtems.interrupt_disable and will be redisabled when this directive returns to the caller.

NOTES:

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

This directive is only available on uni-processor configurations. The directives rtems.interrupt_local_disable and``rtems.interrupt_local_enable`` is available on all configurations.

INTERRUPT_LOCAL_DISABLE - Disable Interrupts on Current Processor

?
.. index:: disable interrupts

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive disables all maskable interrupts and returns the previous level. A later invocation of the``rtems.interrupt_local_enable`` directive should be used to restore the interrupt level.

NOTES:

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

On SMP configurations this will not ensure system wide mutual exclusion. Use interrupt locks instead.

INTERRUPT_LOCAL_ENABLE - Enable Interrupts on Current Processor

?
.. index:: enable interrupts

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive enables maskable interrupts to the level which was returned by a previous call to``rtems.interrupt_local_disable``. Immediately prior to invoking this directive, maskable interrupts should be disabled by a call to rtems.interrupt_local_disable and will be enabled when this directive returns to the caller.

NOTES:

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

INTERRUPT_LOCK_INITIALIZE - Initialize an ISR Lock

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

Initializes an interrupt lock.

NOTES:

Concurrent initialization leads to unpredictable results.

INTERRUPT_LOCK_ACQUIRE - Acquire an ISR Lock

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

Interrupts will be disabled. On SMP configurations this directive acquires a SMP lock.

NOTES:

This directive will not cause the calling thread to be preempted. This directive can be used in thread and interrupt context.

INTERRUPT_LOCK_RELEASE - Release an ISR Lock

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

The interrupt status will be restored. On SMP configurations this directive releases a SMP lock.

NOTES:

This directive will not cause the calling thread to be preempted. This directive can be used in thread and interrupt context.

INTERRUPT_LOCK_ACQUIRE_ISR - Acquire an ISR Lock from ISR

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

The interrupt status will remain unchanged. On SMP configurations this directive acquires a SMP lock.

In case the corresponding interrupt service routine can be interrupted by higher priority interrupts and these interrupts enter the critical section protected by this lock, then the result is unpredictable.

NOTES:

This directive should be called from the corresponding interrupt service routine.

INTERRUPT_LOCK_RELEASE_ISR - Release an ISR Lock from ISR

CALLING SEQUENCE:

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

The interrupt status will remain unchanged. On SMP configurations this directive releases a SMP lock.

NOTES:

This directive should be called from the corresponding interrupt service routine.

INTERRUPT_IS_IN_PROGRESS - Is an ISR in Progress

?
.. index:: is interrupt in progress

CALLING SEQUENCE:

function Interrupt_Is_In_Progress return RTEMS.Boolean;

DIRECTIVE STATUS CODES:

NONE

DESCRIPTION:

This directive returns TRUE if the processor is currently servicing an interrupt and FALSE otherwise. A return value of TRUE indicates that the caller is an interrupt service routine, NOT a task. The directives available to an interrupt service routine are restricted.

NOTES:

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

Note: See TracBrowser for help on using the repository browser.