@c @c COPYRIGHT (c) 1988-2002. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @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 @c @c @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 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. @ifset is-C Passing a NULL pointer as the @code{old_handler} address and this parameter will be ignored. @end ifset @subheading NOTES: This directive will not cause the calling task to be preempted. @c @c @c @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 @c @c @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 @c @c @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 @c @c @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.