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+.. SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)
+
+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_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
+
+- 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_broadcast
+  - 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