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-.. comment SPDX-License-Identifier: CC-BY-SA-4.0
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-.. COMMENT: All rights reserved.
-
-Port Specific Information
-#########################
-
-This chaper provides a general description of the type of architecture specific
-information which is in each of the architecture specific chapters that follow.
-The outline of this chapter is identical to that of the architecture specific
-chapters.
-
-In each of the architecture specific chapters, this introductory section will
-provide an overview of the architecture:
-
-**Architecture Documents**
-
-In each of the architecture specific chapters, this section will provide
-pointers on where to obtain documentation.
-
-CPU Model Dependent Features
-============================
-
-Microprocessors are generally classified into families with a variety of CPU
-models or implementations within that family.  Within a processor family, there
-is a high level of binary compatibility.  This family may be based on either an
-architectural specification or on maintaining compatibility with a popular
-processor.  Recent microprocessor families such as the SPARC or PowerPC are
-based on an architectural specification which is independent or any particular
-CPU model or implementation.  Older families such as the Motorola 68000 and the
-Intel x86 evolved as the manufacturer strived to produce higher performance
-processor models which maintained binary compatibility with older models.
-
-RTEMS takes advantage of the similarity of the various models within a CPU
-family.  Although the models do vary in significant ways, the high level of
-compatibility makes it possible to share the bulk of the CPU dependent
-executive code across the entire family.  Each processor family supported by
-RTEMS has a list of features which vary between CPU models within a family.
-For example, the most common model dependent feature regardless of CPU family
-is the presence or absence of a floating point unit or coprocessor.  When
-defining the list of features present on a particular CPU model, one simply
-notes that floating point hardware is or is not present and defines a single
-constant appropriately.  Conditional compilation is utilized to include the
-appropriate source code for this CPU model's feature set.  It is important to
-note that this means that RTEMS is thus compiled using the appropriate feature
-set and compilation flags optimal for this CPU model used.  The alternative
-would be to generate a binary which would execute on all family members using
-only the features which were always present.
-
-The set of CPU model feature macros are defined in the
-:file:`cpukit/score/cpu/CPU/rtems/score/cpu.h` based upon the GNU tools
-multilib variant that is appropriate for the particular CPU model defined on
-the compilation command line.
-
-In each of the architecture specific chapters, this section presents the set of
-features which vary across various implementations of the architecture that may
-be of importance to RTEMS application developers.
-
-The subsections will vary amongst the target architecture chapters as the
-specific features may vary.  However, each port will include a few common
-features such as the CPU Model Name and presence of a hardware Floating Point
-Unit.  The common features are described here.
-
-CPU Model Name
---------------
-
-The macro ``CPU_MODEL_NAME`` is a string which designates the name of this CPU
-model.  For example, for the MC68020 processor model from the m68k
-architecture, this macro is set to the string "mc68020".
-
-Floating Point Unit
--------------------
-
-In most architectures, the presence of a floating point unit is an option.  It
-does not matter whether the hardware floating point support is incorporated
-on-chip or is an external coprocessor as long as it appears an FPU per the ISA.
-However, if a hardware FPU is not present, it is possible that the floating
-point emulation library for this CPU is not reentrant and thus context switched
-by RTEMS.
-
-RTEMS provides two feature macros to indicate the FPU configuration:
-
-- CPU_HARDWARE_FP
-  is set to TRUE to indicate that a hardware FPU is present.
-
-- CPU_SOFTWARE_FP
-  is set to TRUE to indicate that a hardware FPU is not present and that the FP
-  software emulation will be context switched.
-
-Multilibs
-=========
-
-Newlib and GCC provide several target libraries like the :file:`libc.a`,
-:file:`libm.a` and :file:`libgcc.a`.  These libraries are artifacts of the GCC
-build process.  Newlib is built together with GCC.  To provide optimal support
-for various chip derivatives and instruction set revisions multiple variants of
-these libraries are available for each architecture.  For example one set may
-use software floating point support and another set may use hardware floating
-point instructions.  These sets of libraries are called *multilibs*.  Each
-library set corresponds to an application binary interface (ABI) and
-instruction set.
-
-A multilib variant can be usually detected via built-in compiler defines at
-compile-time.  This mechanism is used by RTEMS to select for example the
-context switch support for a particular BSP.  The built-in compiler defines
-corresponding to multilibs are the only architecture specific defines allowed
-in the ``cpukit`` area of the RTEMS sources.
-
-Invoking the GCC with the ``-print-multi-lib`` option lists the available
-multilibs.  Each line of the output describes one multilib variant.  The
-default variant is denoted by ``.`` which is selected when no or contradicting
-GCC machine options are selected.  The multilib selection for a target is
-specified by target makefile fragments (see file :file:`t-rtems` in the GCC
-sources and section *The Target Makefile Fragment*
-(https://gcc.gnu.org/onlinedocs/gccint/Target-Fragment.html#Target-Fragment)
-in the *GCC Internals Manual* (https://gcc.gnu.org/onlinedocs/gccint/).
-
-Calling Conventions
-===================
-
-Each high-level language compiler generates subroutine entry and exit code
-based upon a set of rules known as the compiler's calling convention.  These
-rules address the following issues:
-
-- register preservation and usage
-
-- parameter passing
-
-- call and return mechanism
-
-A compiler's calling convention is of importance when interfacing to
-subroutines written in another language either assembly or high-level.  Even
-when the high-level language and target processor are the same, different
-compilers may use different calling conventions.  As a result, calling
-conventions are both processor and compiler dependent.
-
-Calling Mechanism
------------------
-
-In each of the architecture specific chapters, this subsection will describe
-the instruction(s) used to perform a *normal* subroutine invocation.  All RTEMS
-directives are invoked as *normal* C language functions so it is important to
-the user application to understand the call and return mechanism.
-
-Register Usage
---------------
-
-In each of the architecture specific chapters, this subsection will detail the
-set of registers which are *NOT* preserved across subroutine invocations.  The
-registers which are not preserved are assumed to be available for use as
-scratch registers.  Therefore, the contents of these registers should not be
-assumed upon return from any RTEMS directive.
-
-In some architectures, there may be a set of registers made available
-automatically as a side-effect of the subroutine invocation mechanism.
-
-Parameter Passing
------------------
-
-In each of the architecture specific chapters, this subsection will describe
-the mechanism by which the parameters or arguments are passed by the caller to
-a subroutine.  In some architectures, all parameters are passed on the stack
-while in others some are passed in registers.
-
-User-Provided Routines
-----------------------
-
-All user-provided routines invoked by RTEMS, such as user extensions, device
-drivers, and MPCI routines, must also adhere to these calling conventions.
-
-Memory Model
-============
-
-A processor may support any combination of memory models ranging from pure
-physical addressing to complex demand paged virtual memory systems.  RTEMS
-supports a flat memory model which ranges contiguously over the processor's
-allowable address space.  RTEMS does not support segmentation or virtual memory
-of any kind.  The appropriate memory model for RTEMS provided by the targeted
-processor and related characteristics of that model are described in this
-chapter.
-
-Flat Memory Model
------------------
-
-Most RTEMS target processors can be initialized to support a flat address
-space.  Although the size of addresses varies between architectures, on most
-RTEMS targets, an address is 32-bits wide which defines addresses ranging from
-0x00000000 to 0xFFFFFFFF (4 gigabytes).  Each address is represented by a
-32-bit value and is byte addressable.  The address may be used to reference a
-single byte, word (2-bytes), or long word (4 bytes).  Memory accesses within
-this address space may be performed in little or big endian fashion.
-
-On smaller CPU architectures supported by RTEMS, the address space may only be
-20 or 24 bits wide.
-
-If the CPU model has support for virtual memory or segmentation, it is the
-responsibility of the Board Support Package (BSP) to initialize the MMU
-hardware to perform address translations which correspond to flat memory model.
-
-In each of the architecture specific chapters, this subsection will describe
-any architecture characteristics that differ from this general description.
-
-Interrupt Processing
-====================
-
-Different types of processors respond to the occurrence of an interrupt in its
-own unique fashion. In addition, each processor type provides a control
-mechanism to allow for the proper handling of an interrupt.  The processor
-dependent response to the interrupt modifies the current execution state and
-results in a change in the execution stream.  Most processors require that an
-interrupt handler utilize some special control mechanisms to return to the
-normal processing stream.  Although RTEMS hides many of the processor dependent
-details of interrupt processing, it is important to understand how the RTEMS
-interrupt manager is mapped onto the processor's unique architecture.
-
-RTEMS supports a dedicated interrupt stack for all architectures.  On
-architectures with hardware support for a dedicated interrupt stack, it will be
-initialized such that when an interrupt occurs, the processor automatically
-switches to this dedicated stack.  On architectures without hardware support
-for a dedicated interrupt stack which is separate from those of the tasks,
-RTEMS will support switching to a dedicated stack for interrupt processing.
-
-Without a dedicated interrupt stack, every task in the system MUST have enough
-stack space to accommodate the worst case stack usage of that particular task
-and the interrupt service routines COMBINED.  By supporting a dedicated
-interrupt stack, RTEMS significantly lowers the stack requirements for each
-task.
-
-A nested interrupt is processed similarly with the exception that since the CPU
-is already executing on the interrupt stack, there is no need to switch to the
-interrupt stack.
-
-In some configurations, RTEMS allocates the interrupt stack from the Workspace
-Area.  The amount of memory allocated for the interrupt stack is user
-configured and based upon the ``confdefs.h`` parameter
-``CONFIGURE_INTERRUPT_STACK_SIZE``.  This parameter is described in detail in
-the Configuring a System chapter of the User's Guide.  On configurations in
-which RTEMS allocates the interrupt stack, during the initialization process,
-RTEMS will also install its interrupt stack.  In other configurations, the
-interrupt stack is allocated and installed by the Board Support Package (BSP).
-
-In each of the architecture specific chapters, this section discesses the
-interrupt response and control mechanisms of the architecture as they pertain
-to RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-In each of the architecture specific chapters, this subsection will describe
-the architecture specific details of the interrupt vectoring process.  In
-particular, it should include a description of the Interrupt Stack Frame (ISF).
-
-Interrupt Levels
-----------------
-
-In each of the architecture specific chapters, this subsection will describe
-how the interrupt levels available on this particular architecture are mapped
-onto the 255 reserved in the task mode.  The interrupt level value of zero (0)
-should always mean that interrupts are enabled.
-
-Any use of an interrupt level that is is not undefined on a particular
-architecture may result in behavior that is unpredictable.
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-During the execution of directive calls, critical sections of code may be
-executed.  When these sections are encountered, RTEMS disables all external
-interrupts before the execution of this section and restores them to the
-previous level upon completion of the section.  RTEMS has been optimized to
-ensure that interrupts are disabled for the shortest number of instructions
-possible.  Since the precise number of instructions and their execution time
-varies based upon target CPU family, CPU model, board memory speed, compiler
-version, and optimization level, it is not practical to provide the precise
-number for all possible RTEMS configurations.
-
-Historically, the measurements were made by hand analyzing and counting the
-execution time of instruction sequences during interrupt disable critical
-sections.  For reference purposes, on a 16 Mhz Motorola MC68020, the maximum
-interrupt disable period was typically approximately ten (10) to thirteen (13)
-microseconds.  This architecture was memory bound and had a slow bit scan
-instruction.  In contrast, during the same period a 14 Mhz SPARC would have a
-worst case disable time of approximately two (2) to three (3) microseconds
-because it had a single cycle bit scan instruction and used fewer cycles for
-memory accesses.
-
-If you are interested in knowing the worst case execution time for a particular
-version of RTEMS, please contact OAR Corporation and we will be happy to
-product the results as a consulting service.
-
-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.
-
-Default Fatal Error Processing
-==============================
-
-Upon detection of a fatal error by either the application or RTEMS during
-initialization the ``rtems_fatal_error_occurred`` directive supplied by the
-Fatal Error Manager is invoked.  The Fatal Error Manager will invoke the
-user-supplied fatal error handlers.  If no user-supplied handlers are
-configured or all of them return without taking action to shutdown the
-processor or reset, a default fatal error handler is invoked.
-
-Most of the action performed as part of processing the fatal error are
-described in detail in the Fatal Error Manager chapter in the User's Guide.
-However, the if no user provided extension or BSP specific fatal error handler
-takes action, the final default action is to invoke a CPU architecture specific
-function.  Typically this function disables interrupts and halts the processor.
-
-In each of the architecture specific chapters, this describes the precise
-operations of the default CPU specific fatal error handler.
-
-Symmetric Multiprocessing
-=========================
-
-This section contains information about the Symmetric Multiprocessing (SMP)
-status of a particular architecture.
-
-Thread-Local Storage
-====================
-
-In order to support thread-local storage (TLS) the CPU port must implement the
-facilities mandated by the application binary interface (ABI) of the CPU
-architecture.  The CPU port must initialize the TLS area in the
-``_CPU_Context_Initialize()`` function.  There are support functions available
-via ``#include <rtems/score/tls.h>`` which implement Variants I and II
-according to Ulrich Drepper, *ELF Handling For Thread-Local Storage*.
-
-``_TLS_TCB_at_area_begin_initialize()``
-    Uses Variant I, TLS offsets emitted by linker takes the TCB into account.
-    For a reference implementation see :file:`cpukit/score/cpu/arm/cpu.c`.
-
-``_TLS_TCB_before_TLS_block_initialize()``
-    Uses Variant I, TLS offsets emitted by linker neglects the TCB.  For a
-    reference implementation see
-    :file:`c/src/lib/libcpu/powerpc/new-exceptions/cpu.c`.
-
-``_TLS_TCB_after_TLS_block_initialize()``
-    Uses Variant II.  For a reference implementation see
-    :file:`cpukit/score/cpu/sparc/cpu.c`.
-
-The board support package (BSP) must provide the following sections and symbols
-in its linker command file:
-
-.. code-block:: c
-
-    .tdata : {
-      _TLS_Data_begin = .;
-      *(.tdata .tdata.* .gnu.linkonce.td.*)
-      _TLS_Data_end = .;
-    }
-    .tbss : {
-      _TLS_BSS_begin = .;
-      *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon)
-      _TLS_BSS_end = .;
-    }
-    _TLS_Data_size = _TLS_Data_end - _TLS_Data_begin;
-    _TLS_Data_begin = _TLS_Data_size != 0 ? _TLS_Data_begin : _TLS_BSS_begin;
-    _TLS_Data_end = _TLS_Data_size != 0 ? _TLS_Data_end : _TLS_BSS_begin;
-    _TLS_BSS_size = _TLS_BSS_end - _TLS_BSS_begin;
-    _TLS_Size = _TLS_BSS_end - _TLS_Data_begin;
-    _TLS_Alignment = MAX (ALIGNOF (.tdata), ALIGNOF (.tbss));
-
-CPU counter
-===========
-
-The CPU support must implement the CPU counter interface.  A CPU counter is
-some free-running counter.  It ticks usually with a frequency close to the CPU
-or system bus clock.  On some architectures the actual implementation is board
-support package dependent.  The CPU counter is used for profiling of low-level
-functions.  It is also used to implement two busy wait functions
-``rtems_counter_delay_ticks()`` and ``rtems_counter_delay_nanoseconds()`` which
-may be used in device drivers.  It may be also used as an entropy source for
-random number generators.
-
-The CPU counter interface uses a CPU port specific unsigned integer type
-``CPU_Counter_ticks`` to represent CPU counter values.  The CPU port must
-provide the following two functions
-
-- ``_CPU_Counter_read()`` to read the current CPU counter value, and
-
-- ``_CPU_Counter_difference()`` to get the difference between two CPU
-  counter values.
-
-Interrupt Profiling
-===================
-
-The RTEMS profiling needs support by the CPU port for the interrupt entry and
-exit times.  In case profiling is enabled via the RTEMS build configuration
-option ``--enable-profiling`` (in this case the pre-processor symbol
-``RTEMS_PROFILING`` is defined) the CPU port may provide data for the interrupt
-entry and exit times of the outer-most interrupt.  The CPU port can feed
-interrupt entry and exit times with the
-``_Profiling_Outer_most_interrupt_entry_and_exit()`` function (``#include
-<rtems/score/profiling.h>``).  For an example please have a look at
-:file:`cpukit/score/cpu/arm/arm_exc_interrupt.S`.
-
-Board Support Packages
-======================
-
-An RTEMS Board Support Package (BSP) must be designed to support a particular
-processor model and target board combination.
-
-In each of the architecture specific chapters, this section will present a
-discussion of architecture specific BSP issues.  For more information on
-developing a BSP, refer to BSP and Device Driver Development Guide and the
-chapter titled Board Support Packages in the RTEMS Applications User's Guide.
-
-System Reset
-------------
-
-An RTEMS based application is initiated or re-initiated when the processor is
-reset or transfer is passed to it from a boot monitor or ROM monitor.
-
-In each of the architecture specific chapters, this subsection describes the
-actions that the BSP must tak assuming the application gets control when the
-microprocessor is reset.