@c
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@c
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@c COPYRIGHT (c) 1988-2002.
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@c COPYRIGHT (c) 1988-2002.
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@c On-Line Applications Research Corporation (OAR).
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@c On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c All rights reserved.
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@c
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@c
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@c cpumodels.t,v 1.6 2002/01/17 21:47:45 joel Exp
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@c cpumodels.t,v 1.6 2002/01/17 21:47:45 joel Exp
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@c
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@c
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@chapter CPU Model Variations
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@chapter CPU Model Variations
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XXX enhance using portability presentation from CS595 class. See
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XXX enhance using portability presentation from CS595 class. See
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general/portability.ppt.
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general/portability.ppt.
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Since the text in the next section was written, RTEMS view of
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Since the text in the next section was written, RTEMS view of
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portability has grown to distinguish totally portable, CPU
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portability has grown to distinguish totally portable, CPU
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family dependent, CPU model dependent, peripheral chip dependent
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family dependent, CPU model dependent, peripheral chip dependent
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and board dependent. This text was part of a larger paper that
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and board dependent. This text was part of a larger paper that
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did not even cover portability completely as it existed when this
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did not even cover portability completely as it existed when this
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was written and certainly is out of date now. :)
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was written and certainly is out of date now. :)
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@section Overview of RTEMS Portability
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@section Overview of RTEMS Portability
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RTEMS was designed to be a highly portable, reusable software component.
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RTEMS was designed to be a highly portable, reusable software component.
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This reflects the fundamental nature of embedded systems in which hardware
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This reflects the fundamental nature of embedded systems in which hardware
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components, ranging from boards to peripherals to even the processor
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components, ranging from boards to peripherals to even the processor
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itself, are selected specifically to meet the requirements of a particular
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itself, are selected specifically to meet the requirements of a particular
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project.
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project.
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@subsection Processor Families
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@subsection Processor Families
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Since there are a wide variety of embedded systems, there are a wide
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Since there are a wide variety of embedded systems, there are a wide
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variety of processors targeting embedded systems. RTEMS alleviates some of
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variety of processors targeting embedded systems. RTEMS alleviates some of
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the burden on the embedded systems programmer by providing a consistent,
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the burden on the embedded systems programmer by providing a consistent,
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high-performance environment regardless of the target processor. RTEMS
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high-performance environment regardless of the target processor. RTEMS
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has been ported to a variety of microprocessor families including:
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has been ported to a variety of microprocessor families including:
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@itemize @bullet
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@itemize @bullet
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@item Motorola ColdFire
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@item Motorola ColdFire
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@item Motorola MC68xxx
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@item Motorola MC68xxx
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@item Motorola MC683xx
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@item Motorola MC683xx
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@item Intel ix86 (i386 and above)
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@item Intel ix86 (i386 and above)
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@item Intel i960
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@item Intel i960
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@item MIPS
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@item MIPS
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@item PowerPC 4xx, 5xx, 6xx, 7xx, and 8xx
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@item PowerPC 4xx, 5xx, 6xx, 7xx, and 8xx
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@item SPARC
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@item SPARC
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@item Hewlett-Packard PA-RISC
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@item Hewlett-Packard PA-RISC
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@item AMD A29K
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@item AMD A29K
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@end itemize
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@end itemize
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In addition, there is a port of RTEMS to UNIX that uses standard UNIX
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In addition, there is a port of RTEMS to UNIX that uses standard UNIX
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services to simulate the embedded environment.
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services to simulate the embedded environment.
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Each RTEMS port supplies a well-defined set of services that are the
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Each RTEMS port supplies a well-defined set of services that are the
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foundation for the highly portable RTEMS and POSIX API implementations.
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foundation for the highly portable RTEMS and POSIX API implementations.
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When porting to a new processor family, one must provide the processor
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When porting to a new processor family, one must provide the processor
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dependent implementation of these services. This set of processor
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dependent implementation of these services. This set of processor
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dependent core services includes software to perform interrupt
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dependent core services includes software to perform interrupt
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dispatching, context switches, and manipulate task register sets.
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dispatching, context switches, and manipulate task register sets.
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The RTEMS approach to handling varying processor models reflects the
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The RTEMS approach to handling varying processor models reflects the
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approach taken by the designers of the processors themselves. In each
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approach taken by the designers of the processors themselves. In each
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processor family, there is a core architecture that must be implemented on
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processor family, there is a core architecture that must be implemented on
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all processor models within the family to provide any level of
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all processor models within the family to provide any level of
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compatibility. Many of the modern RISC architectures refer to this as the
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compatibility. Many of the modern RISC architectures refer to this as the
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Architectural Definition. The Architectural Definition is intended to be
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Architectural Definition. The Architectural Definition is intended to be
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independent of any particular implementation. Additionally, there is a
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independent of any particular implementation. Additionally, there is a
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feature set which is allowed to vary in a defined way amongst the
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feature set which is allowed to vary in a defined way amongst the
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processor models. These feature sets may be defined as Optional in the
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processor models. These feature sets may be defined as Optional in the
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Architectural Definition, be left as implementation defined
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Architectural Definition, be left as implementation defined
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characteristics, or be processor model specific extensions. Support for
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characteristics, or be processor model specific extensions. Support for
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floating point, virtual memory, and low power mode are common Optional
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floating point, virtual memory, and low power mode are common Optional
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features included in an Architectural Definition.
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features included in an Architectural Definition.
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The processor family dependent software in RTEMS includes a definition of
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The processor family dependent software in RTEMS includes a definition of
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which features are present in each supported processor model. This often
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which features are present in each supported processor model. This often
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makes adding support for a new processor model within a supported family
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makes adding support for a new processor model within a supported family
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as simple as determining which features are present in the new processor
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as simple as determining which features are present in the new processor
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implementation. If the new processor model varies in a way previously
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implementation. If the new processor model varies in a way previously
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unaccounted for, then this must be addressed. This could be the result of
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unaccounted for, then this must be addressed. This could be the result of
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a new Optional feature set being added to the Architectural Definition.
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a new Optional feature set being added to the Architectural Definition.
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Alternatively, this particular processor model could have a new and
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Alternatively, this particular processor model could have a new and
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different implementation of a feature left as undefined in the
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different implementation of a feature left as undefined in the
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Architectural Definition. This would require software to be written to
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Architectural Definition. This would require software to be written to
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utilize that feature.
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utilize that feature.
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There is a relatively small set of features that may vary in a processor
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There is a relatively small set of features that may vary in a processor
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family. As the number of processor models in the family grow, the
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family. As the number of processor models in the family grow, the
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addition of each new model only requires adding an entry for the new model
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addition of each new model only requires adding an entry for the new model
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to the single feature table. It does not require searching for every
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to the single feature table. It does not require searching for every
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conditional based on processor model and adding the new model in the
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conditional based on processor model and adding the new model in the
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appropriate place. This significantly eases the burden of adding a new
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appropriate place. This significantly eases the burden of adding a new
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processor model as it centralizes and logically simplifies the process.
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processor model as it centralizes and logically simplifies the process.
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@subsection Boards
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@subsection Boards
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Being portable both between models within a processor family and across
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Being portable both between models within a processor family and across
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processor families is not enough to address the needs of embedded systems
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processor families is not enough to address the needs of embedded systems
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developers. Custom board development is the norm for embedded systems.
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developers. Custom board development is the norm for embedded systems.
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Each of these boards is optimized for a particular project. The processor
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Each of these boards is optimized for a particular project. The processor
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and peripheral set have been chosen to meet a particular set of system
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and peripheral set have been chosen to meet a particular set of system
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requirements. The tools in the embedded systems developers’ toolbox must
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requirements. The tools in the embedded systems developers’ toolbox must
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support their project’s unique board. RTEMS addresses this issue via the
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support their project’s unique board. RTEMS addresses this issue via the
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Board Support Package.
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Board Support Package.
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RTEMS segregates board specific code to make it possible for the embedded
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RTEMS segregates board specific code to make it possible for the embedded
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systems developer to easily replace and customize this software. A
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systems developer to easily replace and customize this software. A
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minimal Board Support Package includes device drivers for a clock tick,
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minimal Board Support Package includes device drivers for a clock tick,
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console I/O, and a benchmark timer (optional) as well as startup and
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console I/O, and a benchmark timer (optional) as well as startup and
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miscellaneous support code. The Board Support Package for a project may
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miscellaneous support code. The Board Support Package for a project may
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be extended to include the device drivers for any peripherals on the
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be extended to include the device drivers for any peripherals on the
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custom board.
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custom board.
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@subsection Applications
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@subsection Applications
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One important design goal of RTEMS was to provide a bridge between the
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One important design goal of RTEMS was to provide a bridge between the
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application software and the target hardware. Most hardware dependencies
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application software and the target hardware. Most hardware dependencies
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for real-time applications can be localized to the low level device
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for real-time applications can be localized to the low level device
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drivers which provide an abstracted view of the hardware. The RTEMS I/O
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drivers which provide an abstracted view of the hardware. The RTEMS I/O
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interface manager provides an efficient tool for incorporating these
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interface manager provides an efficient tool for incorporating these
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hardware dependencies into the system while simultaneously providing a
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hardware dependencies into the system while simultaneously providing a
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general mechanism to the application code that accesses them. A well
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general mechanism to the application code that accesses them. A well
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designed real-time system can benefit from this architecture by building a
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designed real-time system can benefit from this architecture by building a
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rich library of standard application components which can be used
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rich library of standard application components which can be used
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repeatedly in other real-time projects. The following figure illustrates
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repeatedly in other real-time projects. The following figure illustrates
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how RTEMS serves as a buffer between the project dependent application
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how RTEMS serves as a buffer between the project dependent application
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code and the target hardware.
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code and the target hardware.
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@section Coding Issues
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@section Coding Issues
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XXX deal with this as it applies to score/cpu. Section name may
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XXX deal with this as it applies to score/cpu. Section name may
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be bad.
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be bad.
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