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authorAmar Takhar <amar@rtems.org>2016-01-16 20:13:02 -0500
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+PowerPC Specific Information
+############################
+
+This chapter discusses the PowerPC architecture dependencies
+in this port of RTEMS. The PowerPC family has a wide variety
+of implementations by a range of vendors. Consequently,
+there are many, many CPU models within it.
+
+It is highly recommended that the PowerPC RTEMS
+application developer obtain and become familiar with the
+documentation for the processor being used as well as the
+specification for the revision of the PowerPC architecture which
+corresponds to that processor.
+
+**PowerPC Architecture Documents**
+
+For information on the PowerPC architecture, refer to
+the following documents available from Motorola and IBM:
+
+- *PowerPC Microprocessor Family: The Programming Environment*
+ (Motorola Document MPRPPCFPE-01).
+
+- *IBM PPC403GB Embedded Controller User’s Manual*.
+
+- *PoweRisControl MPC500 Family RCPU RISC Central Processing
+ Unit Reference Manual* (Motorola Document RCPUURM/AD).
+
+- *PowerPC 601 RISC Microprocessor User’s Manual*
+ (Motorola Document MPR601UM/AD).
+
+- *PowerPC 603 RISC Microprocessor User’s Manual*
+ (Motorola Document MPR603UM/AD).
+
+- *PowerPC 603e RISC Microprocessor User’s Manual*
+ (Motorola Document MPR603EUM/AD).
+
+- *PowerPC 604 RISC Microprocessor User’s Manual*
+ (Motorola Document MPR604UM/AD).
+
+- *PowerPC MPC821 Portable Systems Microprocessor User’s Manual*
+ (Motorola Document MPC821UM/AD).
+
+- *PowerQUICC MPC860 User’s Manual* (Motorola Document MPC860UM/AD).
+
+Motorola maintains an on-line electronic library for the PowerPC
+at the following URL:
+
+- http://www.mot.com/powerpc/library/library.html
+
+This site has a a wealth of information and examples. Many of the
+manuals are available from that site in electronic format.
+
+**PowerPC Processor Simulator Information**
+
+PSIM is a program which emulates the Instruction Set Architecture
+of the PowerPC microprocessor family. It is reely available in source
+code form under the terms of the GNU General Public License (version
+2 or later). PSIM can be integrated with the GNU Debugger (gdb) to
+execute and debug PowerPC executables on non-PowerPC hosts. PSIM
+supports the addition of user provided device models which can be
+used to allow one to develop and debug embedded applications using
+the simulator.
+
+The latest version of PSIM is included in GDB and enabled on pre-built
+binaries provided by the RTEMS Project.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across PowerPC implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/powerpc/powerpc.h`` based upon the particular CPU
+model specified on the compilation command line.
+
+Alignment
+---------
+
+The macro PPC_ALIGNMENT is set to the PowerPC model’s worst case alignment
+requirement for data types on a byte boundary. This value is used
+to derive the alignment restrictions for memory allocated from
+regions and partitions.
+
+Cache Alignment
+---------------
+
+The macro PPC_CACHE_ALIGNMENT is set to the line size of the cache. It is
+used to align the entry point of critical routines so that as much code
+as possible can be retrieved with the initial read into cache. This
+is done for the interrupt handler as well as the context switch routines.
+
+In addition, the "shortcut" data structure used by the PowerPC implementation
+to ease access to data elements frequently accessed by RTEMS routines
+implemented in assembly language is aligned using this value.
+
+Maximum Interrupts
+------------------
+
+The macro PPC_INTERRUPT_MAX is set to the number of exception sources
+supported by this PowerPC model.
+
+Has Double Precision Floating Point
+-----------------------------------
+
+The macro PPC_HAS_DOUBLE is set to 1 to indicate that the PowerPC model
+has support for double precision floating point numbers. This is
+important because the floating point registers need only be four bytes
+wide (not eight) if double precision is not supported.
+
+Critical Interrupts
+-------------------
+
+The macro PPC_HAS_RFCI is set to 1 to indicate that the PowerPC model
+has the Critical Interrupt capability as defined by the IBM 403 models.
+
+Use Multiword Load/Store Instructions
+-------------------------------------
+
+The macro PPC_USE_MULTIPLE is set to 1 to indicate that multiword load and
+store instructions should be used to perform context switch operations.
+The relative efficiency of multiword load and store instructions versus
+an equivalent set of single word load and store instructions varies based
+upon the PowerPC model.
+
+Instruction Cache Size
+----------------------
+
+The macro PPC_I_CACHE is set to the size in bytes of the instruction cache.
+
+Data Cache Size
+---------------
+
+The macro PPC_D_CACHE is set to the size in bytes of the data cache.
+
+Debug Model
+-----------
+
+The macro PPC_DEBUG_MODEL is set to indicate the debug support features
+present in this CPU model. The following debug support feature sets
+are currently supported:
+
+*``PPC_DEBUG_MODEL_STANDARD``*
+ indicates that the single-step trace enable (SE) and branch trace
+ enable (BE) bits in the MSR are supported by this CPU model.
+
+*``PPC_DEBUG_MODEL_SINGLE_STEP_ONLY``*
+ indicates that only the single-step trace enable (SE) bit in the MSR
+ is supported by this CPU model.
+
+*``PPC_DEBUG_MODEL_IBM4xx``*
+ indicates that the debug exception enable (DE) bit in the MSR is supported
+ by this CPU model. At this time, this particular debug feature set
+ has only been seen in the IBM 4xx series.
+
+Low Power Model
+~~~~~~~~~~~~~~~
+
+The macro PPC_LOW_POWER_MODE is set to indicate the low power model
+supported by this CPU model. The following low power modes are currently
+supported.
+
+*``PPC_LOW_POWER_MODE_NONE``*
+ indicates that this CPU model has no low power mode support.
+
+*``PPC_LOW_POWER_MODE_STANDARD``*
+ indicates that this CPU model follows the low power model defined for
+ the PPC603e.
+
+Multilibs
+=========
+
+The following multilibs are available:
+
+# ``.``: 32-bit PowerPC with FPU
+
+# ``nof``: 32-bit PowerPC with software floating point support
+
+# ``m403``: Instruction set for PPC403 with FPU
+
+# ``m505``: Instruction set for MPC505 with FPU
+
+# ``m603e``: Instruction set for MPC603e with FPU
+
+# ``m603e/nof``: Instruction set for MPC603e with software floating
+ point support
+
+# ``m604``: Instruction set for MPC604 with FPU
+
+# ``m604/nof``: Instruction set for MPC604 with software floating point
+ support
+
+# ``m860``: Instruction set for MPC860 with FPU
+
+# ``m7400``: Instruction set for MPC7500 with FPU
+
+# ``m7400/nof``: Instruction set for MPC7500 with software floating
+ point support
+
+# ``m8540``: Instruction set for e200, e500 and e500v2 cores with
+ single-precision FPU and SPE
+
+# ``m8540/gprsdouble``: Instruction set for e200, e500 and e500v2 cores
+ with double-precision FPU and SPE
+
+# ``m8540/nof/nospe``: Instruction set for e200, e500 and e500v2 cores
+ with software floating point support and no SPE
+
+# ``me6500/m32``: 32-bit instruction set for e6500 core with FPU and
+ AltiVec
+
+# ``me6500/m32/nof/noaltivec``: 32-bit instruction set for e6500 core
+ with software floating point support and no AltiVec
+
+Calling Conventions
+===================
+
+RTEMS supports the Embedded Application Binary Interface (EABI)
+calling convention. Documentation for EABI is available by sending
+a message with a subject line of "EABI" to eabi@goth.sis.mot.com.
+
+Programming Model
+-----------------
+
+This section discusses the programming model for the
+PowerPC architecture.
+
+Non-Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture defines thirty-two non-floating point registers
+directly visible to the programmer. In thirty-two bit implementations, each
+register is thirty-two bits wide. In sixty-four bit implementations, each
+register is sixty-four bits wide.
+
+These registers are referred to as ``gpr0`` to ``gpr31``.
+
+Some of the registers serve defined roles in the EABI programming model.
+The following table describes the role of each of these registers:
+.. code:: c
+
+ +---------------+----------------+------------------------------+
+ | Register Name | Alternate Name | Description |
+ +---------------+----------------+------------------------------+
+ | r1 | sp | stack pointer |
+ +---------------+----------------+------------------------------+
+ | | | global pointer to the Small |
+ | r2 | na | Constant Area (SDA2) |
+ +---------------+----------------+------------------------------+
+ | r3 - r12 | na | parameter and result passing |
+ +---------------+----------------+------------------------------+
+ | | | global pointer to the Small |
+ | r13 | na | Data Area (SDA) |
+ +---------------+----------------+------------------------------+
+
+Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture includes thirty-two, sixty-four bit
+floating point registers. All PowerPC floating point instructions
+interpret these registers as 32 double precision floating point registers,
+regardless of whether the processor has 64-bit or 32-bit implementation.
+
+The floating point status and control register (fpscr) records exceptions
+and the type of result generated by floating-point operations.
+Additionally, it controls the rounding mode of operations and allows the
+reporting of floating exceptions to be enabled or disabled.
+
+Special Registers
+~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture includes a number of special registers
+which are critical to the programming model:
+
+*Machine State Register*
+ The MSR contains the processor mode, power management mode, endian mode,
+ exception information, privilege level, floating point available and
+ floating point excepiton mode, address translation information and
+ the exception prefix.
+
+*Link Register*
+ The LR contains the return address after a function call. This register
+ must be saved before a subsequent subroutine call can be made. The
+ use of this register is discussed further in the *Call and Return
+ Mechanism* section below.
+
+*Count Register*
+ The CTR contains the iteration variable for some loops. It may also be used
+ for indirect function calls and jumps.
+
+Call and Return Mechanism
+-------------------------
+
+The PowerPC architecture supports a simple yet effective call
+and return mechanism. A subroutine is invoked
+via the "branch and link" (``bl``) and
+"brank and link absolute" (``bla``)
+instructions. This instructions place the return address
+in the Link Register (LR). The callee returns to the caller by
+executing a "branch unconditional to the link register" (``blr``)
+instruction. Thus the callee returns to the caller via a jump
+to the return address which is stored in the LR.
+
+The previous contents of the LR are not automatically saved
+by either the ``bl`` or ``bla``. It is the responsibility
+of the callee to save the contents of the LR before invoking
+another subroutine. If the callee invokes another subroutine,
+it must restore the LR before executing the ``blr`` instruction
+to return to the caller.
+
+It is important to note that the PowerPC subroutine
+call and return mechanism does not automatically save and
+restore any registers.
+
+The LR may be accessed as special purpose register 8 (``SPR8``) using the
+"move from special register" (``mfspr``) and
+"move to special register" (``mtspr``) instructions.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using the regular
+PowerPC EABI calling convention via the ``bl`` or``bla`` instructions.
+
+Register Usage
+--------------
+
+As discussed above, the call instruction does not
+automatically save any registers. It is the responsibility
+of the callee to save and restore any registers which must be preserved
+across subroutine calls. The callee is responsible for saving
+callee-preserved registers to the program stack and restoring them
+before returning to the caller.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed in the
+general purpose registers with the first argument in
+register 3 (``r3``), the second argument in general purpose
+register 4 (``r4``), and so forth until the seventh
+argument is in general purpose register 10 (``r10``).
+If there are more than seven arguments, then subsequent arguments
+are placed on the program stack. The following pseudo-code
+illustrates the typical sequence used to call a RTEMS directive
+with three (3) arguments:
+.. code:: c
+
+ load third argument into r5
+ load second argument into r4
+ load first argument into r3
+ invoke directive
+
+Memory Model
+============
+
+Flat Memory Model
+-----------------
+
+The PowerPC architecture supports a variety of memory models.
+RTEMS supports the PowerPC using a flat memory model with
+paging disabled. In this mode, the PowerPC automatically
+converts every address from a logical to a physical address
+each time it is used. The PowerPC uses information provided
+in the Block Address Translation (BAT) to convert these addresses.
+
+Implementations of the PowerPC architecture may be thirty-two or sixty-four bit.
+The PowerPC architecture supports a flat thirty-two or sixty-four bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes) in thirty-two bit implementations or to 0xFFFFFFFFFFFFFFFF
+in sixty-four bit implementations. Each address is represented
+by either a thirty-two bit or sixty-four bit value and is byte addressable.
+The address may be used to reference a single byte, half-word
+(2-bytes), word (4 bytes), or in sixty-four bit implementations a
+doubleword (8 bytes). Memory accesses within the address space are
+performed in big or little endian fashion by the PowerPC based
+upon the current setting of the Little-endian mode enable bit (LE)
+in the Machine State Register (MSR). While the processor is in
+big endian mode, memory accesses which are not properly aligned
+generate an "alignment exception" (vector offset 0x00600). In
+little endian mode, the PowerPC architecture does not require
+the processor to generate alignment exceptions.
+
+The following table lists the alignment requirements for a variety
+of data accesses:
+
+.. code:: c
+
+ +--------------+-----------------------+
+ | Data Type | Alignment Requirement |
+ +--------------+-----------------------+
+ | byte | 1 |
+ | half-word | 2 |
+ | word | 4 |
+ | doubleword | 8 |
+ +--------------+-----------------------+
+
+Doubleword load and store operations are only available in
+PowerPC CPU models which are sixty-four bit implementations.
+
+RTEMS does not directly support any PowerPC Memory Management
+Units, therefore, virtual memory or segmentation systems
+involving the PowerPC are not supported.
+
+.. COMMENT: COPYRIGHT (c) 1989-2007.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Interrupt Processing
+====================
+
+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. Discussed in this chapter are the PowerPC’s
+interrupt response and control mechanisms as they pertain to
+RTEMS.
+
+RTEMS and associated documentation uses the terms interrupt and vector.
+In the PowerPC architecture, these terms correspond to exception and
+exception handler, respectively. The terms will be used interchangeably
+in this manual.
+
+Synchronous Versus Asynchronous Exceptions
+------------------------------------------
+
+In the PowerPC architecture exceptions can be either precise or
+imprecise and either synchronous or asynchronous. Asynchronous
+exceptions occur when an external event interrupts the processor.
+Synchronous exceptions are caused by the actions of an
+instruction. During an exception SRR0 is used to calculate where
+instruction processing should resume. All instructions prior to
+the resume instruction will have completed execution. SRR1 is used to
+store the machine status.
+
+There are two asynchronous nonmaskable, highest-priority exceptions
+system reset and machine check. There are two asynchrononous maskable
+low-priority exceptions external interrupt and decrementer. Nonmaskable
+execptions are never delayed, therefore if two nonmaskable, asynchronous
+exceptions occur in immediate succession, the state information saved by
+the first exception may be overwritten when the subsequent exception occurs.
+
+The PowerPC arcitecure defines one imprecise exception, the imprecise
+floating point enabled exception. All other synchronous exceptions are
+precise. The synchronization occuring during asynchronous precise
+exceptions conforms to the requirements for context synchronization.
+
+Vectoring of Interrupt Handler
+------------------------------
+
+Upon determining that an exception can be taken the PowerPC automatically
+performs the following actions:
+
+- an instruction address is loaded into SRR0
+
+- bits 33-36 and 42-47 of SRR1 are loaded with information
+ specific to the exception.
+
+- bits 0-32, 37-41, and 48-63 of SRR1 are loaded with corresponding
+ bits from the MSR.
+
+- the MSR is set based upon the exception type.
+
+- instruction fetch and execution resumes, using the new MSR value, at a location specific to the execption type.
+
+If the interrupt handler was installed as an RTEMS
+interrupt handler, then upon receipt of the interrupt, the
+processor passes control to the RTEMS interrupt handler which
+performs the following actions:
+
+- saves the state of the interrupted task on it’s stack,
+
+- saves all registers which are not normally preserved
+ by the calling sequence so the user’s interrupt service
+ routine can be written in a high-level language.
+
+- if this is the outermost (i.e. non-nested) interrupt,
+ then the RTEMS interrupt handler switches from the current stack
+ to the interrupt stack,
+
+- enables exceptions,
+
+- invokes the vectors to a user interrupt service routine (ISR).
+
+Asynchronous interrupts are ignored while exceptions are
+disabled. Synchronous interrupts which occur while are
+disabled result in the CPU being forced into an error mode.
+
+A nested interrupt is processed similarly with the
+exception that the current stack need not be switched to the
+interrupt stack.
+
+Interrupt Levels
+----------------
+
+The PowerPC architecture supports only a single external
+asynchronous interrupt source. This interrupt source
+may be enabled and disabled via the External Interrupt Enable (EE)
+bit in the Machine State Register (MSR). Thus only two level (enabled
+and disabled) of external device interrupt priorities are
+directly supported by the PowerPC architecture.
+
+Some PowerPC implementations include a Critical Interrupt capability
+which is often used to receive interrupts from high priority external
+devices.
+
+The RTEMS interrupt level mapping scheme for the PowerPC is not
+a numeric level as on most RTEMS ports. It is a bit mapping in
+which the least three significiant bits of the interrupt level
+are mapped directly to the enabling of specific interrupt
+sources as follows:
+
+*Critical Interrupt*
+ Setting bit 0 (the least significant bit) of the interrupt level
+ enables the Critical Interrupt source, if it is available on this
+ CPU model.
+
+*Machine Check*
+ Setting bit 1 of the interrupt level enables Machine Check execptions.
+
+*External Interrupt*
+ Setting bit 2 of the interrupt level enables External Interrupt execptions.
+
+All other bits in the RTEMS task interrupt level are ignored.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture performs the
+following actions:
+
+- places the error code in r3, and
+
+- executes a trap instruction which results in a Program Exception.
+
+If the Program Exception returns, then the following actions are performed:
+
+- disables all processor exceptions by loading a 0 into the MSR, and
+
+- goes into an infinite loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is supported. Available platforms are the Freescale QorIQ P series (e.g.
+P1020) and T series (e.g. T2080, T4240).
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated or
+re-initiated when the PowerPC processor is reset. The PowerPC
+architecture defines a Reset Exception, but leaves the
+details of the CPU state as implementation specific. Please
+refer to the User’s Manual for the CPU model in question.
+
+In general, at power-up the PowerPC begin execution at address
+0xFFF00100 in supervisor mode with all exceptions disabled. For
+soft resets, the CPU will vector to either 0xFFF00100 or 0x00000100
+depending upon the setting of the Exception Prefix bit in the MSR.
+If during a soft reset, a Machine Check Exception occurs, then the
+CPU may execute a hard reset.
+
+Processor Initialization
+------------------------
+
+If this PowerPC implementation supports on-chip caching
+and this is to be utilized, then it should be enabled during the
+reset application initialization code. On-chip caching has been
+observed to prevent some emulators from working properly, so it
+may be necessary to run with caching disabled to use these emulators.
+
+In addition to the requirements described in the*Board Support Packages* chapter of the RTEMS C
+Applications User’s Manual for the reset code
+which is executed before the call to ``rtems_initialize_executive``,
+the PowrePC version has the following specific requirements:
+
+- Must leave the PR bit of the Machine State Register (MSR) set
+ to 0 so the PowerPC remains in the supervisor state.
+
+- Must set stack pointer (sp or r1) such that a minimum stack
+ size of MINIMUM_STACK_SIZE bytes is provided for the RTEMS initialization
+ sequence.
+
+- Must disable all external interrupts (i.e. clear the EI (EE)
+ bit of the machine state register).
+
+- Must enable traps so window overflow and underflow
+ conditions can be properly handled.
+
+- Must initialize the PowerPC’s initial Exception Table with default
+ handlers.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+