[rtems-docs commit] cpu-supplement/powerpc: Rewrite
sebh at rtems.org
Wed Aug 23 07:26:14 UTC 2017
Author: Sebastian Huber <sebastian.huber at embedded-brains.de>
Date: Wed Aug 23 09:23:23 2017 +0200
Remove obsolete and duplicated information. Reference the ABI
specifications. Add 64-bit caveats.
cpu-supplement/powerpc.rst | 513 ++++-----------------------------------------
1 file changed, 38 insertions(+), 475 deletions(-)
diff --git a/cpu-supplement/powerpc.rst b/cpu-supplement/powerpc.rst
index cd7847b..c9b4539 100644
@@ -7,166 +7,6 @@
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
-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.
-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.
-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.
-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.
-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
-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.
-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
- indicates that the single-step trace enable (SE) and branch trace enable
- (BE) bits in the MSR are supported by this CPU model.
- indicates that only the single-step trace enable (SE) bit in the MSR is
- supported by this CPU model.
- 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.
- indicates that this CPU model has no low power mode support.
- indicates that this CPU model follows the low power model defined for the
@@ -212,66 +52,30 @@ The following multilibs are available:
#. ``me6500/m32/nof/noaltivec``: 32-bit instruction set for e6500 core
with software floating point support and no AltiVec
-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 at goth.sis.mot.com.
-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:
+#. ``me6500/m64``: 64-bit instruction set for e6500 core with FPU and
-| 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) |
+#. ``me6500/m64/nof/noaltivec``: 64-bit instruction set for e6500 core
+ with software floating point support and no AltiVec
-Floating Point Registers
+Application Binary Interface
-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.
+In 32-bit PowerPC configurations the ABI defined by
+`Power Architecture 32-bit Application Binary Interface Supplement 1.0 - Embedded <https://ftp.rtems.org/pub/rtems/people/sebh/Power-Arch-32-bit-ABI-supp-1.0-Embedded.pdf>`_
-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.
+In 64-bit PowerPC configurations the ABI defined by
+`Power Architecture 64-Bit ELF V2 ABI Specification, Version 1.1 <https://ftp.rtems.org/pub/rtems/people/sebh/ABI64BitOpenPOWERv1.1_16July2015_pub.pdf>`_
-The PowerPC architecture includes a number of special registers which are
-critical to the programming model:
+The following special-purpose registers are used by RTEMS:
*Special-Purpose Register General 0 (SPRG0)*
- On SMP configurations, this register contains the address of the per-CPU
+ In SMP configurations, this register contains the address of the per-CPU
control of the processor.
*Special-Purpose Register General 1 (SPRG1)*
@@ -281,247 +85,31 @@ critical to the programming model:
*Special-Purpose Register General 2 (SPRG2)*
This register contains the address of interrupt stack area begin.
-*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.
- 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.
- 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``)
-All RTEMS directives are invoked using the regular PowerPC EABI calling
-convention via the ``bl`` or``bla`` instructions.
-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.
-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-block:: c
- load third argument into r5
- load second argument into r4
- load first argument into r3
- invoke directive
-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
-Data Type Alignment Requirement
-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.
+The memory model is flat.
-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 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
-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
-- 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
-- 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.
-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:
- Setting bit 0 (the least significant bit) of the interrupt level enables
- the Critical Interrupt source, if it is available on this CPU model.
- Setting bit 1 of the interrupt level enables Machine Check execptions.
+There are exactly two interrupt levels on PowerPC with respect to RTEMS. Level
+zero corresponds to interrupts enabled. Level one corresponds to interrupts
- Setting bit 2 of the interrupt level enables External Interrupt execptions.
-All other bits in the RTEMS task interrupt level are ignored.
+The interrupt stack size can be configured via the
+``CONFIGURE_INTERRUPT_STACK_SIZE`` application configuration option.
Default Fatal Error Processing
-The default fatal error handler for this architecture performs the following
-- 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.
+The default fatal error handler is BSP-specific.
@@ -534,47 +122,22 @@ Thread-Local Storage
Thread-local storage is supported.
-Board Support Packages
-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.
-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
-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.
+* The thread pointer is `r13` in contrast to `r2` used in the 32-bit ABI.
-- 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.
+* The TOC pointer is `r2`. It must be initialized as part of the C run-time
+ setup. A valid stack pointer is not enough to call C functions. They may
+ use the TOC to get addresses and constants.
-- Must disable all external interrupts (i.e. clear the EI (EE) bit of the
- machine state register).
+* The TOC must be within the first 4GiB of the address space. This simplifies
+ the interrupt prologue.
-- Must enable traps so window overflow and underflow conditions can be properly
+* The `PPC_REG_LOAD`, `PPC_REG_STORE`, `PPC_REG_STORE_UPDATE`, and
+ `PPC_REG_CMP` macros are available for assembly code to provide register size
+ operations selected by the GCC `m32` and `m64` options.
-- Must initialize the PowerPC's initial Exception Table with default handlers.
+* The `MSR[CM]` bit must be set all the time, otherwise the MMU translation my
+ yield unexpected results. The `EPCR[ICM]` or `EPCR[GICM]` bits may be used
+ to enable the 64-bit compute mode for exceptions.
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