Document Sample

    Term Paper Presentation
         Umut Yazkurt

         CMPE 511
       Fall 2003-2004
   PowerPC is a RISC architecture.

    It was jointly designed by Apple, IBM, and Motorola by
    early 1990s.

    Aim was to form the basis of a new generation of
    high-performance low-cost products ranging from low
    cost embedded controllers to massively parallel

   Because of its already largely installed software base,
    they began with IBM’s POWER architecture which was
    developed for RS/6000 systems.
    Apple, IBM, and Motorola designed the first four members of the
    PowerPC microprocessor family simultaneously.

   PowerPC 601™ : the first 32 bit implementation of the PowerPC
    architecture providing medium levels of performance for desktop
    computers and workstations.

   PowerPC 603™ : a 32-bit low-power processor primarily for cost-
    sensitive desktop and portable personal computer systems.

   PowerPC 604™ : 32-bit implementations of the PowerPC
    architecture designed for use in high performance desktop,
    workstation, and symmetric multiprocessing computer systems.

   PowerPC 620™ : 64-bit implementation of the PowerPC architecture
    providing high levels of performance for technical and scientific
    workstations, application and LAN servers and symmetric
    multiprocessing computer systems.

                  601    604/604E    740/750            G4      G5
                  (G1)     (G2)        (G3)
First         1993       1994       1997         1999        2003
Clock Speed   50-120     166-350    200-366      500-1400      Up to
(MHZ)                                                          2000
L1 Cache      -          32kb inst 32kb inst     32kb inst   64kb inst
                         32kb data 32kb data     32kb data   32kb data
L2 Cache      -          -          256k – 1Mb   256kb-1Mb   512kb on
Support                                                      die
# of trans    2.8        3.6-5.1    6.35         10.5        Over 58
    The PowerPC architecture specifies an
    instruction set architecture (ISA).

   It is independent of implementation aspects.

    It allows anyone to design and fabricate
    compatible PowerPC processors independent of
    implementation differences as the technology
   All PowerPC processors run the same core
    PowerPC instruction set.

   They differ primarily in the degree of dedicated
    hardware support for multiple execution units,
    cache size and capability, length of pipeline, and
    interface busses.

   These differences result in different tradeoffs in
    processing performance, die area, and power
                Programming Model
   The PowerPC architecture is a full 64-bit architecture
    with full 64-bit integers and 64-bit logical address

   It also has a well defined 32-bit subset. Designers may
    implement either 32- or 64-bit machines. To enable 32-
    bit applications to run on all PowerPC processors, 64 bit
    machines are required to support a 32-bit operating

   The 32-bit processors have 32-bit wide general registers
    and branch-address registers; 64 bit processors have 64-
    bit wide registers.
                Programming Model
   Instructions always operate on machine’s full register
    width: 32 or 64 bits.

   Instructions are mode independent ; a given instruction
    operates the same on 32-bit machines , 64-bit machines,
    and 64-bit machines operating in 32-bit mode.

   A 64-bit machine operating in 32-bit mode passes only
    the low-order 32 bits of an address to the address
    translation mechanism, and the ALU calculates carry and
    over-flow based on a 32-bit result.
          Logical Address Space
   For 32-bit machines and 64-bit machines
    operating in the 32-bit mode, the linear
    array of bytes that can be addressed by a
    pointer is 4 gigabytes.

   For 64-bit machines operating in 64-bit
    mode, 18 terabytes of memory can be
   When the processor is first initialized, it is in supervisor
    (also called privileged) mode. In this mode, all processor
    resources, including registers and instructions are

   The processor can limit access to certain privileged
    registers and instructions by placing itself in user mode.

   This protection limits application code from being able to
    modify global and sensitive resources, such as the
    caches, memory management system, and timers.

Architecture defines five types of registers :

      Special Purpose Registers (SPRs)
      General Purpose Registers (GPRs)
      Floating Point Registers (FPRs)
      Device Control Registers (DCRs)
      Machine State Register (MSR)
   SPRs give status and control of resources within
    the processor core.
Five important user mode SPRs are:
   The Fixed-Point Exception Register (XER) is used for indicating conditions
    for integer operations, such as carries and overflows.

   The Floating-Point Status and Control Register (FPSCR) is a 32-bit register
    used to store the status and control of the floating-point operations.

   The Count Register (CTR) is used to hold a loop count that can be
    decremented during the execution of branch instructions.

    The Condition Register (CR) is a 32-bit register grouped into eight fields,
    where each field is 4 bits that signify the result of an instruction’s operation:
    Equal (EQ), Greater Than (GT), Less Than (LT), and Summary Overflow

   The Link Register (LR) contains the address to return to at the end of a
    function call.
    General Purpose Registers :

   The Architecture specifies that all implementations have
    32 GPRs (GPR0 - GPR31).

   GPRs are the source and destination of all fixed-point
    operations and load/store operations. They also provide
    access to SPRs and DCRs.

   They are all available for use in every instruction with
    one exception: In certain instructions, GPR0 simply
    means “0” and no lookup is done for GPR0’s contents.
Floating Point Registers :

   The PowerPC architecture provides thirty-two 64-bit
    floating-point registers.

Device Control Registers :

   DCRs are similar to SPRs in that they give status and
    control information, but DCRs are for resources outside
    the processor core.

   DCRs allow for memory-mapped I/O control without
    using up portions of the memory address space.
Machine State Register :
   MSR represents the state of the machine.

   It is accessed only in supervisor mode, and contains the
    settings for things such as memory translation, cache
    settings, interrupt enables, user/privileged state, and
    floating point availability. Exact control bits vary by

   The MSR does not readily fit into the SPR/DCR/GPR
    classification, as it contains its own pair of instructions to
    read and write the contents of the MSR into a GPR.
                            Data Types
   PowerPC can deal with data types of 8–bits (byte), 16-bits
    (halfword), 32-bits (word) and 64-bits (doubleword) in length. It
    can use either little-endian or big-endian style; that is, the least
    significant byte is stored in the lowest or highest address.

   Fixed-point data types include:
    * Unsigned byte
    * Unsigned halfword
    * Signed halfword
    * Unsigned word
    * Signed word
    * Unsigned doubleword
    * Byte Strings: From 0 – 128 bytes in length

   Floating-point data types include IEEE-754 single- and double-
    precision types.
                  Instruction Format

   The architecture encodes all instructions in 32 bits and
    aligns them on word address boundaries in memory.

   Instructions are first decoded by the upper 6 bits, in a
    field called the primary opcode. The remaining 26 bits
    contain operands and/or reserved fields.

   Different types of instructions defined are :
    ALU, Floating Point , Load/Store, Branch, Condition and
    Synchronization Instructions
Instruction Types
                       Addressing Modes
Three types of operand addressing :

   Memory operand addressing:
        Indirect addressing :
        * Base address in a GPR + a 16-bit sign-extended literal
        Indirect-indexed addressing :
        * Base address in a GPR + displacement from another GPR

   ALU and Floating-point instruction operand addressing:
       Three-register Format

   Branch Operand Addressing :
       Absolute : Use the literal as the absolute address.
       Relative : Use the literal as the displacement from the branch
                   instruction address.
       Indirect : Take the target address from the LR or CTR registers
              PowerPC G4e Pipelining
   Seven Stage Pipeline

   Superscalar Microprocessor – allows multiple instructions
    to be executed in parallel.

    Nine Execution Units
   BPU : Branch Processing Unit
   VPU : Vector Permute Unit
   VIU : Vector Integer Unit
   VCIU : Vector Complex Integer Unit
   VFPU : Vector Floating Point Unit
   FPU : Floating Point Unit
   IU : Integer Unit
   CIU : Complex Integer Unit
   LSU : Load/Store Unit
with emphasis on
pipeline stages of
the front end and
  the functional
            PowerPC G4e Pipeline Stages
   Stages 1 and 2 - Instruction Fetch:

       These two stages are both dedicated primarily to grabbing an
        instruction from the L1 cache.

       The G4e can fetch four instructions per clock cycle from the L1
        cache and send them on to the next stage

   Stage 3 - Decode/Dispatch:

       Once an instruction has been fetched, it goes into a 12-entry
        instruction queue to be decoded.

       The G4e's decoder can dispatch up to three instructions per
        clock cycle to the next stage.
         PowerPC G4e Pipeline Stages
   Stage 4 - Issue:

       The first queue Floating-Point Issue Queue (FIQ),
        which holds floating-point (FP) instructions that are
        waiting to be executed.

       The second is the Vector Issue Queue (VIQ), which
        holds vector operations.

       The third queue is the General Instruction Queue
        (GIQ), which holds everything else.

       Once the instruction leaves its issue queue, it goes to
        the execution engine to be executed.
         PowerPC G4e Pipeline Stages
   Stage 5 - Execute:

       The instructions can pass out-of-order from their
        issue queues into their respective functional units and
        be executed.

   Stage 6 and 7 - Complete and Write-Back :

       In these two stages, the instructions are put back into
        the order in which they came into the processor, and
        their results are written back to memory.
Inside of IBM PowerPC 405lp Processor