Features
– Thirty-two 64-bit FPRs for single- or double-precision operands
— Four vector units and 32-entry vector register file (VRs)
– Vector permute unit (VPU)
– Vector integer unit 1 (VIU1) handles short-latency AltiVec™ integer instructions, such as vector add
instructions (vaddsbs, vaddshs, and vaddsws, for example)
– Vector integer unit 2 (VIU2) handles longer-latency AltiVec integer instructions, such as vector
multiply add instructions (vmhaddshs, vmhraddshs, and vmladduhm, for example)
– Vector floating-point unit (VFPU)
— Three-stage load/store unit (LSU)
– Supports integer, floating-point, and vector instruction load/store traffic
– Four-entry vector touch queue (VTQ) supports all four architected AltiVec data stream operations
– Three-cycle GPR and AltiVec load latency (byte, half-word, word, vector) with one-cycle
throughput
– Four-cycle FPR load latency (single, double) with one-cycle throughput
– No additional delay for misaligned access within double-word boundary
– Dedicated adder calculates effective addresses (EAs)
– Supports store gathering
– Performs alignment, normalization, and precision conversion for floating-point data
– Executes cache control and TLB instructions
– Performs alignment, zero padding, and sign extension for integer data
– Supports hits under misses (multiple outstanding misses)
– Supports both big- and little-endian modes, including misaligned little-endian accesses
•
•
Three issue queues FIQ, VIQ, and GIQ can accept as many as one, two, and three instructions, respectively,
in a cycle. Instruction dispatch requires the following:
— Instructions can be dispatched only from the three lowest IQ entries—IQ0, IQ1, and IQ2
— A maximum of three instructions can be dispatched to the issue queues per clock cycle
— Space must be available in the CQ for an instruction to dispatch (this includes instructions that are
assigned a space in the CQ but not in an issue queue)
Rename buffers
— 16 GPR rename buffers
— 16 FPR rename buffers
— 16 VR rename buffers
Dispatch unit
•
•
— Decode/dispatch stage fully decodes each instruction
Completion unit
— The completion unit retires an instruction from the 16-entry completion queue (CQ) when all
instructions ahead of it have been completed, the instruction has finished execution, and no exceptions
are pending.
— Guarantees sequential programming model (precise exception model)
— Monitors all dispatched instructions and retires them in order
— Tracks unresolved branches and flushes instructions after a mispredicted branch
MPC7455 RISC Microprocessor Hardware Specifications, Rev. 4.1
4
Freescale Semiconductor
FREESCALE [ Freescale ]
