Features

This section summarizes features of the MPC750’s implementation of the PowerPC architecture. Major

features of the MPC750 are as follows:

• Branch processing unit

— Four instructions fetched per clock

— One branch processed per cycle (plus resolving 2 speculations)

— Up to 1 speculative stream in execution, 1 additional speculative stream in fetch

— 512-entry branch history table (BHT) for dynamic prediction

— 64-entry, 4-way set associative branch target instruction cache (BTIC) for eliminating branch

delay slots

• Dispatch unit

— Full hardware detection of dependencies (resolved in the execution units)

— Dispatch two instructions to six independent units (system, branch, load/store, fixed-point unit

1, fixed-point unit 2, or floating-point)

— Serialization control (predispatch, postdispatch, execution serialization)

• Decode

— Register file access

— Forwarding control

— Partial instruction decode

• Load/store unit

— One cycle load or store cache access (byte, half-word, word, double-word)

— Effective address generation

— Hits under misses (one outstanding miss)

— Single-cycle misaligned access within double word boundary

— Alignment, zero padding, sign extend for integer register file

— Floating-point internal format conversion (alignment, normalization)

— Sequencing for load/store multiples and string operations

— Store gathering

— Cache and TLB instructions

— Big- and little-endian byte addressing supported

— Misaligned little-endian support in hardware

• Fixed-point units

— Fixed-point unit 1 (FXU1)—multiply, divide, shift, rotate, arithmetic, logical

— Fixed-point unit 2 (FXU2)—shift, rotate, arithmetic, logical

— Single-cycle arithmetic, shift, rotate, logical

— Multiply and divide support (multi-cycle)

— Early out multiply

• Floating-point unit

— Support for IEEE-754 standard single- and double-precision floating-point arithmetic

— 3 cycle latency, 1 cycle throughput, single-precision multiply-add

— 3 cycle latency, 1 cycle throughput, double-precision add

— 4 cycle latency, 2 cycle throughput, double-precision multiply-add

— Hardware support for divide

— Hardware support for denormalized numbers

— Time deterministic non-IEEE mode

• System unit

— Executes CR logical instructions and miscellaneous system instructions

— Special register transfer instructions

• Cache structure

— 32K, 32-byte line, 8-way set associative instruction cache

— 32K, 32-byte line, 8-way set associative data cache

— Single-cycle cache access

— Pseudo-LRU replacement

— Copy-back or write-through data cache (on a page per page basis)

— Supports all PowerPC memory coherency modes

— Non-blocking instruction and data cache (one outstanding miss under hits)

— No snooping of instruction cache

• Memory management unit

— 128 entry, 2-way set associative instruction TLB

— 128 entry, 2-way set associative data TLB

— Hardware reload for TLBs

— 4 instruction BATs and 4 data BATs

— Virtual memory support for up to 4 exabytes (252) of virtual memory

— Real memory support for up to 4 gigabytes (232) of physical memory

• Level 2 (L2) cache interface (not implemented on MPC740)

— Internal L2 cache controller and 4K-entry tags; external data SRAMs

— 256K, 512K, and 1 Mbyte 2-way set associative L2 cache support

— Copy-back or write-through data cache (on a page basis, or for all L2)

— 64-byte (256K/512K) and 128-byte (1-Mbyte) sectored line size

— Supports flow-through (reg-buf) synchronous burst SRAMs, pipelined (reg-reg) synchronous

burst SRAMs, and pipelined (reg-reg) late-write synchronous burst SRAMs

— Core-to-L2 frequency divisors of ÷1, ÷1.5, ÷2, ÷2.5, and ÷3 supported

• Bus interface

— Compatible with 60x processor interface

— 32-bit address bus

— 64-bit data bus

— Bus-to-core frequency multipliers of 3x, 3.5x, 4x, 4.5x, 5x, 5.5x, 6x, 6.5x, 7x, 7.5x, 8x

supported

• Integrated power management

— Low-power 2.6/3.3-volt design

— Three static power saving modes: doze, nap, and sleep

• Integrated Thermal Management Assist Unit

— On-chip thermal sensor and control logic

— Thermal Management Interrupt for software regulation of junction temperature.

• Testability

— LSSD scan design

— JTAG interface

• Reliability and serviceability—Parity checking on 60x and L2 cache buses