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MPC7457 RISC Microprocessor Hardware Specifications
MOTOROLA
Features
— 64-byte (1-MB) or 128-byte (2-MB) sectored line size
— Private memory capability for half (1 MB minimum) or all of the L3 SRAM space for a total of
1-, 2-, or 4-MB of private memory
— Supports MSUG2 dual data rate (DDR) synchronous burst SRAMs, PB2 pipelined
synchronous burst SRAMs, and pipelined (register-register) late write synchronous burst
SRAMs
— Supports parity on cache and tags
— Configurable core-to-L3 frequency divisors
— 64-bit external L3 data bus sustains 64 bits per L3 clock cycle
Separate memory management units (MMUs) for instructions and data
— 52-bit virtual address; 32- or 36-bit physical address
— Address translation for 4-Kbyte pages, variable-sized blocks, and 256-Mbyte segments
— Memory programmable as write-back/write-through, caching-inhibited/caching-allowed, and
memory coherency enforced/memory coherency not enforced on a page or block basis
— Separate IBATs and DBATs (eight each) also defined as SPRs
— Separate instruction and data translation lookaside buffers (TLBs)
– Both TLBs are 128-entry, two-way set-associative, and use LRU replacement algorithm
– TLBs are hardware- or software-reloadable (that is, on a TLB miss a page table search is
performed in hardware or by system software)
Efficient data flow
— Although the VR/LSU interface is 128 bits, the L1/L2/L3 bus interface allows up to 256 bits
— The L1 data cache is fully pipelined to provide 128 bits/cycle to or from the VRs
— L2 cache is fully pipelined to provide 256 bits per processor clock cycle to the L1 cache
— As many as eight outstanding, out-of-order, cache misses are allowed between the L1 data
cache and L2/L3 bus
— As many as 16 out-of-order transactions can be present on the MPX bus
— Store merging for multiple store misses to the same line. Only coherency action taken
(address-only) for store misses merged to all 32 bytes of a cache block (no data tenure needed).
— Three-entry finished store queue and five-entry completed store queue between the LSU and the
L1 data cache
— Separate additional queues for efficient buffering of outbound data (such as castouts and
write-through stores) from the L1 data cache and L2 cache
Multiprocessing support features include the following:
— Hardware-enforced, MESI cache coherency protocols for data cache
— Load/store with reservation instruction pair for atomic memory references, semaphores, and
other multiprocessor operations
Power and thermal management
— 1.3-V processor core
— The following three power-saving modes are available to the system:
– Nap—Instruction fetching is halted. Only those clocks for the time base, decrementer, and
JTAG logic remain running. The part goes into the doze state to snoop memory operations
on the bus and back to nap using a QREQ/QACK processor-system handshake protocol.