Features
This section summarizes features of the 603’s implementation of the PowerPC architecture. Major features
of the 603 are as follows:
• High-performance, superscalar microprocessor
— As many as three instructions issued and retired per clock
— As many as five instructions in execution per clock
— Single-cycle execution for most instructions
— Pipelined FPU for all single-precision and most double-precision operations
• Five independent execution units and two register files
— BPU featuring static branch prediction
— A 32-bit IU
— Fully IEEE 754-compliant FPU for both single- and double-precision operations
— LSU for data transfer between data cache and GPRs and FPRs
— SRU that executes condition register (CR) and special-purpose register (SPR) instructions
— Thirty-two GPRs for integer operands
— Thirty-two FPRs for single- or double-precision operands
• High instruction and data throughput
— Zero-cycle branch capability (branch folding)
— Programmable static branch prediction on unresolved conditional branches
— Instruction fetch unit capable of fetching two instructions per clock from the instruction cache
— A six-entry instruction queue that provides lookahead capability
— Independent pipelines with feed-forwarding that reduces data dependencies in hardware
— 8-Kbyte data cache—two-way set-associative, physically addressed; LRU replacement
algorithm
— 8-Kbyte instruction cache—two-way set-associative, physically addressed; LRU replacement
algorithm
— Cache write-back or write-through operation programmable on a per page or per block basis
— BPU that performs CR lookahead operations
— Address translation facilities for 4-Kbyte page size, variable block size, and 256-Mbyte
segment size
— A 64-entry, two-way set-associative ITLB
— A 64-entry, two-way set-associative DTLB
— Four-entry data and instruction BAT arrays providing 128-Kbyte to 256-Mbyte blocks
— Software table search operations and updates supported through fast trap mechanism
— 52-bit virtual address; 32-bit physical address
• Facilities for enhanced system performance
— A 32- or 64-bit split-transaction external data bus with burst transfers
— Support for one-level address pipelining and out-of-order bus transactions
— Bus extensions for direct-store operations
• Integrated power management
— Low-power 3.3 volt design
— Internal processor/bus clock multiplier that provides 1/1, 2/1, 3/1 and 4/1 ratios
— Three power saving modes—doze, nap, and sleep
— Automatic dynamic power reduction when internal functional units are idle
• In-system testability and debugging features through JTAG boundary-scan capability