DESCRIPTION
The ACT5231 is a highly integrated superscalar
microprocessor that implements a superset of the
MIPS IV Instruction Set Architecture(ISA). It has a
high performance 64-bit integer unit, a high
throughput, fully pipelined 64-bit floating point unit,
an operating system friendly memory management
unit with a 48-entry fully associative TLB, a 32KB
2-way set associative instruction cache, a 32KB
2-way set associative data cache, and an efficient
32-bit system interface. The ACT5231 can issue
both an integer and a floating point instruction in the
same cycle.
The ACT5231 is ideally suited for high-end
embedded
control
applications
such
as
internetworking,
high
performance
image
manipulation, high speed printing, and 3-D
visualization.
Integer Unit
The ACT5231 implements the MIPS IV
Instruction Set Architecture, and is therefore fully
upward compatible with applications that run on
processors implementing the earlier generation
MIPS I-III instruction sets. Additionally, the
ACT5231 includes two implementation specific
instructions not found in the baseline MIPS IV ISA
but that are useful in the embedded market place.
Described in detail in the QED RM5231 datasheet,
these instructions are integer multiply-accumulate
and 3-operand integer multiply.
The ACT5231 integer unit includes thirty-two
general purpose 64-bit registers, a load/store
architecture with single cycle ALU operations (add,
sub, logical, shift) and an autonomous multiply/
divide unit. Additional register resources include:
the HI/LO result registers for the two-operand
integer multiply/divide operations, and the program
counter(PC).
HARDWARE OVERVIEW
The ACT5231 offers a high-level of integration
targeted
at
high-performance
embedded
applications. The key elements of the ACT5231 are
briefly described below.
Register File
The ACT5231 has thirty-two general purpose
registers with register location 0 hard wired to zero.
These registersich allo are used for scalar integer
operations and address calculation. The register
file has two read ports and one write port and is fully
bypassed to minimize operation latency in the
pipeline.
Superscalar Dispatch
The ACT5231 has an efficient asymmetric
superscalar dispatch unit which allows it to issue an
integer instruction and a floating-point computation
instruction simultaneously. With respect to
superscalar issue, integer instructions include alu,
branch, load/store, and floating-point load/ store,
while floating-point computation instructions
include floating-point add, subtract, combined
multiply-add, converts, etc. In combination with its
high throughput fully pipelined floating-point
execution unit, the superscalar capability of the
ACT5231 provides unparalleled price/performance
in
computationally
intensive
embedded
applications.
ALU
The ACT5231 ALU consists of the integer adder/
subtractor, the logic unit, and the shifter. The adder
performs address calculations in addition to
arithmetic operations, the logic unit performs all
logical and zero shift data moves, and the shifter
performs shifts and store alignment operations.
Each of these units is optimized to perform all tions
in a single processor cycle.
CPU Registers
Like all MIPS ISA processors, the ACT5231 CPU
has a simple, clean user visible state consisting of
32 general purpose registers, two special purpose
registers for integer multiplication and division, a
program counter, and no condition code bits.
For additional Detail Information regarding the
operation of the Quantum Effect Design (QED)
RISCMark™ RM 5231™, 32-Bit Superscalar
Microprocessor see the latest QED datasheet.
Pipeline
For integer operations, loads, stores, and other
non-floating-point operations, the ACT5231 uses
the simple 5-stage pipeline also found in the
ACT52xx family, R4600, R4700, and R5000. In
addition to this standard pipeline, the ACT5231
uses an extended seven stage pipeline for
floating-point operations. The ACT5231 does
virtual to physical translation in parallel with cache
access.
Aeroflex Circuit Technology
2
SCD5231 REV 1 12/22/98 Plainview NY (516) 694-6700
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
