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flush-all and flush-single-entry functions, and the instruc-
tion TLB supports only the flush-all function.
Power management: All the ARM processor cores and
cached macrocells are static designs. Furthermore, the
designs use gated clocks and transparent latches, clocking
the logic only during an operation (but not during a wait
state).
Special instructions: ARM has 11 basic types of fixed-length
instructions, which execute conditionally—not just
branch—and reduce the need for short pipeline-flushing
branches. A not-taken instruction executes in one cycle.
Taken branches incur a three-cycle delay. The 16 execution-
condition codes include equal, not equal, always, negative,
and overflow. The ARM lacks explicit shift instructions;
instead, all ALU operations can perform an optional shift
operation in one execution cycle. The processors have block-
data-transfer instructions to load and store data from any
subset of the 16 general-purpose registers.
ARM processors lack an integer-divide instruction; howev-
er, the chips have multiply and multiply-accumulate (MAC)
instructions. The MAC instruction speeds math-intensive
applications. ARM processors can synthesize division and
multiplication by a constant using sequences of one or more
shift-and-add or shift-and-subtract instructions. (For exam-
ple, division by 4 and multiplication by 5 each take one
cycle.)
Special on-chip peripherals: The ARM7 Thumb and ARM9
Thumb processor cores have integrated EmbeddedICE logic,
allowing you to debug the core via a JTAG interface. The ARM
Advanced Microcontroller Bus Architecture (AMBA) interface
is the standard bus interface to ARM7 Thumb and ARM9
Thumb cached macrocells.
Development tools: ARM offers a variety of software-devel-
opment tools and hardware-development platforms, includ-
ing the ARMUlator instruction-set emulator. A range of third-
party development tools and operating systems also support
the ARM architecture. Cygnus Solutions (www.cygnus.com),
Embedded Performance (www.episupport.com), Green Hills
Software (www.ghs.com), Metaware (www.metaware.com),
Microtec (www.microtec.com), Microware Systems Corp
(www
.microware.com), and Wind River (www.windriver.
com) offer development-tool chains and compilers. Acceler-
ated Technology (www.atinucleus.com), Chorus Systems
(www.sun.com), CMX Co (www.cmx.com), Embedded Per-
formance, Etnoteam (www.etnoteam.it/), Geoworks
(www.geoworks.com), Integrated Systems (www.isi.com),
Microsoft (www.microsoft.com), Microware, Psion Software
(www.psion.com), US Software (www.uss.com), and Wind
River provide RTOS support. Hewlett-Packard (www.
hp.com), Lauterbach (www.lauterbach.com), and Yokogawa
Digital Corp (www.yokogawa.com) offer a debugger and an
in-circuit emulator.
CIRCL
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ARM processors (continued)
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