Taking
advantage of the fact that they make it easier to develop software
programs with fewer bugs, Java chips are aiming at embedded
microcontrollers.
Java is attracting attention as a means of changing the World Wide
Web (WWW) Internet information browsing service into an interactive
information processing service1). Java is an
object-oriented programming language developed by Sun Microsystems,
Inc of the US, but Java application fields are extending far beyond
the Internet (Fig 1). One of the
most exciting applications is embedded systems.
Sun Microelectronics, which is the integrated circuit (IC)
development arm of Sun Microsystems, is developing Java chips for
embedded applications. They will be capable of high-speed execution
of programs described in the Java language.
Other IC manufacturers are also beginning to develop Java chips.
Mitsubishi Electric Corp of Japan announced in May 1996 that it will
port Java to its 32-bit microcontroller M32R/D for embedded
applications (Fig 2). The M32R/D
has 2 Mbytes of internal DRAM, which can be used to store the
interpreter and microkernel needed to execute Java programs.
Mitsubishi Electric says it had Java in mind when it determined the
DRAM capacity for the M32R/D.
Three Sun Java Chips
Sun Microelectronics is developing three types of Java chips
(Table 1): the picoJAVA with only
the central processing unit (CPU core); microJAVA, a microprocessor
or microcontroller consisting of picoJAVA coupled with a DRAM
controller; and the UltraJAVA high-end processor handling multimedia
instructions2).
Both microJAVA and UltraJAVA will be marketed by Sun, while
picoJAVA is slated to be licensed to semiconductor and consumer
electronics manufacturers. "We hope to license picoJAVA to ten firms
worldwide," says Chet Silvestri, president of Sun Microelectronics.
NEC Corp and Mitsubishi Electric are two such licensees, and
Toshiba Corp and Fujitsu Ltd, all of Japan, are currently in
negotiations, according to industry sources. In Korea, LG
Semiconductor and Samsung Electronics Co, Ltd will be licensed.
Semiconductor manufacturers licensed for picoJAVA will develop
chips offering high performance on a par with UltraJAVA, utilizing
superscalar architecture and other means.
Safely Embeddable Software
The reason Java chips are attracting so much attention is that the
industry believes they can resolve many of the problems that embedded
control software development face today. Engineers involved in this
type of development are becoming increasingly sensitive to reducing a
program's internal bugs; in other words, maximizing productivity and
safety.
Until lately, design has assigned top priority to performance and
object code size. As semiconductor technology progresses, performance
has risen considerably, and the restraints on object code size have
not been so tight as they used to be, thanks to increasing memory
capacity.
Today, embedded application developers are more worried about how
to make an environment that will get the product out the door
quicker, with fewer bugs. "It looks like the Java language can meet
many of these needs," one microprocessor design engineer at a major
semiconductor manufacturer pointed out.
A software engineer added, "Because productivity is emphasized, it
is likely to see widespread adoption of C++ as a development language
for embedded systems. C++ is pretty tough for electronics engineers,
however, who are experts when it comes to their equipment but not
when it comes to programming software. Java is easier to understand
than C++, and much easier for electronics engineers to utilize."
Originally for Embedded Units
The Java language was originally developed for embedded use in
electronic equipment for the end-user, like personal digital
assistants (PDA). It was also a program execution
environment3). Java is still quite suitable for these
needs. Java makes it easy to develop relatively bug-free programs
because even when the programs are used with different
microprocessors or operating systems (OS), they do not have to be
recompiled. This feature was designed in specifically with an eye
toward embedded applications.
OS and microprocessors used in embedded systems depend on cost and
performance, and there is no assurance that an embedded system may
use a microprocessor supporting the same instruction set as previous
systems. Effective utilization of past resources means that developed
software should be as independent of the microprocessor and OS as
possible.
Software in products like consumer electronics, printers and
facsimiles cannot be easily upgraded. It is possible for a
serviceperson to go to the site and rewrite the software, but that
consumes time and cost. It would be better to develop high-quality
software from the start, with fewer bugs. And that is where the
characteristics of Java come into play.
Separating Hardware, Software
From the viewpoint of the microprocessor designers, Java is
attractive because it clearly separates hardware from software.
Until now, microprocessors have been speeded up by implementing
the instruction set in the IC, and optimizing the compiler. The two
are closely linked, however, and if a new technique is introduced in
the implementation, the optimization method changes. For example,
there is an optimization method called register renaming, which the
hardware executes invisibly from the software. This means that the
optimized code for a microprocessor may actually run slower when the
microprocessor is changed. A microprocessor engineer says, "Java
chips clearly define what is hardware and what is software so each
can be optimized independently."
Stacked Architecture Adopted
Programs described in the Java language are compiled into byte
code by the Java compiler. Byte code is binary code which can be
executed on the Java virtual machine (Java VM).
This virtual computer has no registers, and all data processing
and calculations are handled through the stack. In short, it is a
"stack machine."
Close to Compiler Intermediate Code
The reason the Java VM adopted a stack-type architecture is
because it is a natural choice for a programming language compiler.
Most compilers convert the source programs into intermediate code,
and then convert the intermediate code into code designed for the
target processor (Fig 3). This
makes it easier to design compilers which will work with multiple
processors or languages.
Intermediate code usually takes the form of storing data to the
stack, and implementing various processing on it4). Stacks
are used instead of registers, making the code independent of
processor architecture. Java byte code takes the intermediate code
generated by the compiler and uses it, without changes, as the
instruction set specification.
Ample Performance Even with Stacks
The Java chip is a microprocessor which integrates essentially all
of the functions used by the Java VM. For that reason, the basic
architecture is stacked. The hardware uses registers to implement
stacks. Stack machines have been proposed in the past, but never
entered practical use because of low performance.
People in the know, however, say the Java chip has no performance
problems.
"It is quicker to use microJAVA than to execute a Java program on
a Java interpreter having a 100MHz Pentium processor," says Raj
Parekh, vice president in charge of technology at Sun
Microelectronics.
A microprocessor designer says, "With 0.35µm rule IC
manufacturing technology, it is pretty simple to get picoJAVA to run
at 100 to 200MHz. Even if a little overhead in object-oriented
language execution is added, it should be an easy matter to maintain
high performance. Although it is a stack machine, not everything is
implemented in stacks; registers are used as well. The fewer
architecture restrictions provide extra freedom in register naming,
and make it possible to use technologies gained through RISC design.
It leaves the engineer plenty of room to find elegant solutions."
224 Instructions Supported
There are 203 Java VM instructions, or a total of 224 when hidden
instructions are added in. Depending on their usage, they can handle
quite complex processing. However, not everything can be implemented
with wired logic.
"First the instructions are integrated on a chip through
microcode. Traps are generated for complex instructions that are
difficult to implement with microcode, and the instructions are
executed by software emulation," explains Parekh.
Java chips also offer extended Java byte code instructions. This
is because the instruction sets defined in the virtual machine cannot
implement all needed processing; concretely, instructions which
directly operate hardware. Parekh says, "Driver software for
transmission control protocol/Internet protocol (TCP/IP), for
example, cannot be described with Java VM instructions alone. These
instructions cannot be used in the application software."
Seeking Optimum Application
Java chips are attracting considerable attention in and out of the
industry, but at the same time there really aren't any applications
they are ideal for. A Japanese microprocessor designer comments,
"Existing microprocessors can be evaluated through MIPS ratings and
SPEC benchmarks. There are no evaluation criteria for Java chips, so
it is impossible to say what they are suited for. The documentation
seems to indicate the chip is slightly more complex than an 80386,
but there are many questions that cannot be answered until we
actually make it. The first step will probably be to form a test
element group (TEG) for evaluation."
At present, there seem to be few applications suitable for Java
chips: the only one that comes to mind is the Java Client
(Fig 4), an Internet terminal being
developed by Sun Microsystems.
Another possibility is a Java printer, using Java language instead
of the current PostScript page description language. The printer may
print out figures and text drawn by Java. Because the Java chip is
less expensive than the PostScript microprocessor, it would mean less
expensive printers.
Parekh at Sun Microelectronics also suggests game systems as an
UltraJAVA application. "UltraJAVA can play back voice and motion
video, along with three dimensional graphics, at higher speed," he
says. "It can be made cheaper than a reduced instruction set computer
(RISC)-based processor incorporating Java extended functions."
All of these applications can also be implemented without the Java
chip, of course, and none of them has anything to do with machine
control. As one software engineer puts it, "The Java chip is suited
to information-processing applications like Java clients and PDA, but
not to controlling hardware. Using Java byte code for modem control
would be pretty tough."
Demand for Low Cost
Some people in the industry feel that Java chips could only be
used in embedded control. If Java achieves widespread usage, then it
is likely that general-purpose RISC processors will incorporate the
so-called Java Extension to allow them to execute Java at high speed.
"The general-purpose RISC processor is better suited to
information processing," explains a microprocessor designer. "These
chips will soon incorporate functions for high-speed execution of
Java, and probably at low prices. The only way for the Java chip to
survive might be as a central processing unit (CPU) core for a system
controller IC."
A software engineer at a semiconductor firm added, "If it can't be
made cheaply, there's no point in making it. It is likely that
applications demanding high performance will use RISC processors, and
price-driven applications will use Java chips. The US$500 terminal is
the threshold, with Java below that line and RISC above."
by Tatsuro Hokugo
References:
1) Hokugo, T, "Sun's Java Expected to Pose Threat to
Microsoft", Nikkei
Electronics (in Japanese), no 658, pp
205-221, March 25 1996.
2) Asami, N, "Sun Microsystems Develops Stack MPU
with Java Language",
ibid, no 656, p13,
February 26 1996.
3) Van Hoff, A, Shaio, S and Starbuck, O,
Hooked on JAVA,
Addison-Wesley Publishing, 1996.
4) Aho, A, Sethi, R, and Ullman, J,
Compilers Principles, Techniques, and
Tools, Addison-Wesley Publishers Ltd,
1986.
