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Harris Semiconductor Harris Corporation was an American technology company, defense contractor, and information technology services provider that produced wireless equipment, tactical radios, electronic systems, night vision equipment and both terrestrial and sp ...
RTX 2000, now manufactured by
Intersil Intersil is an American semiconductor company headquartered in Milpitas, California. , Intersil is a subsidiary of Renesas. The previous Intersil was formed in August 1999 through the acquisition of the semiconductor business of Harris Corpor ...
, is a
16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two ...
stack machine In computer science, computer engineering and programming language implementations, a stack machine is a computer processor or a Virtual machine#Process virtual machines, process virtual machine in which the primary interaction is moving short- ...
microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...
architecture designed for
real-time computing Real-time computing (RTC) is the computer science term for Computer hardware, hardware and software systems subject to a "real-time constraint", for example from Event (synchronization primitive), event to Event (computing), system response. Rea ...
and programmed primarily in
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotl ...
.
Radiation hardened Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environm ...
versions, the RTX 2010 series, have been used in numerous
spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...
. The original design was created by Chuck Moore, the inventor of the Forth language. In 1983 he formed Novix to design a microprocessor that could directly run the language. The NC4000 was released in June 1985, and soon renamed the NC4016. This ran at 7.5 MHz and up to 10  MIPS. An updated version, the NC5016, ran at 10 MHz and 12 MIPS, and a planned NC6016 appears not to have entered production, and Novix shut down during this period. Harris licensed the original 4016 design shortly after it was introduced, modified it, and introduced the resulting RTX line, short for "Real Time eXpress". They added several features, including on-chip
cache memory In computing, a cache ( ) is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsew ...
, a multiple/divide unit and program memory, and launched the RTX2000 in 1988, along with the RTX2001 which removed the multiplier unit. An upgrade with
input/output In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...
systems, timers and a complete
floating point unit A floating-point unit (FPU), numeric processing unit (NPU), colloquially math coprocessor, is a part of a computer system specially designed to carry out operations on floating-point numbers. Typical operations are addition, subtraction, multipli ...
became the RTX2010. All of these were produced primarily on a
silicon on sapphire Silicon on sapphire (SOS) is a hetero-epitaxial process for metal–oxide–semiconductor (MOS) integrated circuit (IC) manufacturing that consists of a thin layer (typically thinner than 0.6  μm) of silicon grown on a sapphire () wafer. S ...
line for space applications. A similar
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in a maximum of 32- bit units. Compared to smaller bit widths, 32-bit computers can perform la ...
design, the RTX 4000, was introduced in 1989, but not put into production.


Characteristics

A stack machine contrasts with traditional designs in that it lacks general purpose
processor register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-onl ...
s defined in the
instruction set architecture In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, ...
. Instead it uses
addressing mode Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how the machine language instructions ...
s based on offsets in the stack, which is normally stored in
main memory Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processin ...
or partially cached in registers that are not visible to the programmer. For example, a modern
RISC In electronics and computer science, a reduced instruction set computer (RISC) is a computer architecture designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a comp ...
processor generally includes an instruction to the effect of , which means "add the value in register A to the value in register B and place the result in register C". In a stack-based machine, this instruction would simply be , which would inherently remove the top two values on the stack, add them, and place the result back on it. One advantage of this approach is that the instructions are generally smaller; in a machine with 32 user-visible registers like many RISC systems, each of the three register references requires five bits, which demand that the instruction be at least three bytes and typically four. In a stack machine, single-byte opcodes can cover many of the instructions. Accessing parameters through a stack in main memory is slower than dedicated registers, and stack machines often have lower general purpose performance as a result. However, this is offset in certain uses. In a register machine, the values in the registers have to be saved out to memory for things like
subroutine call In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a p ...
s and
interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...
processing. If the machine has thirty-two 32-bit registers, this means 1 kbit has to be saved out and another loaded. In a stack machine there are effectively unlimited registers, and the active set can be selected by changing a single value, the
stack pointer A stack register is a computer central processor register whose purpose is to keep track of a call stack. On an accumulator-based architecture machine, this may be a dedicated register. On a machine with multiple general-purpose registers, it m ...
. This makes these systems extremely fast at
context switching In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point, and then restoring a different, previously saved, state. This allows multiple processes ...
and can offer significant performance improvements in systems with many interrupts, like
real-time computing Real-time computing (RTC) is the computer science term for Computer hardware, hardware and software systems subject to a "real-time constraint", for example from Event (synchronization primitive), event to Event (computing), system response. Rea ...
. The RTX 2000 is a two-stack machine, each stack 256 words deep, that supports direct execution of
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotl ...
. Subroutine calls only take one processor cycle and returns take zero. It also has a very low and consistent
interrupt latency In computing, interrupt latency refers to the delay between the start of an Interrupt Request (IRQ) and the start of the respective Interrupt Service Routine (ISR). For many operating systems, devices are serviced as soon as the device's interru ...
of only four processor cycles, which lends it well to realtime applications. It features multiple instruction busses that allow several instructions to be dispatched at the same time, which helps eliminate pauses while waiting on data from main memory by performing an instruction that has the data already loaded. Finally, because the instructions are directly mapped onto high-level concepts, the instruction code is very dense and programs are much smaller than normal
assembler language In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence bet ...
s used with traditional designs.


History

In 1983, Chuck Moore implemented a processor for his programming language
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotl ...
as a gate array. As Forth can be considered a dual stack virtual machine, he made the processor, Novix N4000 (later renamed NC4016), as a dual-stack
machine A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromol ...
. This system used only 4,000 gates constructed from 16,000
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...
transistors, compared to 68,000 gates for the 1979
Motorola 68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector ...
. The chip could directly execute 40 Forth primitives and 123 combinations, eliminating the need for a complete
virtual machine In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...
and speeding performance of the most common instructions. In 1988,
Harris Semiconductor Harris Corporation was an American technology company, defense contractor, and information technology services provider that produced wireless equipment, tactical radios, electronic systems, night vision equipment and both terrestrial and sp ...
purchased the rights to the Novix line and began an improvement program. They added on-chip stacks to reduce the number accesses to main memory, a number of on-chip timers and counters, a dedicated interrupt controller, and a single-cycle hardware multiplier. The new version was renamed the RTX 2000 and marketed for space applications.


Example spacecraft that use the RTX2010

*
Advanced Composition Explorer Advanced Composition Explorer (ACE or Explorer 71) is a NASA Explorer program satellite and space exploration mission to study matter comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-ti ...
(ACE) *
NEAR NEAR or Near may refer to: People * Thomas J. Near, US evolutionary ichthyologist * Near, a developer who created the higan emulator Science, mathematics, technology, biology, and medicine * National Emergency Alarm Repeater (NEAR), a form ...
/Shoemaker *
TIMED timed (time daemon) is an operating system program that maintains the system time in synchronization with time servers using the Time Synchronization Protocol (TSP) developed by Riccardo Gusella and Stefano Zatti. Gusella and Zatti had done e ...
* Rosetta's lander -
Philae The Philae temple complex (; ,  , Egyptian: ''p3-jw-rķ' or 'pA-jw-rq''; , ) is an island-based temple complex in the reservoir of the Aswan Low Dam, downstream of the Aswan Dam and Lake Nasser, Egypt. Originally, the temple complex was ...


References


External links

* Intersil's product page. * * * * * {{refend Avionics computers Radiation-hardened microprocessors Stack machines 16-bit microprocessors