THUMB INSTRUCTIONS SET -ARM Processors



THUMB INSTRUCTIONS SET


On execution, 16-bit Thumb instructions are transparently decompressed to full 32-bit ARM instructions in real time, without performance loss.
Thumb has all the advantages of a 32-bit core:
32-bit address space
32-bit registers
32-bit shifter, and Arithmetic Logic Unit (ALU)
32-bit memory transfer.
Thumb therefore offers a long branch range, powerful arithmetic operations, and a large address space.
Thumb code is typically 65% of the size of ARM code, and provides 160% of the performance of ARM code when running from a 16-bit memory system. Thumb, therefore, makes the ARM7TDMI core ideally suited to embedded applications with restricted memory bandwidth, where code density and footprint is important.
The availability of both 16-bit Thumb and 32-bit ARM instruction sets gives designers the flexibility to emphasize performance or code size on a subroutine level, according to the requirements of their applications. For example, critical loops for applications such as fast interrupts and DSP algorithms can be coded using the full ARM instruction set then linked with Thumb code.
Jazelle DBX (Direct Bytecode eXecution) allows some ARM processors to execute Java bytecode in hardware as a third execution state alongside the existing ARM and Thumb modes.Jazelle functionality was specified in the ARMv5TEJ architecture and the first processor with Jazelle technology was the ARM926EJ-S. Jazelle is denoted by a 'J' appended to the CPU name, except for post-v5 cores where it is required (albeit only in trivial form) for architecture conformance.
Jazelle RCT (Runtime Compilation Target) is a different technology and is based on ThumbEE mode and supports ahead-of-time (AOT) and just-in-time (JIT) compilation with Java and other execution environments.
The most prominent use of Jazelle DBX is by manufacturers of mobile phones to increase the execution speed of Java ME games and applications [citation needed]. A Jazelle-aware Java Virtual Machine (JVM) will attempt to run Java bytecodes in hardware, while returning to the software for more complicated, or lesser-used bytecode operations. ARM claims that approximately 95% of bytecode in typical program usage ends up being directly processed in the hardware.
The published specifications are very incomplete, being only sufficient for writing operating system code that can support a JVM that uses Jazelle[citation needed]. The declared intent is that only the JVM software needs to (or is allowed to) depend on the hardware interface details. This tight binding facilitates that the hardware and JVM can evolve together without affecting other software. In effect, this gives ARM Holdings considerable control over which JVMs are able to exploit Jazelle[citation needed]. It also prevents open source JVMs from using Jazelle. These issues do not apply to the ARMv7 ThumbEE environment, the nominal successor to Jazelle DBX
Electronic design automation (EDA or ECAD) is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits. The tools work together in adesign flow that chip designers use to design and analyze entire semiconductor chips.
Joint Test Action Group (JTAG) is the common name for the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture. It was initially devised by electronic engineers for testing printed circuit boards using boundary scan and is still widely used for this application.
Today, JTAG is also widely used for IC debug ports. In the embedded processor market, essentially all modern processors implement JTAG when they have enough pins. Embedded systemsdevelopment relies on debuggers communicating with chips with JTAG to perform operations like single stepping and breakpointing.

An instruction pipeline is a technique used in the design of computers to increase their instruction throughput (the number of instructions that can be executed in a unit of time). Pipelining does not reduce the time to complete an instruction, but increases instruction throughput by performing multiple operations in parallel.
Each instruction is split into a sequence of dependent steps. The first step is always to fetch the instruction from memory; the final step is usually writing the results of the instruction to processor registers or to memory. Pipelining seeks to let the processor work on as many instructions as there are dependent steps, just as an assembly line builds many vehicles at once, rather than waiting until one vehicle has passed through the line before admitting the next one. Just as the goal of the assembly line is to keep each assembler productive at all times, pipelining seeks to keep every portion of the processor busy with some instruction. Pipelining lets the computer's cycle time be the time of the slowest step, and ideally lets one instruction complete in every cycle.
The term pipeline is an analogy to the fact that there is fluid in each link of a pipeline, as each part of the processor is occupied with work
Basic five-stage pipeline in a RISC machine (IF = Instruction Fetch, ID = Instruction Decode, EX = Execute, MEM = Memory access, WB = Register write back). In the fourth clock cycle (the green column), the earliest instruction is in MEM stage, and the latest instruction has not yet entered the pipeline.
The Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters. These early machines had data storage entirely contained within the central processing unit, and provided no access to the instruction storage as data. Programs needed to be loaded by an operator; the processor could not boot itself.
Today, most processors implement such separate signal pathways for performance reasons but actually implement a modified Harvard architecture, so they can support tasks such as loading a program from disk storage as data and then executing it.
The term Von Neumann architecture, also known as the Von Neumann model or the Princeton architecture, derives from a 1945 computer architecture description by the mathematician and early computer scientist John von Neumann and others, First Draft of a Report on the EDVAC. This describes a design architecture for an electronic digital computer with subdivisions of aprocessing unit consisting of an arithmetic logic unit and processor registers, a control unit containing an instruction register andprogram counter, a memory to store both data and instructions, external mass storage, and input and output mechanisms. The meaning of the term has evolved to mean a stored-program computer in which an instruction fetch and a data operation cannot occur at the same time because they share a common bus. This is referred to as the Von Neumann bottleneck and often limits the performance of the system.
The design of a Von Neumann architecture is simpler than the more modern Harvard architecture which is also a stored-program system but has one dedicated set of address and data buses for reading data from and writing data to memory, and another set of address and data buses for fetching instructions.
A stored-program digital computer is one that keeps its programmed instructions, as well as its data, in read-writerandom-access memory (RAM). Stored-program computers were an advancement over the program-controlled computers of the 1940s, such as theColossus and the ENIAC, which were programmed by setting switches and inserting patch leads to route data and to control signals between various functional units. In the vast majority of modern computers, the same memory is used for both data and program instructions, and the Von Neumann vs. Harvard distinction applies to the cache architecture, not main memory.

In general, the noun synthesis (from the ancient Greek σύνθεσις, σύν "with" and θέσις "placing") refers to a combination of two or more entities that together form something new; alternately, it refers to the creating of something by artificial means. The corresponding verb, to synthesize (or synthesise), means to make or form a synthesis.
The ARM7TDMI processor has seven modes of operation:
User mode is the usual ARM program execution state, and is used for executing most application programs.
Fast Interrupt (FIQ) mode supports a data transfer or channel process. Interrupt (IRQ) mode is used for general-purpose interrupt handling. Supervisor mode is a protected mode for the operating system.
Abort mode is entered after a data or instruction Prefetch Abort.
System mode is a privileged user mode for the operating system.
orthogonal instruction set definition
architecture An instruction set where all (or most) instructions have the same format and all registers and addressingmodes can be used interchangeably - the choices of op code, register, and addressing mode are mutuallyindependent (loosely speaking, the choices are " orthogonal"). This contrasts with some early Intelmicroprocessors where only certain registers could be used by certain instructions.
Examples include the PDP-11680x0ARMVAX
THUMB INSTRUCTIONS SET -ARM Processors THUMB INSTRUCTIONS SET -ARM Processors Reviewed by Suresh Bojja on 9/30/2015 07:03:00 AM Rating: 5

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