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Questions tagged [instruction-set]

Use for questions related to Instruction Set Architectures, ISA. For questions related to the inner workings of a CPU, use [cpu-architecture] instead.

An instruction set is a specification for a set of machine-readable instructions, or CPU instructions. An instruction set exists for all processing units including Graphics Processing Cores, Networking Card Processors as well at the CPU. The phrase "Instruction Set" usually implies the CPU type.

Each digital logic process which a processor can perform has an binary instruction code which caused the CPU to execute that exact instruction. An assembly language translates mnemonics into instruction codes. Instruction codes are likely to differ between different processor architectures. For example, the x86_64 instruction set for Intel CPU's includes additional 64 bit instructions (among others) for manipulating data 64 bits wide inside the CPU's core, which is an extension to the x86 32 bit capabilities of previous Intel CPU generations.

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ARM: Why only 12 bits for immediate constants?

what does it mean : I have only 12 bits for immediate constants, so can I represent immediate constants only from 0 to 2^12 = 4096 ? Operand 2 , if it's a register, can have 32 bits, but why only 12 bits for immediate constants? Where does this…
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Importance of Q(Saturation Flag) in ARM

I want to understand the importance of Q flag in ARM Processor. I know there are certain instructions like QADD,QSUB etc. But I need to understand this with some examples which will clarify the concept.
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Instruction set - Decode opcode

I'm trying to understand how the /d affects the opcode. Example: FF /6 PUSH r/m16 M Valid Valid Push r/m16. How meaning is expressed? Can anyone give me an example of the difference? Thanks!
user2622189
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What type of machine language do PCs generally run on

I've recently begun researching what it would take to program a JIT compiler. I've been studying on machine language, but I haven't been able to find what type of machine languages most standard PCs run on. I found this PDF which seems to explain a…
Codesmith
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Trouble understanding GPU disassembly

I'm trying to write a raycasting shader in GLSL, and it's being unbearably slow. So I installed AMD's "GPU Shader Analyzer", so I can look at what is actually generated. I've got it from 2 FPS up to 12, but that's still not fantastic. I feel like I…
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".long ." What does it mean in arm assembly coding?

I was going through arch/arm/head.S and found below code __turn_mmu_on_loc: .long . .long __turn_mmu_on .long __turn_mmu_on_end I am not able to understand ".long ."?
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"Read a byte from an I/O port" vs. "Read a byte from an address of memory"?

For simplifying discussion, I assume there is only one executing thread. The following are just my wild speculations: 1, If the CPU reads a byte from an address of memory, then it can repeatedly read the same value from the same address. 2, If the…
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NVidia`s ISA language

AMD defines for each GPU family ot its ISA. As I understand, ISA is a instruction set architecture : assembly -like "language". How is called NVidia`s GPU "assembly -like language"? - PTX? Is there any tool like AMD or Intel offline compiler which…
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Remote SQL Server 2008 Management Studio is not connecting

Remote SQL Server 2008 Management Studio is not connecting to the database using TMG SERVER 2010. Error 40 and 53 are showing up. But it is working without tmgserver. Please advise. Thanks
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OS privilege levels vs Hardware privilege levels

What is the difference between OS privilege levels and privilege levels of the underlying hardware? Do all system calls cause a trap to the kernel? Why do system calls cause a trap? Is it because of privileged instructions such as IN in their…
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CISC instruction length

I was wondering, what is the maximum possible length of a CISC instruction on most of today's CISC architectures? I haven't found the definitive answer yet, but it is suggested that it's 16 bytes long, in theory. In the video @ around 15:00 mins,…
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What is the rationale behind the CPU instruction set, in general and for x86's SETCC?

While examining the instruction set for Intel x86 processors I noticed there are 'intuitive' instructions like 'mov', 'add', 'mul' ... while others seem a bit unnatural like 'sete'. The question is more out of curiosity rather than practical…
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Computer architecture homework - instruction operands

A digital computer has a memory unit with 32 bits per word. The instruction set consists of 150 different operations. All instructions have an operation code part (opcode), a register operand part (specifying one of 10 different registers) and a…
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Assembly language instructions implementation

Is there some information source or technical draft (something like RFC for networking) describing implementation of particular instructions (e.g. mov, jmp, je, jle, inc, ...) for Intel architecture? Some general talk is on wikipedia but I'd like to…
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What is the actual difference between x86 floating-point and integer instruction types?

There are two fundamental types of microprocessor instructions: integer and floating-point. Accordingly, they are executed on an Integer Processing Unit and on a Floating-Point Processing Unit. That makes sense, right? But what tells the processor…
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