Add R2 to R1 and put it (the result) in R0. This is the typical way to read an assembly instruction. The ADD instruction (covered in the section below) adds R2 to R1 and puts the result in register R0 (see the previous article for an explanation of these denotations). These are typically destination and source operands, as seen below. Following the mnemonic are the operands that will be operated on. How to Read Assembly Instructions: Mnemonics and OperandsĮvery instruction begins with a mnemonic that represents an operation. And don't be afraid to dig through the ARM manual for more information. Notice it's the opcode that determines the operation-such as addition, subtraction, or exclusive OR-that the processor will perform.Īs you go through the instructions below, we'll reference Figure 1 and try to see how the assembly instruction gets encoded into binary. The opcode is 4 bits wide and sits between the immediate flag, which signals that operand 2 holds an immediate value, and the condition-set flag, which we can use to update the status register during an operation (more on these later). The condition field is 4 bits wide, as there are roughly fifteen conditional codes. ARM data-processing instructionįigure 1 shows the 32 bits found in an ARM data-processing instruction each bit has a specific purpose, either individually or as part of a group. Since most of the instructions we'll go over are for data operations, I've grabbed the data-processing instruction out of the ARMV7 manual.įigure 1. Instructions are used by the processor-let's take one look at the machine code that the instructions represent. A Rundown of x86 Processor Architecture.The Electrical Engineer’s Guide to Instruction Set Architectures ( ISAs ).What Is a Microarchitecture? Understanding Processors and Register Files in an ARM Core.Note: Later versions of the Raspberry Pi, running Raspbian, use a 64-bit ARMv8 processor, but run it in 32-bit mode just like the older v7 versions. In this article, we will focus our attention on 32-bit ARMv7 instructions and 32-bit registers. This information will be used in the next article to program a Raspberry Pi, which uses a 32-bit ARM core. We will pick up from a previous post on ARM register files-please consider reviewing that information before continuing as we will reference register denotations and register flags in the instructions below. This article is intended to help you learn about basic assembly instructions for ARM core programming. Learn some basic instructions used in the ARM instruction set used for programming ARM cores.
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