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ac6 >> ac6-training >> Processors >> ARM Cores >> NEON-v8 programming

RC2 NEON-v8 programming

This course explains how to use ARMv8 NEON SIMD instructions to boost multimedia algorithms

Objectives

This course has been designed for programmers wanting to run multimedia algorithms on NEON Single Instruction Multiple Data execute units on ARMv8 processors.
Evolution of the NEON architecture between ARMv7 and ARMv8 is detailed.
Each instruction family is detailed, first at assembly level, and then at C level using macros developed present in arm_neon.h file.
Several tricky usage of processing instructions are provided.
Vector and vector element load / store instructions are studied and guidelines for organizing data in memory are provided to minimize the number of memory accesses.
The underlying cache operation as well as preload mechanisms (instruction and hardware prefetch) are detailed to explain how a processing can be pipelined .
The course shows how DSP typical algorithms such as FIR and FFT can be vectorized and then optimized to be executed on NEON unit.
Cryptographic operations are also detailed, with explanation of the supported algorithms.

	Labs are compiled with GCC and run on a Linux Cortex-A53 board or a simulator
	A more detailed course description is available on request at training@ac6-training.com

Prerequisites

Knowledge of ARMv7 instruction sets.

Day 1

Introduction to NEON

Clarifying the resources shared by NEON and the scalar floating point engine
Explaining the AArch32 and AArch64 differences
NEON Register banks

S, D and Q registers (AArch32)
B, H, S, D and V registers (AArch64)

Data types
Vector vs scalar
Related system registers
Alignment issues
Enabling NEON
Differences between NEONv7 and NEONv8

NEON instruction syntax

Instructions producing wider / narrower results
Instructions modifiers
Selecting the shape
Selecting the operand / result type
Syntax flexibility
Declaring initialized vectors in C language
Using unions with vectors and arrays of vectors to simplify the debug
Casting vectors

Data transfer instructions

Move
Swap
Table lookup
Vector transpose
Vector zip / unzip
Data transfer between NEON and integer unit

Practical lab: clarifying narrow and long instructions, building a vector from bytes selected from a pair of vectors

Exercise:	Example: managing audio samples
Exercise:	Using load with de-interleaving instructions to store all right lane samples into a vector and left lane samples into another vector
Exercise:	Clarifying narrow and long instructions, building a vector from bytes selected from a pair of vectors

Arithmetic Instructions

Arithmetic instructions

Add, modulo vs saturated arithmetic
Halving / Doubling the result
Rounding
Subtract
Multiply
Multiply accumulate / Multiply subtract
Absolute value
Min / Max

Exercise:

Implementing a complex multiply accumulate with NEON

Conversion instructions

Converting Floating Point numbers into Fixed point numbers
Converting Fixed point numbers into Floating point numbers

Exercise:

Converting fixed-point elements into single precision floating point values and adding the resulting elements

Advanced arithmetic instructions

Reciprocal estimate, reciprocal square root estimate, Newton-raphson algorithm
Pairwise instructions

Day 2

Logic and Bitfield Instructions

Element comparison
Logic instructions

Logical AND, Bit Clear, OR, XOR
Operations with immediate values

Bitfield instructions

Count Leading zeros, ones, signs
Bitwise insert instructions
Conditional bitwise insert instructions, avoiding branches
Shifts with possible rounding and saturation
Bitfield reverse

Exercise:

Transposing a matrix, shifting a large bitmap using vector instructions

NEON Cryptography Extension

The Cryptography extension
Algorithms supported

AES
SHA1
SHA256

Optimizing techniques

Automatic vectorization
Tuning loops for optimal results

Avoid loop feedbacks
Avoid loop-dependent conditionals
Avoid early termination
Padding loops

Exercise:

Experimenting with loop auto-vecorization

Pointers and arrays

indirect addressing
pointer aliasing and restrict

Exercise:

Using restrict to eliminate dependencies

Function calls and inlining

promises

Exercise:

Making promises to help the compiler optimize

Avoiding data dependencies

NEON coding examples

FIR filter

Converting the scalar algorithm into a vector algorithm
Finding the NEON instructions to encode the vector algorithm
Optimizing the code
Using the performance monitor to tune the algorithm

FFT (DFT)

Converting the scalar algorithm into a vector algorithm, understanding how circle properties can be used to process 4 angles concurrently
Finding the NEON instructions to encode the vector algorithm
Optimizing the code
Using the performance monitor to tune the algorithm

This course, designed for face-to-face delivery, can be provided either in our Paris training center or, worldwide, on your premises.

Scheduled classes are confirmed as soon as there is two confirmed bookings.

To book a training session or for more information, please contact us on info@ac6-training.com.

Registrations are accepted till one week before the start date for scheduled classes. For late registrations, please consult us.

You can also fill and send us the registration form

Last update of course schedule: 10 May 2017

Booking one of our trainings is subject to our General Terms of Sales

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