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

 

Duration	Cost	Calendar
2 days	1970 € HT
Last update: 10 May 2017
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 a confirmed booking.
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