Category Archives: Design Issues

Introduction to the ARM® Cortex®-M7 Cache – Part 3 Optimising software to use cache

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

Caches – Why do we miss?
Cold Start

As stated, both data and instruction caches are required to be invalidated on system start. Therefore, the first load of any object (code or data) cannot be in cache (thus the cold start condition).

One available technique to help with cold-start conditions is the ability to pre-load data into the cache. The ARMv7-M instruction set adds the Preload Data (PLD) instruction. The PLD instruction signals to the memory system that data memory accesses from a […]

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Introduction to the ARM® Cortex®-M7 Cache – Part 2 Cache Replacement Policy

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

Instruction Cache Replacement Policy

Starting with the simpler instruction cache case; when we encounter a cache miss the normal policy is to evict the current cache line and replace it with the new cache line. This is known as a read-allocate policy and is the default on all instruction caches.

Cold start (first read)

It should also be noted that on system power-up the initial state of the cache is unknown. On the ARMv7-M all caches are disabled at reset. Before the cache […]

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Introduction to the ARM® Cortex®-M7 Cache – Part 1 Cache Basics

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

For many years, the majority of smaller microprocessor-based systems have typically not used caches. With the launch of the ARMv7 architectures, caches were supported in the ARMv7-A family (e.g. Cortex-A8, etc.) but not supported in the core design of the ARMv7-M micro-controllers such as the Cortex-M3 and Cortex-M4. However, when the Cortex-M7 was announced, it broke that mould by offering cache support for the smaller embedded micro-controller.

This series is broken down in three parts:

Basic principles of cache
Cache replacement policies
Optimising software […]

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Practice makes perfect, part 3 – Idiomatic kata

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

Previously, we looked at some of the foundational C++ code kata – that is, elements of C++ coding that are absolutely key to master if you’re going to be programming in C++.
Practice makes perfect, part 1 – Code kata
Practice makes perfect, part 2 – foundation kata

In this article I want to introduce what I call ‘idiomatic’ kata.  These exercises have a bit more latitude (and variation) in how they can be implemented.  In that respect they are closer to traditional […]

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Practice makes perfect, part 2 – foundation kata

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

In the previously article we looked at the need for repetitive practice – code kata.  In this article I want to  present some of my preferred foundational kata.

If you’re a beginner to C++ I recommend you fully internalize all these examples before having a look at the idiomatic kata.

If you’re a more experienced C++ programmer you may be looking at these kata and thinking “Jeez – these are so basic!  Who couldn’t do this!”.  Bear in mind though – we […]

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Practice makes perfect, part 1 – Code kata

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

Imagine you’re at a Jazz club, enjoying a smooth jazz quartet.  It’s time for the sax player’s solo.  All of a sudden, he stops the band, rifles in a bag a pulls out a book of music theory.

“What the?!” you think.

The saxophonist looks to the audience, “I’ve just got to look up the notes for E-flat minor.  I can never remember them.”

It’s understandable you’re unlikely be too impressed with this particular musician.

If you’re a musician, a sportsperson, a dancer, martial […]

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Celebrating 10 years – my top 10 blog articles

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

It’s difficult to believe we’ve been writing articles for 10 years.  In that time I’ve written over 90 technical articles on C, C++ and embedded system design.

To celebrate I’ve picked my ‘Top 10’ articles, with a little background into why I enjoyed writing them so much, or the story behind them.

So, sit back, cue up “At the Sign of the Swinging Cymbal“* and enjoy.

 

(* This really dates

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An Introduction to Docker for Embedded Developers – Part 1 Getting Started

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

Docker is a relatively new technology, only appearing just over four years ago. The core building blocks have always been part of Unix; but the significant support, Linux containers (LCX), first appeared back in 2008.

Initially Docker was only supported on Linux, but more recently native support for OSX (my development OS of choice) and Windows (albeit Windows 10 Pro) suddenly opens up some interesting workflow choices.

The “What”

So, first, what is Docker? I’m always trying to find the right words here […]

Posted in Agile, Design Issues, Testing | 6 Comments

Making things do stuff – Part 9

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

As a final instalment in this series on hardware manipulation I thought I’d revisit read-only and write-only register types.

Using tag dispatch is not the only way to solve the read- or write-only Register problem.  For completeness let’s explore two other alternatives – SFINAE and constexpr if.

For these examples I’m going to use a simplified version of our Register class.  I’m ignoring the bit proxy class and using a reduced API.  Once understood, the techniques below can be applied to these […]

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Making things do stuff – Part 3

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

Previously, we’ve looked at the basics of hardware manipulation in C++ and applied that to a simple GPIO implementation.

In this article we’re going to have a look at encapsulating our code in a class and look at some of the design choices we have to make.

If you’re not familiar with hardware manipulation in C++ I’d highly recommend reading the previous articles in this series before continuing.

Even if you’re familiar with the concepts of hardware manipulation, if you haven’t read the […]

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