Surprising Linux Real Time Scheduler Behavior

Matthew Eshleman November 5, 2016

I have recently been helping with embedded software design and development for a data acquisition and visualization device. The software executes within an embedded Linux context and consists of various animated user interfaces rendering the acquired data.

The data is received via a UART and a SPI connection. During project development we noticed poor UART data latency issues during heavy user interface animations. For this product to properly meet its acquisition requirements, the UART...


Favorite Tools - Look Up Tables

Matthew Eshleman October 22, 20163 comments

As we grow in our engineering careers, we must continually add new tools to our collective tool kits. One favorite tool in my toolkit will be obvious to many experienced embedded software engineers. I still remember learning this approach early in my career via code written by colleague David Starling. The tool in question: 

Look up tables 

Look up tables simplify code and improve firmware maintenance. What is a look up table? A look up table is often nothing more complex than a...


From bare-metal to RTOS: 5 Reasons to use an RTOS

Jacob Beningo October 18, 20167 comments

Developers can come up with amazing and convoluted reasons to not use an RTOS. I have heard excuses ranging from they are too expensive (despite open source solutions) all the way to they aren’t efficient and use too much memory. In some circumstances some excuses are justified but there are many reasons why a developer should look to an RTOS to help with their real-time scheduling needs.

From bare-metal to RTOS Quick Links
  • Part 1: 

Best Firmware Architecture Attributes

Dr. Tayyar GUZEL June 4, 20166 comments

Architecture of a firmware (FW) in a way defines the life-cycle of your product. Often companies start with a simple-version of a product as a response to the time-to-market caveat of the business, make some cash out of the product with a simple feature set. It takes only less than 2-3 years to reach a point where the company needs to develop multiple products derived from the same code base and multiple teams need to develop...


Modern Embedded Systems Programming: Beyond the RTOS

Miro Samek April 27, 20167 comments

An RTOS (Real-Time Operating System) is the most universally accepted way of designing and implementing embedded software. It is the most sought after component of any system that outgrows the venerable "superloop". But it is also the design strategy that implies a certain programming paradigm, which leads to particularly brittle designs that often work only by chance. I'm talking about sequential programming based on blocking.

Blocking occurs any time you wait explicitly in-line for...


Embedded Firmware Refactoring, Optimisation and Migration

Ian Smith March 29, 2016

Legacy products are often based on older hardware platforms which often become under-powered or run out of memory which constrains further product development. Customers are always looking for new features and improved performance but often either don’t want to invest in new hardware or need to retain the current field population of devices.

These are ongoing challenges for any product manufacturer, but are particularly highlighted in embedded systems where product...


Cutting Through the Confusion with ARM Cortex-M Interrupt Priorities

Miro Samek February 26, 2016

The insanely popular ARM Cortex-M processor offers very versatile interrupt priority management, but unfortunately, the multiple priority numbering conventions used in managing the interrupt priorities are often counter-intuitive, inconsistent, and confusing, which can lead to bugs. In this post I attempt to explain the subject and cut through the confusion.

The Inverse Relationship Between Priority Numbers and Urgency of the Interrupts

The most important fact to know is that ARM...


Cortex-M Exception Handling (Part 2)

Ivan Cibrario Bertolotti February 1, 20169 comments

The first part of this article described the conditions for an exception request to be accepted by a Cortex-M processor, mainly concerning the relationship of its priority with respect to the current execution priority. This part will describe instead what happens after an exception request is accepted and becomes active.

PROCESSOR OPERATION AND PRIVILEGE MODE

Before discussing in detail the sequence of actions that occurs within the processor after an exception request...


Analyzing the Linker Map file with a little help from the ELF and the DWARF

Govind Mukundan December 27, 201520 comments

When you're writing firmware, there always comes a time when you need to check the resources consumed by your efforts - perhaps because you're running out of RAM or Flash or you want to optimize something. The map file generated by your linker is a useful tool to aid in the resource analysis. I wanted to filter and sort the data generated in an interactive way so I wrote a C# WinForms application that reads the data from the map and presents it in a list view (using the awesome


Cortex-M Exception Handling (Part 1)

Ivan Cibrario Bertolotti November 28, 20152 comments

This article describes how Cortex-M processors handle interrupts and, more generally, exceptions, a concept that plays a central role in the design and implementation of most embedded systems. The main reason of discussing this topic in detail is that, in the past few years, the degree of sophistication (and complexity) of microcontrollers in handling interrupts steadily increased, bringing them on a par with general-purpose processors.


Coding Step 2 - Source Control

Articles in this series:

When I first started out in programming, version control was not an introductory topic. Not in the least because it required a 'server' (ie, a computer which a teenaged me couldn't afford) but because it seemed difficult and only useful to teams rather than...


Using XML to describe embedded devices (and speak to them)

Martin Strubel October 12, 20111 comment

This article discusses one of the typical development cycles in embedded device and communication design and presents a possible, light weight solution using the free DClib/netpp framework.

The challenge

Assume we're faced with the design of an embedded device, be it a simple SoC unit or a more complex, uC controlled engine with various attached peripherals. From first prototype to the market, the following development cycle is typically walked through:


Favorite Tools: C++11 std::array

Matthew Eshleman February 26, 20172 comments

Many embedded software and firmware projects must be developed to high standards of reliability. To meet these reliability requirements, firmware project teams will consider many design tradeoffs. For example, an engineering team may avoid or outright ban the use of dynamic memory allocation, a feature typically accessed via the C library call "malloc" or the C++ allocator "new". When authoring software under such...


Important Programming Concepts (Even on Embedded Systems) Part III: Volatility

Jason Sachs October 10, 2014

1vol·a·tile adjective \ˈvä-lə-təl, especially British -ˌtī(-ə)l\ : likely to change in a very sudden or extreme way : having or showing extreme or sudden changes of emotion : likely to become dangerous or out of control

Merriam-Webster Online Dictionary

Other articles in this series:


Lessons Learned from Embedded Code Reviews (Including Some Surprises)

Jason Sachs August 16, 20152 comments

My software team recently finished a round of code reviews for some of our motor controller code. I learned a lot from the experience, most notably why you would want to have code reviews in the first place.

My background is originally from the medical device industry. In the United States, software in medical devices gets a lot of scrutiny from the Food and Drug Administration, and for good reason; it’s a place for complexity to hide latent bugs. (Can you say “


Bad Hash Functions and Other Stories: Trapped in a Cage of Irresponsibility and Garden Rakes

Jason Sachs January 28, 20141 comment

I was recently using the publish() function in MATLAB to develop some documentation, and I ran into a problem caused by a bad hash function.

In a resource-limited embedded system, you aren't likely to run into hash functions. They have three major applications: cryptography, data integrity, and data structures. In all these cases, hash functions are used to take some type of data, and deterministically boil it down to a fixed-size "fingerprint" or "hash" of the original data, such that...


Best Firmware Architecture Attributes

Dr. Tayyar GUZEL June 4, 20166 comments

Architecture of a firmware (FW) in a way defines the life-cycle of your product. Often companies start with a simple-version of a product as a response to the time-to-market caveat of the business, make some cash out of the product with a simple feature set. It takes only less than 2-3 years to reach a point where the company needs to develop multiple products derived from the same code base and multiple teams need to develop...


Cortex-M Exception Handling (Part 2)

Ivan Cibrario Bertolotti February 1, 20169 comments

The first part of this article described the conditions for an exception request to be accepted by a Cortex-M processor, mainly concerning the relationship of its priority with respect to the current execution priority. This part will describe instead what happens after an exception request is accepted and becomes active.

PROCESSOR OPERATION AND PRIVILEGE MODE

Before discussing in detail the sequence of actions that occurs within the processor after an exception request...


A wireless door monitor based on the BANO framework

Fabien Le Mentec June 10, 20145 comments
Introduction

I have been thinking for a while about a system to monitor the states of my flat and my garage doors from a remote place. Functionnaly, I wanted to monitor the state of my doors from a remote place. A typical situation is when I leave for holidays, but it can also be useful from the work office. To do so, I would centralize the information on a server connected on the Internet that I could query using a web browser. The server itself would be located in the appartement, where...


Donald Knuth Is the Root of All Premature Optimization

Jason Sachs April 17, 20172 comments

This article is about something profound that a brilliant young professor at Stanford wrote nearly 45 years ago, and now we’re all stuck with it.

TL;DR

The idea, basically, is that even though optimization of computer software to execute faster is a noble goal, with tangible benefits, this costs time and effort up front, and therefore the decision to do so should not be made on whims and intuition, but instead should be made after some kind of analysis to show that it has net...