#Sample code

[wordacrosstime]

Programming Embedded Systems (with C and GNU Development Tools)

[Programming Embedded Systems (with C and GNU Development Tools). By Michael Barr & Anthony J Massa. 2nd Edition, 1 October 2006. Publisher: O'Reilly Media. Paperback: 301 pages, Dimensions: ‎ 17.78 x 1.98 x 23.34 cm. ISBN: 978-0-596-00983-0]

In the past 15 months or so I elected to expand my personal and professional skill set to include working with small computing systems, sometimes referred to as microcontrollers.  These devices have become virtually omnipresent, in everything from automobiles and bar-code scanners to toasters and doorbells.  If you operate a late-model vehicle, for instance, you may have as many as 70 (!) of these devices in the car controlling everything from the fuel mixture to emissions to anti-lock brakes and collision avoidance sensing.

I was interested in moving into this arena as part of my career, as there were many openings for people with a strong understanding of the imperatives attendant on both the software and hardware of embedded systems.  I knew a bit about the electronics side of things and I have done software development of one sort or another most of my 40+ years as a professional, but this arena poses unique challenges and opportunities.  I knew I needed to do some specialized self-teaching, and this book seemed like a great place to start.

To start with, what exactly is an embedded system?

As the name implies, it is a system - in this case a miniature computing device - that is a component of a larger framework.  This larger framework can take on myriad forms.  Some of the largest such frameworks are satellite networks.  The embedded system comprises hardware - a central processing unit, or CPU, along with some (minimal) on-board memory and one or more electrical interfaces (e.g. a USB or RJ45 jack) through which it can communicate with the outside world. 

Unlike the computers most of us are familiar with, such as Windows or MacOS-based laptops or Linux servers, these devices often do not have an operating system (WIndows, MacOS and Linux are all operating systems) that performs many of the low-level functions needed to keep the device running and useful. 

This keeps the device flexible in terms of how it can be used, but at the expense of more detailed and subtle development and maintenance requirements.  Thus, the "software" on an embedded system may be a very small bit of computer code that simply turns on the interfaces electrically and then waits for something to happen.

Programming software for these systems is intriguing but fraught with issues that an ordinary computer user never sees.

For example, given that the memory and interface resources on these devices tend to be rather modest, it's necessary for the programmer to take care of any bookkeeping that is necessary to keep the basic functions from colliding.  If one of the interfaces is used to provide a scanned barcode to a waiting receiver, it must pass that information through some on-board memory first.

The embedded software designer needs to be sure that this information can't be corrupted, or "clobbered", by a competing task that might be, for instance, putting the scanning laser into sleep mode to save power.  Moreover, there are cases where the same locations in memory need to be shared by tasks as a part of getting work done.

But what happens if one task is trying to write data to a specific memory location while another task is trying to read from it?  Is there always a specific order in which this happens?  What happens if either operation is incomplete for some reason?  Will the device recover and continue to operate, or will it lock up?  The aforementioned are but a tiny set of examples that the developer must bear in mind.

Messrs Barr and Massa have many decades of experience between the two of them in just these kinds of environments. I was delighted to see just how easy this book is to read and how thoroughly they cover all of the issues that accompany such a software development enterprise.  They are careful to create and explain examples that use commonly-available development kits (I use an STM32 ARM Cortex-M Development Board myself; there is a photo of one such system below) and free or nearly-free software tools to break down the barriers to entry in this field.

This book is really as much about operating system design as it is about microcontroller software development; if one is interested in what nearly every operating system must do, this volume talks all about it. 

Above and beyond this, it is a wealth of anecdotes, sample code, and general wisdom that will really ease the novice into this exciting world of programming and small-device control.

I highly recommend it to anyone who wants to get down on the bare metal with computers.  It is necessary to be at least familiar with the C programming language (almost all of the examples are coded in C) and it would be very helpful to have worked with at least one Assembly language as well.  Beyond that, the only requirement for getting the most out of the book is a willingness to experiment and be delighted.

Image Credits (from above down; with thanks to copyright owners): (1) STM32 ARM Cortex-M Development Board © Copyright Owner, date unknown (2) Book Cover © O'Reilly Media 11 October 2006 (3) Michael Barr © Barr Group 2012-2025. (Anthony J Massa, no photograph found)

Kevin Gillette

Words Across Time

4 February 2025

wordsacrosstime

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