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, 201516 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 4 - Design

Stephen Friederichs November 24, 2015

Articles in this series:

The last article in this series discussed how to write functional high-level requirements: specifications for what your software is supposed to do. Software design is the other side of the coin....


The three laws of safe embedded systems

Michael J. Pont November 12, 20151 comment

This short article is part of an ongoing series in which I aim to explore some techniques that may be useful for developers and organisations that are beginning their first safety-related embedded project.

In the last two weeks, I’ve had the opportunity to discuss the contents of my previous article on this site with a group of very smart and enthusiastic engineers in Cairo (Egypt). As part of this discussion, it has become clear that I should add a few more details to explain the work...


Developing software for a safety-related embedded system for the first time

Michael J. Pont October 31, 20151 comment

I spend most of my working life with organisations that develop software for high-reliability, real-time embedded systems. Some of these systems are created in compliance with IEC 61508, ISO 26262, DO-178C or similar international standards.

When working with organisations that are developing software for their first safety-related design, I’m often asked to identify the key issues that distinguish this process from the techniques used to develop “ordinary” embedded software.

...

“Smarter” cars, unintended acceleration – and unintended consequences

Michael J. Pont October 20, 20151 comment

In this article, I consider some recent press reports relating to embedded software in the automotive sector.

In The Times newspaper (London, 2015-10-16) the imminent arrival of Tesla cars that “use autopilot technology to park themselves and change lane without intervention from the driver” was noted.

By most definitions, the Tesla design incorporates what is sometimes called “Artificial Intelligence” (AI).Others might label it a “Smart” (or at least “Smarter”)...


Coding Step 3 - High-Level Requirements

Stephen Friederichs August 17, 20152 comments

Articles in this series:

If this series of articles has been light on one thing it's 'coding'. If it's been light on two things the second is 'embedded'. In three articles I haven't gotten past Hello World on a desktop PC. That changes (slowly) with this article. In this article I'll...


Lessons Learned from Embedded Code Reviews (Including Some Surprises)

Jason Sachs August 16, 20151 comment

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 “


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:


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:


Lazy Properties in Python Using Descriptors

Jason Sachs November 7, 2017

This is a bit of a side tangent from my normal at-least-vaguely-embedded-related articles, but I wanted to share a moment of enlightenment I had recently about descriptors in Python. The easiest way to explain a descriptor is a way to outsource attribute lookup and modification.

Python has a bunch of “magic” methods that are hooks into various object-oriented mechanisms that let you do all sorts of ridiculously clever things. Whether or not they’re a good idea is another...


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...


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...


Interfacing LINUX with microcontrollers

Fabien Le Mentec May 7, 20132 comments
Introduction

I am increasingly asked to work on small spare time projects where a user needs to control some device over the INTERNET. Recently, a friend needed to control heater relays and measure the temperature of its geographically distant secondary house. Another case relates to the control of a pan tilt home monitoring camera. A last one is the control of an old XY plotter DACs.

In both applications, the user wants to access the system over a web browser using HTTP. From the user...


How to make a heap profiler

Yossi Kreinin May 23, 2014

We'll see how to make a heap profiler. Example code for this post makes up heapprof, a working 250-line heap profiler for programs using malloc/free.

It works out of the box on Linux (tested on "real" programs like gdb and python). The main point though is being easy to port and modify to suit your needs. The code, build and test scripts are at github.

Why roll your own heap profiler?

  • It's easy! And fun, if you're that sort of person. What, not reasons enough? OK, how...

Introduction to Microcontrollers - Ada - 7 Segments and Catching Errors

Mike Silva September 22, 20145 comments

7 Segments the Ada Way

Here is the Ada version (I should say AN Ada version) of the 7 segment multiplexing code presented in the last installment.  The hardware now is the STM32F407 Discover board, which is a Cortex M4F board.  There are lots of differences in GPIO and timer setup, but if you understoold the previous code in C you should not have much trouble understanding this code in Ada.

As interesting as the Ada approach to the task is the Ada ability to detect...


Reverse engineering wireless wall outlets

Fabien Le Mentec July 19, 2014
Introduction

I am improving the domotics framework that I described in a previous article://www.embeddedrelated.com/showarticle/605.php

I want to support wireless wall outlets, allowing me to switch devices power from a remote location over HTTP.

To do so, I could design my own wireless wall outlets and use a hardware similar to the previous one, based on the NRF905 chipset. The problem is that such a product would not be certified, and that would be an issue regarding the home insurance,...


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...