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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.


Trust, but Verify: Examining the Output of an Embedded Compiler

Jason Sachs September 27, 2015

I work with motor control firmware on the Microchip dsPIC33 series of microcontrollers. The vast majority of that firmware is written in C, with only a few percent in assembly. And I got to thinking recently: I programmed in C and C++ on an Intel PC from roughly 1991 to 2009. But I don’t remember ever working with x86 assembly code. Not once. Not even reading it. Which seems odd. I do that all the time with embedded firmware. And I think you should too. Before I say why, here are...


Improving the Reload2 active load

Fabien Le Mentec April 23, 2015
Introduction

With another colleague at work, we are currently developing an electronic board that will eventually be powered over Ethernet. To gain more experience with this technology, we prototyped a standalone power supply stage.

We want to test this stage with different load profiles. While we already have professional grade active loads at work, I had previously read about the Reload2 product from Arachnidlabs, a low cost active load sold on Hackaday:


Slew Rate Limiters: Nonlinear and Proud of It!

Jason Sachs October 6, 2014

I first learned about slew rate limits when I was in college. Usually the subject comes up when talking about the nonideal behavior of op-amps. In order for the op-amp output to swing up and down quickly, it has to charge up an internal capacitor with a transistor circuit that’s limited in its current capability. So the slew rate limit \( \frac{dV}{dt} = \frac{I_{\rm max}}{C} \). And as long as the amplitude and frequency aren’t too high, you won’t notice it. But try to...


Introduction to Microcontrollers - 7-segment displays & Multiplexing

Mike Silva August 14, 20141 comment

Doing the 7 Segment Shuffle

The 7 segment display is ubiquitous in the modern world.  Just about every digital clock, calculator and movie bomb has one.  The treadmills at my gym have 6 or 7, each one displaying 3 or 4 digits.  What makes the 7-seg interesting is that it presents an opportunity to make a trade off between GPIO (output pins) for time.  Every 7-seg display requires 8 outputs (the 7 segments and usually either a decimal point or a...


OOKLONE: a cheap RF 433.92MHz OOK frame cloner

Fabien Le Mentec August 12, 201417 comments
Introduction

A few weeks ago, I bought a set of cheap wireless outlets and reimplemented the protocol for further inclusion in a domotics platform. I wrote a post about it here:

//www.embeddedrelated.com/showarticle/620.php

Following that, I had access to another outlet from a different vendor:

http://www.castorama.fr/store/Prise-telecommandee-BLYSS---Interieur-prod4470027.html

The device documentation mentions that it operates on the same frequency as the previous...


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,...


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...


Using a RTLSDR dongle to validate NRF905 configuration

Fabien Le Mentec January 27, 20146 comments
I am currently working on a system to monitor the garage door status from my flat. Both places are 7 floors apart, and I need to send the data wirelessly. I chose to operate on the 433MHz carrier, and I ordered 2 PTR8000 modules: http://www.electrodragon.com/w/NRF905_Transceiver_433MHz-Wireless_ModuleThe PTR8000 is based on the dual band sub 1GHz NRF905 chipset from NORDICSEMI: http://www.nordicsemi.com/eng/Products/Sub-1-GHz-RF/nRF905I...

How to Arduino - a video toolbox

Lonnie Honeycutt November 15, 20131 comment

I've begun producing a new series of video tutorials for the hobbyist new to the Arduino or microcontrollers in general.  My videos are very pragmatic - I prefer to answer the question "what is the quickest, simplest and most affordable way to accomplish this?".  The videos are meant to be a quick source of "how to" knowledge for the hobbyist that is using an LCD display, ultrasonic sensor or accelerometer for the first time, for example.  I hope you enjoy this series of...


Are We Shooting Ourselves in the Foot with Stack Overflow?

Miro Samek September 8, 20234 comments

Most traditional, beaten-path memory layouts allocate the stack space above the data sections in RAM, even though the stack grows “down” (towards the lower memory addresses) in most embedded processors. This arrangement puts your program data in the path of destruction of a stack overflow. In other words, you violate the first Gun Safety Rule (ALWAYS keep the gun pointed in a safe direction!) and you end up shooting yourself in the foot. This article shows how to locate the stack at the BEGINNING of RAM and thus point it in the "safe" direction.


Getting Started With Zephyr: Devicetree Overlays

Mohammed Billoo September 25, 2023

In this blog post, I show how the Devicetree overlay is a valuable construct in The Zephyr Project RTOS. Overlays allow embedded software engineers to override the default pin configuration specified in Zephyr for a particular board. In this blog post, I use I2C as an example. Specifically, I showed the default I2C pins used for the nRF52840 development kit in the nominal Zephyr Devicetree. Then, I demonstrated how an overlay can be used to override this pin configuration and the final result.


Improving the Reload2 active load

Fabien Le Mentec April 23, 2015
Introduction

With another colleague at work, we are currently developing an electronic board that will eventually be powered over Ethernet. To gain more experience with this technology, we prototyped a standalone power supply stage.

We want to test this stage with different load profiles. While we already have professional grade active loads at work, I had previously read about the Reload2 product from Arachnidlabs, a low cost active load sold on Hackaday:


NULL pointer protection with ARM Cortex-M MPU

Miro Samek July 16, 2023

This post explains how you can set up the ARM Cortex-M MPU (Memory Protection Unit) to protect thy code from dragons, demons, core dumps, and numberless other foul creatures awaiting thee after thou dereference the NULL pointer.


Getting Started With Zephyr: Kconfig

Mohammed Billoo June 22, 2023

In this blog post, we briefly look at Kconfig, one of the core pieces of the Zephyr infrastructure. Kconfig allows embedded software developers to turn specific subsystems on or off within Zephyr efficiently and control their behavior. We also learn how we can practically use Kconfig to control the features of our application using the two most common mechanisms.


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...


Embedded Systems - free EdX course by UT-Austin!

Lonnie Honeycutt October 29, 20131 comment

I was very excited to see that there will be an Embedded Systems class available for free at https://www.edx.org/course/utaustin/ut-6-01x/embedded-systems-shape-world/1172

It's free to sign up and take the online class at the EdX website.

More exciting is that the class is based on a TI Launchpad Tiva microcontroller development board.  The Tiva Launchpad features an 80-MHz ARM Cortex M-4 MCU with 256 KB of flash storage, 32 KB of RAM and 43 general purpose I/O pins.  


Introduction to Deep Insight Analysis for RTOS Based Applications

Jacob Beningo September 20, 20171 comment

Over the past several years, embedded systems have become extremely complex. As systems become more complex, they become harder and more time consuming to debug. It isn’t uncommon for development teams to spend more than 40% development cycle time just debugging their systems. This is where deep insight analysis has the potential to dramatically decrease costs and time to market.

Defining Deep Insight Analysis

Deep insight analysis is a set of tools and techniques that can be...


Write Better Code with Block Diagrams and Flowcharts

Nathan Jones August 1, 20241 comment

Reading and writing code without architectural diagrams is like trying to follow complex instructions without any explanatory pictures: nigh impossible! By taking the time to draw out the block diagrams and flowcharts for your code, you can help identify problems before they arise and make your code easier to design, write, test, and debug. In this article, I'll briefly justify the importance of architectural drawings such as block diagrams and flowcharts and then teach you what they are and how to draw them. Using two simple examples, you'll see first-hand how these drawings can significantly amplify your understanding of a piece of code. Additionally, I'll give you a few tips for how to implement each drawing once you've completed it and I'll share with you a few neat tools to help you complete your next set of drawings.


Getting Started With Zephyr: Writing Data to EEPROM

Mohammed Billoo December 6, 20235 comments

In this blog post, I show how to implement a Zephyr application to interact with EEPROM. I show how the Zephyr device driver model allows application writers to be free of the underlying implementation details. Unfortunately, the application didn't work as expected, and I'm still troubleshooting the cause.