Using the C language to program the am335x PRU
Introduction
Some weeks ago, I published an article on how we used the PRU to implement a power supply control loop having hard realtime constraints:
//www.embeddedrelated.com/showarticle/586.php
Writing this kind of logic in assembly language is not easy. First the assembly language itself may be difficult to learn depending on your background. Then, fixed and floating point arithmetics require lot of code. While macros help to handle the complexity, they still are error prone as you...
How to make a heap profiler
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...
Using the Beaglebone PRU to achieve realtime at low cost
IntroductionI work as an engineer in a synchrotron facility. A few weeks ago, I helped the people in charge of the power supply developments to integrate a realtime control algorithm on a prototype platform: a BeagleBone Black (BBB) running Linux. I had already worked with this board in the past, and I found it very interesting given its excellent resources versus price ratio (around 40 euros). This time, I was impressed by its realtime capabilities. I thought it would be a good idea to...
Unit Tests for Embedded Code
I originate from an electrical engineering background and my first industry experience was in a large, staid defense contractor. Both of these experiences contributed to a significant lack of knowledge with regards to software development best practices. Electrical engineers often have a backwards view of software in general; large defense contractors have similar views of software and couple it with a general disdain for any sort of automation or ‘immature’ practices. While there...
Bad Hash Functions and Other Stories: Trapped in a Cage of Irresponsibility and Garden Rakes
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...
Implementing State Machines
State machines are a great way to design software but they can be difficult to implement well.To illustrate this I’ll develop a simple state machine then increase the complexity to demonstrate some of the difficulties
We’ve all washed dishes before - it’s easy isn’t it? Scrub, rinse, dry, scrub, rinse dry. Scrub the dish until all of the gunk is off of it, rinse until the soap is off, put it in the drying rack. If you want to design software to implement this you have options. You...
Understanding and Preventing Overflow (I Had Too Much to Add Last Night)
Happy Thanksgiving! Maybe the memory of eating too much turkey is fresh in your mind. If so, this would be a good time to talk about overflow.
In the world of floating-point arithmetic, overflow is possible but not particularly common. You can get it when numbers become too large; IEEE double-precision floating-point numbers support a range of just under 21024, and if you go beyond that you have problems:
for k in [10, 100, 1000, 1020, 1023, 1023.9, 1023.9999, 1024]: try: ...Delayed printf for real-time logging
You often debug by adding a few printfs and looking at the logs. In some real-time/low-level contexts though, you don't have time for text formatting.
You don't want prints to affect timing too much, because then timing-related bugs you're chasing might disappear. And you certainly don't want the system to stop functioning altogether because prints cause it to miss real-time deadlines.
A common alternative to prints is more "raw" logging - an event buffer, where event is a union keeping...
Coroutines in one page of C
A coroutine is a function that you can jump back into after returning from it - and it remembers where it was in the code, and all the variables. This is very useful at times.
One use is generating a sequence of values. Here's how you can generate all the x,y pairs in a 2D range in Python:
def iterate(max_x, max_y): for x in range(max_x): for y in range(max_y): yield x,y for x,y in iterate(2,2): print x,yThis prints:
0 0 0 1 1 0 1 1The yield keyword is like...
Code Metrics - SLOC Count
Many programmers will start having flashbacks at the title of this article because it contains the words 'metrics' and 'SLOC'. Newer programmers are probably wondering what all of the fuss is about - most probably have no negative connotations with the term 'code metrics' and some may not even know what SLOC is. While there is much baggage associated with metrics and SLOC you shouldn't be afraid to gather fundamentally useful data such as SLOC count from your programming projects...
Modern Embedded Systems Programming: Beyond the RTOS
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...
How to make a heap profiler
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...
Tenderfoot: Introduction to Magic (Numbers that is...)
Once upon a time, while participating in a source code review, I stumbled across the following C code in a header file:
struct Foo { //various structure fields char string_buffer[45+3]; //buffer requires about 45 bytes };My right eyebrow raised, I took a note, and continued with the code review, only to later stumble into this line of code in the body of a C function:
char * temp_string_buffer = (char*) malloc(45+3);Again, I took a note on this function, and continued...
Designing Embedded System with FPGA - 1
With the introduction of soft processors and related tools (like EDK from Xilinx), implementation of basic embedded system in FPGA is made easy. This requires very little or almost no knowledge of VHDL programming. Actually that’s how I started. If user is interested in taking full advantage of FPGA and its parallel processing power, then yes, detail understanding of soft processor, its peripheral bus and VHDL programming is required.
I will start with...
Embedded Firmware Refactoring, Optimisation and Migration
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...
Developing software for a safety-related embedded system for the first time
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.
...Cutting Through the Confusion with ARM Cortex-M Interrupt Priorities
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...
Coding Step 4 - Design
Articles in this series:
- Coding Step 0 - Development Environments
- Coding Step 1 - Hello World and Makefiles
- Coding Step 2 - Source Control
- Coding Step 3 - High-Level Requirements
- Coding Step 4 - Design
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....
Vala applications on Embedded Linux: maybe a clever choice [part 1]
Vala is a sexy, open source, high level programming language that appeared in 2006, it counts with a modern typing system, is object oriented, compiled and statically typed, it has a almost identical syntax to C# and is maintained by GNOME. The language was created as a power abstraction of the GLib and GTK libraries, two considerably lightweight and powerful libraries written in C, and it is used in projects such as GNOME Clocks, Shotwell, GXml and Elementary OS.
namespace...Favorite Tools - Look Up Tables
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 tablesLook 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...
Modulation Alternatives for the Software Engineer
Before I get to talking about modulation, here's a brief diversion.
A long time ago -- 1993, to be precise -- I took my first course on digital electronics and processors. In that class, we had to buy a copy of the TTL Data Book* from Texas Instruments.
If you have any experience in digital logic design you probably know that TTL stands for Transistor-transistor logic (thereby making the phrase "TTL Logic" an example of RAS...
Coding Step 4 - Design
Articles in this series:
- Coding Step 0 - Development Environments
- Coding Step 1 - Hello World and Makefiles
- Coding Step 2 - Source Control
- Coding Step 3 - High-Level Requirements
- Coding Step 4 - Design
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....
Deeply embedded design example - Logic replacement
I have always believed that some of the low-cost, low-pin count, low-resource microprocessors would make an excellent choice for the replacement of discrete logic components. In these cases the deeply embedded microprocessor would become less of a general purpose computer and more of a logic replacement, providing a prescribed function with no connection to the outside world. In a world of bigger, faster and more expensive, it is a pleasant change of pace...
Tenderfoot: Recommended Reading
Twenty years ago I read Code Complete by Steve McConnell. And then read it again. And again. And again. Of all the books I have read during my career, I believe this was the book that catapulted me from a young electrical engineer to a young and aspiring embedded software engineer. So to all the ‘tenderfoots’ embarking upon an embedded systems and especially embedded software and firmware career, this entry is for you.
First, I would certainly recommend that all engineers read and read...
Embedded Toolbox: Windows GUI Prototyping Toolkit
In this installment of my "Embedded Toolbox" series, I would like to interest you in the free Windows GUI Toolkit called QWin for prototyping, developing and debugging embedded C or C++ code on Windows.
If you work on devices with non-trivial user interfaces consisting of LCDs (segmented or graphic), buttons, LEDs, etc., QWin could be just the tool for you. It has improved my productivity in such projects dramatically. I personally consider it a gem in my "Embedded...
C++ on microcontrollers 3 – a first shot at an hc595 class with 8 output pins
This blog series is about the use of C++ for modern microcontrollers. My plan is to show the gradual development of a basic I/O library. I will introduce the object-oriented C++ features that are used step by step, to provide a gentle yet practical introduction into C++ for C programmers. Reader input is very much appreciated, you might even steer me in the direction you find most interesting.
In the first part of...
Introduction to Deep Insight Analysis for RTOS Based Applications
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...
Surprising Linux Real Time Scheduler Behavior
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...
Embedded Programming Video Course Teaches RTOS
If you'd like to understand how a Real-Time Operating System (RTOS) really works, here is a free video course for you:
RTOS part-1: In this first lesson on RTOS you will see how to extend the foreground/background architecture from the previous lesson, so that you can have multiple background loops running seemingly simultaneously.:
RTOS part-2: In this second lesson on RTOS you will see how to automate the context switch process. Specifically, in this lesson, you will start building...
Vala applications on Embedded Linux: maybe a clever choice [part 1]
Vala is a sexy, open source, high level programming language that appeared in 2006, it counts with a modern typing system, is object oriented, compiled and statically typed, it has a almost identical syntax to C# and is maintained by GNOME. The language was created as a power abstraction of the GLib and GTK libraries, two considerably lightweight and powerful libraries written in C, and it is used in projects such as GNOME Clocks, Shotwell, GXml and Elementary OS.
namespace...
