Tag Archives: C Programming

‘Abusing’ the C switch statement – beauty is in the eye of the beholder

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

The C Language

Before we start, let’s get something straight; for over 30 years now I have had a love-hate relationship with the C programming language. The ‘engineer’ in me[1] sometimes just cannot believe we are still using C as the dominant embedded programming languages after all these years, and yet, I also see the simplicity and elegance the C code can bring. After all it’s just a tool, and even a good tool in the wrong hands; well we have plenty […]

Posted in C/C++ Programming | Tagged , , | 28 Comments

Function Parameters and Arguments on 32-bit ARM

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

Function call basics

When teaching classes about embedded C  or embedded C++ programming, one of the topics we always address is “Where does the memory come from for function arguments?“

Take the following simple C function:

void test_function(int a, int b, int c, int d);

when we invoke the function, where are the function arguments stored?

int main(void)
{
  //…
  test_function(1,2,3,4);
  //…
}

Unsurprisingly, the most common answer after “I don’t know” is “the stack“; and of course if you were compiling for x86 this would […]

Posted in ARM, C/C++ Programming, Cortex | Tagged , , | 5 Comments

goto fail and embedded C Compilers

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

I can’t imagine anyone reading this posting hasn’t already read about the Apple “goto fail” bug in SSL. My reaction was one of incredulity; I really couldn’t believe this code could have got into the wild on so many levels.

First we’ve got to consider the testing (or lack thereof) for this codebase. The side effect of the bug was that all SSL certificates passed, even malformed ones. This implies positive testing (i.e. we can demonstrate it works), but no negative testing […]

Posted in ARM, C/C++ Programming, Industry Analysis, Testing | Tagged , , , , , | 5 Comments

Shock horror! I learned something about arrays in C

Glennan Carnie

Glennan Carnie

Technical Consultant at Feabhas Ltd
Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.
Glennan Carnie

Latest posts by Glennan Carnie (see all)

Every so often you pick up a snippet of information that completely changes the way you view things. This week, it’s the use of arrays as function parameters.

At first glance the code horrified me (as I’m sure it will horrify some of you out there!) but as I’ve played with it I can see real merit in the technique.

Arrays, pointers and syntactic sugar

In C there is a close (if somewhat messy!) relationship between arrays and pointers. As far as the […]

Posted in C/C++ Programming | Tagged , , , , | 12 Comments

Developing a Generic Hard Fault handler for ARM Cortex-M3/Cortex-M4

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

This posting assumes you that you have a working ARM Cortex-M3 base project in Keil uVision. If not, please see the “howto” video: Creating ARM Cortex-M3 CMSIS Base Project in uVision

Divide by zero error

Given the following C function

int div(int lho, int rho)
{
return lho/rho;
}

called from main with these arguments

int main(void)
{
int a = 10;
int b = 0;
int c;
c = div(a, b);
// other code
}

You […]

Posted in ARM, C/C++ Programming, CMSIS, Cortex | Tagged , , , | 16 Comments

IoT – MQTT Publish and Subscriber C Code

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

With the buzz around the Internet-of-Things (IoT), I felt I needed to get in on the act. For those that follow my twitter feed (@feabhas) you may be aware of the “home project” I’ve been working on. This project is based around the mbed platform to which I have connected a DS18B20 temperature sensor. The overall goal is to record the water temperature of my son’s fish tank, however due to water quality issues, it is currently sampling the air […]

Posted in C/C++ Programming | Tagged , , , | 3 Comments