Execute-Only Code with GNU and gcc

“There is no ‘S’ for Security in IoT” has indeed some truth. With all the connected devices around us, security of code should be a concern for every developer. “Preventing Reverse Engineering: Enabling Flash Security” shows how to prevent external read-out of critical code from device. What some microcontroller have built in is yet another feature: ‘Execute-Only-Sections‘ or ‘Execute-Only-Memory‘. What it means is that only instruction fetches are allowed in this area. No read access at all. Similar like ‘read-only’ ‘execute-only’ it means that code can be executed there, but no other access from that memory is allowed.

Locked Code

Locked Code

In this article I describe the challenges for a toolchain like the GNU gcc, and how to compile and link code for such an execute-only memory.

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Creating Disassembly Listings with GNU Tools and Eclipse

In many cases it is very useful to see the generated assembly code produced by the compiler. One obvious way to see the assembly code is to use the Disassembly view in Eclipse:

Disassembly View

Disassembly View

But this requires a debug session. An easier way is to use command line options to generate the listing file(s).

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Eclipse Debugging with Pointers and Arrays

In the C programming language it is good practice to pass values by reference (using a pointer), especially for large set of data. For example the following function takes a message string and pointer to integer data which then is printed to the console:

static void printData(const char *msg, const int *intBuf, size_t bufSize) {
  puts(msg); /* print message */
  for(int i=0; i<bufSize;i++) {
    printf("buf[%i] = %i\n", i, intBuf[i]);
  }
}

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McuOnEclipse Components: 1-July-2018 Release

’m pleased to announce that a new release of the McuOnEclipse components is available in SourceForge. This release includes several smaller bug fixes and initial component support for the NXP S32 Design Studio and SDK.

SourceForge

SourceForge

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Measuring ARM Cortex-M CPU Cycles Spent with the MCUXpresso Eclipse Registers View

The ARM DWT (Data Watchpoint and Trace) is an optional feature of the ARM-Cortex-M, and many Cortex-M3, M4 and M7 devices have it implemented. With it comes a cycle counter which counts the cycles spent. In Cycle Counting on ARM Cortex-M with DWT I described an approach how the application on the target can access the cycle counter.

The MCUXpresso IDE shows that cycle counter in the Eclipse Registers view:

Cycle Counter in Register View

Cycle Counter in Register View

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Installing Darkest Theme with MCUXpresso IDE 10.2

Is BLACK the color of the season? My students really seem to love these ‘dark’ Eclipse themes. Well, I tried ‘dark’ themes in the past, but I have not been vey excited about it. Somehow I preferred more the ‘black on white background’ thing. But: I have now managed to install the ‘Darkest Dark’ Eclipse theme into the NXP MCUXpresso 10.2 IDE for my daily work, and I feel it hurts my eyes less? Maybe I’m getting older? Or could it really be that ‘dark’ look and feel?

Darkest Dark Theme with MCUXpresso IDE

Darkest Dark Theme with MCUXpresso IDE

Find out for yourself in the following article….

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GNU Link Time Optimization finds non-matching Declarations

By default, the GNU compiler (gcc) optimizes each compilation unit (source file) separately. This is effective, but misses the opportunity to optimize across compilation units. Here is where the Link Time Optimization (LTO,  option -flto) can help out: with a global view it can optimize one step further.

The other positive side effect is that the linker can flag possible issues like the one below which are not visible to the compiler alone:

type of '__SP_INIT' does not match original declaration [enabled by default]
Warning by LTO

Warning by LTO

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Tutorial: Understanding and Using FreeRTOS Software Timers

Hardware Timers are essential to most embedded applications: I use them mostly for triggering actions at a given frequency, such as acquiring data from a  sensor. With using an RTOS I can do a similar thing using a task: the task will run with a given frequency and I can periodic work in it. However, using a task might be too much overhead doing this. The good news is that there is a much more efficient way to do this in FreeRTOS with Software Timers. And this is what this tutorial is about: how to use Software Timers with FreeRTOS.

FreeRTOS Software Timers

FreeRTOS Software Timers

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Understanding FreeRTOS Task Stack Usage and Kernel Awareness Information

When using the FreeRTOS Task List in the Eclipse based MCUXpresso IDE, it shows the list of tasks with their stack size used. But with the default FreeRTOS settings it is not able to determine the correct stack size and shows a warning icon:

Warning for Stack Usage

Warning for Stack Usage

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Overview of MCUXpresso IDE v10.2.0

Decisions, decisions! Such long weekends like Pentecost are a real challenge for a family with engineers:

  1. Should we join that record long traffic jam to Italy and be stuck for more than 4 hours and analyze it?
  2. Or: should we stay home, turn the BBQ smoker engine on fire, load it with baby back pork rib racks for a slow-and-low smoke treatment, while doing some on-the-side IDE and technology exploration?

Well, my family vote was kind of clear: they have chosen that second option. Not to mention that hidden technology piece in it, but that was part of the deal ;-).

And I’m sorry: this article is not about BBQ (for this see “Smoking BBQ Baby Back Ribs – Swiss Style“), it is about technology: I’m using the NXP MCUXpresso IDE and tools for many of my projects (see “Eclipse MCUXpresso IDE 10.1 with integrated MCUXpresso Configuration Tools“). Right before the this extended weekend, NXP has released the new v10.2.0 version, so here is where that technology exploration piece comes into play. Checking the release notes, this version number change includes so many cool stuff I decided to have a look and to check it out. Of course always having an electronic eye on the baby back ribs!

MCUXpresso IDE v10.2.0

MCUXpresso IDE v10.2.0

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Debugging ARM Cores with IP based Debug Probes and Eclipse

Using IP (Ethernet) based debug probes is a very handy thing: I don’t have to be directly connected to the debug probe (e.g. with the USB cable). This article explains how to use an IP-based Segger or P&E probe with the Eclipse based MCUXpresso IDE.

LAN Based Debugging

LAN Based Debugging

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Listing Code and Data Size with GNU nm in Eclipse

The map file produced by the GNU linker includes lots of information, however it is very cryptic to read. In “Listing Code and Data Size for each Source File with GNU and Eclipse” I showed how the GNU size utility can be used to report the code and data size for each object file. The Eclipse based MCUXpresso IDE comes with another nice view which shows detailed information about code and data allocation:

Symbol Viewer in MCUXpresso IDE

Symbol Viewer in MCUXpresso IDE

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McuOnEclipse Components: 1-Apr-2018 Release

It’s April Fool’s Day, but be assured this is not a joke ;-): I’m pleased to announce that a new release of the McuOnEclipse components is available in SourceForge. This release includes several smaller bug fixes and components have been upgraded for FreeRTOS V10.0.1.

SourceForge

SourceForge

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Flash-Resident USB-HID Bootloader with the NXP Kinetis K22 Microcontroller

The tinyK22 board (see “tinyK22 Boards arrived“) gets rolled out at the Lucerne University of Applied Sciences and Arts, so I thought I write-up an article this weekend how to use that board with a Flash Resident Bootloader.

tinyK22 with USB HID Bootloader

tinyK22 with USB HID Bootloader

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Performance and Runtime Analysis with FreeRTOS

One of the great things with the FreeRTOS operating system is that it comes with free performance analysis: It shows me how much time is spent in each task. Best of all: it shows it in a graphical way inside Eclipse too:

FreeRTOS Runtime Information in Eclipse

FreeRTOS Runtime Information in Eclipse

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Debugging the Teensy 3.6 with Eclipse MCUXpresso IDE and CMSIS-DAP LPC-Link2

The Teensy boards are great, but as they are they are not really useful for real development, as they lack proper SWD debugging. In “Modifying the Teensy 3.5 and 3.6 for ARM SWD Debugging” I have found a way to get SWD debugging working, at that time with Kinetis Design Studio and the Segger J-Link. This article is about how debug the Teensy with free MCUXpresso IDE and the $20 NXP LPC-Link2 debug probe:

Teensy 3.6 with NXP LPC-Link2

Teensy 3.6 with NXP LPC-Link2

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MCUXpresso IDE V10.1.0 with i.MX RT1052 Crossover Processor

In “Eclipse MCUXpresso IDE 10.1 with integrated MCUXpresso Configuration Tools” I mentioned that I wanted to try the i.MX RT1050 processor. Well, finally my ordered board from Mouser arrived, right on time for the week-end, so I had a chance to use that ARM Cortex-M7 running at 600 MHz :-).

i.MX RT1050 EVK

i.MX RT1050 EVK

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New FreeRTOS V10.0.0: Amazon, Segger SystemView and Percepio Tracealyzer

“Amazon FreeRTOS – IoT operating system for microcontrollers”: The announcement of FreeRTOS V10.0.0 was one of the biggest news last week for me. Not only is there now a Version 10, the bigger news is that FreeRTOS is now part of Amazon. Wow! Now this explains why Richard Barry (the founder behind FreeRTOS) was kind of hiding away for about a year: he joined Amazon as a principal engineer about a year ago. I think we all have to wait and see what it means for FreeRTOS.

Amazon FreeRTOS

Amazon FreeRTOS (Source: Amazon Web Site)

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