Programming the ESP32 with an ARM Cortex-M USB CDC Gateway

The Espressif ESP32 devices are getting everywhere: they are inexpensive, readily available and Espressif IDF environment and build system actually is pretty good and working well for me including Eclipse (see “Building and Flashing ESP32 Applications with Eclipse“). The default way to program an ESP32 is to a) enter UART bootloader by pressing some push buttons and b) flash the application with ESP-IDF using a USB cable.

That works fine if the ESP32 is directly connected to the host PC. But in my case it is is behind an NXP Kinetis K22FX512 ARM Cortex-M4F microcontroller and not directly accessible by the host PC. So I had to find a way how to allow boot loading the ESP32 through the ARM Cortex-M which is the topic of this article.

TTGO ESP32 MICRO-D4 Module

TTGO ESP32 MICRO-D4 Module

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Building a Raspberry Pi UPS and Serial Login Console with tinyK22 (NXP K22FN512)

There are different ways to ruin a Linux system. For the Raspberry Pi which uses a micro SD card as the storage device by default, it comes with two challenges:

  1. Excessive writes to the SD card can wear it out
  2. Sudden power failure during a SD card write can corrupt the file system

For problem one I do I have a mitigation strategy (see “Log2Ram: Extending SD Card Lifetime for Raspberry Pi LoRaWAN Gateway“). Problem two can occur by user error (“you shall not turn it off without a sudo poweroff!”) or with the event of a power outage or black out. So for that problem I wanted to build a UPS for the Raspberry Pi.

Raspberry Pi with UPS System and tinyK22

Raspberry Pi with UPS System and tinyK22

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Be aware: Floating Point Operations on ARM Cortex-M4F

My mantra is *not* to use any floating point data types in embedded applications, or at least to avoid them whenever possible: for most applications they are not necessary and can be replaced by fixed point operations. Not only floating point operations have numerical problems, they can lead to performance problems as in the following (simplified) example:

#define NOF  64
static uint32_t samples[NOF];
static float Fsamples[NOF];
float fZeroCurrent = 8.0;

static void ProcessSamples(void) {
  int i;

  for (i=0; i < NOF; i++) {
    Fsamples[i] = samples[i]*3.3/4096.0 - fZeroCurrent;
  }
}

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Tutorial: HD44780 Display Driver with NXP MCUXpresso SDK

In the age of high-resolution graphical LCDs using a character display might look like a bit anachronistic. But these displays provide a lot of value for me as they are robust, available in different shapes and number of lines. And such a character display can be a better solution for an industrial application.

hd44780 display with NXP FRDM-KW41Z Board

hd44780 display with NXP FRDM-KW41Z Board

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FreeRTOS: how to End and Restart the Scheduler

Most host or desktop systems (say Linux, Mac or Windows) have a normal use case where you start the operating system say in the morning and shut it down in the evening, and then you leave the machine. Embedded Systems are different: they are not attended, and they are supposed to run ‘forever’. Not every embedded system needs to run an OS (or in that world: Real-Time Operating System or RTOS), but the same applies here: after the RTOS is started, it is not intended that it will shutdown and restart. To the extend that you won’t they support the ‘shutdown’ and ‘restart’ functionality at all. In case of gathering coverage information this would be really useful:

coverage information from freertos application

coverage information from FreeRTOS application

In the case of FreeRTOS: what if I really need to shutdown the RTOS and restart it again, as by default this is not supported. This is what this article is about …

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GDB All-Stop and Non-Stop Mode with LinkServer

GDB supports a mode which allows the GDB debug client to read memory while the target is running. This allows features like ‘live variables’: that way I can see the variables refreshed and changing over time without halting the target. Another functionality which comes with that feature is to check stopped threads or to see all threads in the system.

multiple freertos threads in debug view

multiple FreeRTOS threads in debug view

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Driver for VL53L0X Time-Of-Flight (ToF) Sensor and NXP K20DX128

I’m using the VL6180X ToF (Time-of-Flight) sensors successfully in different projects. The VL6180X is great, but only can measure distances up to 20 cm and in ‘extended mode’ up to 60 cm. For a project I need to go beyond that, so the logical choice is the VL53L0X which measures between 30 cm and 100 cm or up to 200 cm. For this project I’m using the VL53L0X breakout board from Adafruit, but similar products are available e.g. from Pololu.

NXP K20dx128 with adafruit vl53l0x tof sensor

NXP K20dx128 with Adafruit VL53LOx tof sensor

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Playing Zork with FreeRTOS on ARM in three different Ways

You might wonder what ‘Zork‘ is? Zork is one of the first and earlist fictive computer games, written around 1977 and 1979, written in MDL on a DEC PDP-10 by members of the MIT Dynamic Modelling group (see https://en.wikipedia.org/wiki/Zork). I believe the first time I have played Zork was around 1984 on a Commodore 64.

Zork

Zork

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McuOnEclipse Components: 30-Sept-2018 Release

I’m pleased to announce a new release of the McuOnEclipse components, available on SourceForge. This release includes several bug fixes, extra support for the NXP S32 Design Studio and SDK and includes FreeRTOS V10.1.1.

SourceForge

SourceForge

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Porting Processor Expert Projects to MCUXpresso IDE

The McuOnEclipse GitHub repository hosts many Processor Expert projects and is very popular (cloned more than 1000 times, thank you!). Processor Expert is a powerful framework which generates driver and configuration code, simplifying application development for a wide range of microcontroller and families. But Processor Expert won’t be developed further by NXP and is not part of MCUXpresso IDE. While it is possible to install Processor Expert into MCUXpresso IDE 10.2, how can these projects used ini an IDE *without* Processor Expert? This article describes how to port an existing Processor Expert project into the NXP MCUXpresso IDE.

Adafruit SSD1351 with FRDM-K64F

Ported Project with FRDM-K64F using Adafruit SSD1351 and Processor Expert

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Using custom FreeRTOS with S32K SDK and OSIF for ARM

In “Tutorial: FreeRTOS 10.0.1 with NXP S32 Design Studio 2018.R1” I showed how to use a custom FreeRTOS with the S32 Design Studio (ARM). The OSIF (OS Interface) provides an operating system and services abstraction for the application which is used by other S32K SDK components:

OSIF in S32K for ARM Eclipse Project

OSIF in S32K for ARM Eclipse Project

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Tutorial: FreeRTOS 10.0.1 with NXP S32 Design Studio 2018.R1

NXP not only sells general purpose microcontroller, but as well a portfolio of automotive devices which includes the S32K which is ARM Cortex based. For this device family, they offer the S32 Design Studio (or S32DS) with its own Eclipse distribution and SDK. The interesting part is that the S32DS includes Processor Expert (which is a bit different from the ‘mainstream’ Processor Expert). It comes with its own components for the S32K SDK which includes a component for FreeRTOS. But that component in S32DS 2018.R1 comes with an old V8.2.1 FreeRTOS component:

FreeRTOS 8.2.1 in S32DS 2018.R1

FreeRTOS 8.2.1 in S32DS 2018.R1

So what to do if I want to use the latest FreeRTOS (currently 10.0.1) with all the bells and whistles?

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McuOnEclipse Components: 1-July-2018 Release

I’m pleased to announce that a new release of the McuOnEclipse components is available on 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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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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Sneak Preview: DIY SMT Pick & Place Machine with OpenPnP

I apologize: I have not been blogging much in the past weeks :-(. One reason is that I’m working on a DIY SMT/SMD Pick&Place machine which keeps me busy most of my spare time :-). I admit that this project is not finished yet, but now is the time I can give a sneak preview: a SMD/SMT pick and place machine:

Pick&Place Machine

Pick&Place Machine

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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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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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Faster FreeRTOS Percepio Tracealyzer Streaming with Segger RTT

To solve the real hard problem of Embedded Systems development, I usually need all the data I can get from the target. The Percepio Tracealizer is such a tool which can stream application and FreeRTOS trace from the target over a Segger J-Link connection using the Segger RTT protocol. I’m using that combination a lot.

Streaming trace data that way does not need a dedicated hardware like ETM Trace. Using RTT is usually not much intrusive and affects the performance of the target in the 1-2% range (of course depending on the amount of data).

But what worried me for several weeks is that after moving to FreeRTOS V10.0.0 and the same time updating the Segger libraries, the target performance was heavily affected:

RTT Streamnig affects target performance

RTT streaming affects target performance?

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McuOnEclipse Components: 26-Dec-2017 Release

I’m pleased to announce that a new release of the McuOnEclipse components is available in SourceForge., which is supposed to be the last release for 2017 :-). This release features several smaller bug fixes, the new FreeRTOS V10.0.0 and extended device support.

SourceForge

SourceForge

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