Git – confirmation before commit

I use Git for version control of all my projects. Every repository of course has many branches that I try to systematize like: stable, devel, experimental, per-feature etc. Many times I have run into the problem of committing my changes to the branch I did not intended to. Git shows you the branch and changed files when entering the commit message, but when you do that 50 times a day you are doomed to loose focus (and commit your experimental stuff into a stable branch 🙂 ).

My solution to this problem is a simple pre-commit hook that reads the name of the branch and prompts for confirmation, if the name of the branch is on a watchlist.
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Using the internal EEPROM of STM32L

Most STM32 microcontrollers feature an internal EEPROM. It is useful for storing settings or calibration data. Regular flash (that stores code) can also be used, but the EEPROM can be updated byte-by-byte and is independent from regular flash. This may come handy during application updating, as whole flash can be simply erased without affecting the EEPROM.

I wrote a generic driver for keeping settings in the EEPROM based on the standard peripherals library for STM32L, that is easier to understand than the official demos from ST. It was tested on an STM32L151RC.
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Open OBD datalogger

This is a fully open-source car datalogger that reads engine data using the OBD2 interface in real time and stores it on an SD card. It also stores GPS data. All communication is done directly by the MCU without a translator chip like ELM327 or STN1110. The datalogger supports all CAN and K-Line OBD2 protocols. All hardware fits into an off-the-shelf OBD2 connector enclosure.


This project is available on Github.


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Kinetis E – writing to internal flash

While working on a bootloader for a Kinetis KE06 I obviously ran in to the task of having to write the internal flash memory of the microcontroller. Freescale’s driver is over 1500 lines of code, exposes every single bit of the flash controller so the simple operation of erasing a sector and writing to it requires many function calls. I wrote my own driver that is less than 200 lines of code and has everything needed to make a bootloader.
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Making graphics and fonts for embedded systems

Microcontroller systems with graphical displays require a way to display text. In case of alphanumeric displays (like HD44780) it is easy – just send your ASCII bytes to the display. Graphical displays operate on individual pixels, so firmware must generate the graphics and texts on the fly.

In this post I show the complete multi-step process from a TrueType (.ttf) font file to autogenerated C code that can be used by a graphics library to display texts on a microcontroller. All code (including the embedded graphics library) is available on Github.
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Hard fault in __libc_init_array

When starting my STM32 makefile project for the first time I encountered a very early hard fault in the startup code. It happened exactly when calling libc function at

The whole startup code came straight from ST, so I did not suspect it to be faulty. Here is what I have found out to fix the problem.
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Reading OBD2 data without ELM327, part 2 – K-Line

K-Line is another popular OBD2 interfacing standard, that has been used in European cars before CAN bus became common. There are a couple of physical variations (K-line, K+L, KKL) and slightly different protocols (KWP2000 or Keyword Protocol, and ISO 9141) running on those lines. Basically all you need to talk to an older car is an MCU with a UART and a single transistor. 🙂
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Reading OBD2 data without ELM327, part 1 – CAN

All modern cars have an OBD2 diagnostic connector that allows reading many engine and drivetrain parameters like RPM, vehicle speed, temperatures etc.

Most of car interfaces use a special protocol translating chip like ELM327 or STN1110 to convert different vehicle protocols (that depend on the age and brand of the car) into an easier to use serial protocol with AT-commands.

I wanted to build a datalogger that would fit into a OBD2 connector. There was no space to fit my microcontroller and another chip to do protocol conversion, so I investigated and reverse-engineered the most common OBD2 protocols to be able to implement them directly on my MCU.
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