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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Waveshare ePaper display library
I bought a pair of ePaper displays from Waveshare with the intent to use them in a wireless sensor network for displaying slowly changing data. The reference code from Waveshare is quite clunky and not so easy to re-use, so I made my own small, portable graphics library and display driver (with ARM Cortex-M in mind).
The library is available on Github.
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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
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1 2 |
/* Call static constructors */ bl __libc_init_array |
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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STM32L151 makefile project
I have published a basic Makefile project for STM32L151 on Github. I plan to develop it into a low-power wireless sensor network using SP1ML modules. The modules contains STM32L151RB MCU with 128K of flash, SPIRIT1 transceiver chip, antenna and passive components. Basically everything needed to make an 868MHz radio network.
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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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FreeRTOS on Kinetis E Cortex M0+ : easy porting tutorial
FreeRTOS is a popular, open-source operating system that can run on a variety of microcontrollers. This post shows how to make a minimal working setup with two tasks on a new MCU without starting from a complete demo code or code generators (like Processor Expert) on an inexpensive development board FRDM-KE06Z from NXP. All examples use static memory allocation. Most of the procedures and tips mentioned here apply equally well to all Cortex-M microcontrollers.
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XMEGA power down mode for battery powered devices
This post describes how to implement firmware-controlled device power switching on an XMEGA. I am working on a portable device that is powered from a Li-Ion cell, has an USB socket for charging, MCU, couple of LEDs and a button. I wanted to keep the design as simple as possible, so there is just one button connected to the MCU and no separate power switch. Most of the information applies equally to all AVR MCUs.
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Kinetis – relocating variables to upper SRAM
NXP Kinetis microcontrollers have an inconvenient architectural feature – split RAM. The memory is split into two areas of equal size. You can run into this issue when the size of all RAM variables (data+bss) approaches half size of available SRAM. It manifests itself with a linker error looking similar to this:
ld: region `m_data' overflowed by 132 bytes
I will use an MK22FN512 as an example, but this post applies equally to all Kinetis K-series MCUs.
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