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FreeRTOS tutorial on STM32

A High-density line of STM32 microcontrollers has quite many features that can be used in your programs. However, the more features you add to the source, the more complicated the program becomes, and it may become challenging to keep up with all things. Relying on the main loop and interrupts becomes a time-consuming task to manage. If you do not want to struggle while tuning things up manually, you can use one of the best free real-time operating systems (RTOS). It is handy when you need many separate functions to run in parallel without missing a task. RTOS scheduler takes care of giving each task a required period to perform. There are many great RTOS systems around. Many of them are free and open source. Follow the FreeRTOS tutorial to see how easy it is to run complex tasks. I love using FreeRTOS, which has a long successful history and is flexible to fit multiple hardware types. You can check out my demo FreeRTOS tutorial on Atmega128. I also encourage you to give it a try for other RTOS systems like ChibiOS, BeRTOS, and others. FreeRTOS is quite simple and easy to use. It has practically all of the features…

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Flashing programs to STM32. Embedded Bootloader

Post updated with new screens and up-to-date information (2020)! There have been several requests from users to explain more about loading programs into the flash memory of STM32 microcontrollers. There are several ways on how to perform stm32 flash programming. You may enter the STM32 bootloader directly via USART interface and upload the binaries. The more advanced and flexible method is to use an ST-LINK utility – an ST-based adapter, which connects to STM32 board through JTAG interface. Many ST development boards already have this feature included. Otherwise, you can jump-wires from one to another, or get a dedicated portable ST-Link adapter. Also, you can use standard third-party JTAG tools such as J-Link. Finally, you can flash your bootloader that works with any interface (USART, USB, SPI, etc.) The STM32F103RB board Any of these methods are great if they get the job done. In this topic, let us focus on how to perform STM32 flashing by using a bootloader. Today probably, no manufacturer is producing developing boards with RS232 interface. Nevertheless, you like me, probably have a dozen older boards with a serial port. They are great boards still to use in many projects.

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Pushing prototyping with STM32F4Discovery to new level

STM32F4Discovery board is already quite powerful and stacked with many handy features. On a single board, you can find a three-axis accelerometer, MEMS microphone, DAC with D class amplifier that can output sound through the built-in audio jack. Also, there are a couple of LEDs and a button for fast access. And of course, the core of this board is STM32F407VGT6 ARM Cortex-M4 microcontroller that packs series of great features including DSP instructions and floating point unit. But eventually, with such power, you will miss several other handy features that could be used in your project. Think of LCD, Ethernet, RS232 interface and even camera. You could start making your extension boards that include additional features, but why bother, since there already are several extension boards available for it. Let us go through them and see the features you could get without a heating soldering iron.

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Setting up CoIDE with GNU tools

For some time I’ve been using Codebench ARM GCC tools for developing software for ARM microcontrollers. As IDE I used plain Eclipse which I had to configure by myself. It worked pretty well, and there is nothing wrong with this. Anyway, sometimes it gets a little annoying to keep an eye on configurations and manual settings. So I decided to give a try CooCox IDE which claims to be free and open. It seems that already supports all the microcontrollers I like to use. Along to this change, I am also moving to a different GCC tool collection. Codebench free tools are great, but on another hand, there are some limitations. One of them is release times. They are releasing their free tools twice a year, so updates and other improvements cannot reach as fast as you’d expect. Another thing I am concerned – disabled hard float functionality. If you would like to ta take advantage of floating point unit in Cortex-M4, then you get stuck. If you are not using hardware floating point module, then this tool works fine, and you can stick with it. Anyway, I don’t like limitations, especially with free tools, so I am switching to…

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You know basics of ARM. Whats next?

You’ve probably noticed that day by day more complex hardware gets closer to a user. Of course, I am talking about microcontrollers and processors. Several years ago it was a challenge to have running Linux on board. Now almost everyone has Raspberry Pi and doing crazy things. As I have noticed not many hobbyists are building their boards to get things done. There is a wide variety of ready made developing boards depending on size, speed, price that it looks not worth spending time on what’s already done. Everyone seems to be grabbing Arduino and building amazing projects. In a couple of years, enthusiasts used to crunch ARM projects like cookies. This is thanks to the choice of cheap development boards and improving free software tools. But the most critical role in this is the manufacturers. They finally noticed that hobby market could be a powerful driving mechanism. Ignoring it means losing the game. Now almost every hardware company is trying to get their development board closer to maker and hacker community. Because they like to build stuff and spread the word about it.

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Bit Band operations with ARM Cortex microcontrollers

I got few questions from our readers about the bit-band feature in ARM Cortex microcontrollers. It may seem to be a prominent topic, still may lead to come confusion while using bit-banding. So let’s look at this feature a little bit closer. Why use bit band? Simply speaking Bit banding method allows performing atomic bitwise operations to memory areas. Why use bit banding? The most straightforward answer is because ARM Cortex doesn’t have something like BIT CSET or BIT CLEAR commands like most of the 8-bit microcontrollers do. So this is somewhat a workaround solution. Another question may rise – Why not using the read-modify-write method? Again this method is not reliable in some cases. For instance, f there is an interrupt during this operation; it can cause data corruption. Other situation may occur in embedded OS when different tasks may modify the same memory location. So we want a method that allows setting or clear individual bits with a single instruction. This is where the bit band method helps.

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Basic touch screen routines up and running

STm32 touch screen

STM32103ZET6 prototyping board comes with LCD having touch screen capability. It is a great way to interact with the device. Practically speaking Touch screen is a resistive film that can be accessed as a regular potentiometer which value depends on touch point. Depending on voltage drop it is possible to calculate the coordinates. There is a touch screen controller which takes most of the hard work – it has internal ADC that measures the voltage and sends a value to the microcontroller using one of the selected interfaces (I2C or SPI). In the board, there is a common ADS7843 controller used, which talks to the microcontroller using SPI. After playing around, I’ve put a messy code that reads touch screen coordinates. It is a glued code from various sources, so it is only to fix some results. Currently, the code reads a bunch of values, then averages to get rid of most garbage and then calculates screen matching coordinates. This is the trickiest part to do. You can do this empirically by reading min and max ADC values for each axis and then calculate coordinates using formulas:

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Updating STM32 C template with CMSIS V3

So far we’ve been using an old template with CMSIS version 1.30. Since then it was updated several times by adding support of new Cortex processor families, fixing several bugs and adding new features. They also changed the folder structure of CMSIS to be more generic. And there is a CMSIS DSP library integrated. With it, you can do complex math tasks using only a few lines of code. So why not upgrading our software template for Sourcery Codebench G++ toolchain with new CMSIS. Also, we are going to get rid of external makefile with ARM GCC Eclipse plug-in. How to install and use this plugin we discussed in previous posts (part1 and part2). First of all download the latest CMSIS package from arm.com/cmsis. You will have to register to access download files. Package with CMSIS, DSP library and documentation weights about 45MB. Since we are working with ST32 microcontrollers, you also need to download STM32F10x Standard Peripheral Library from STMicroelectronics.

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Setting up Eclipse to work with GNU ARM plug-in. Part 2.

Continue of part 1. First of all, let us select the proper processor type. Using the Cortex-M3 processor, we go to the Project->Properties menu (or right-click on the project name in the project explorer and select Properties). First in the Tool Settings list is Target Processor. So we select processor cortex-m3: Be sure to choose settings for all configurations, so you don’t have to do this twice when selecting Debug or Release.

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Setting up Eclipse to work with GNU ARM plug-in. Part 1.

Eclipse is an excellent multiplatform graphical interface practically for any language. If you choose to use it – you won’t loose. We’ve been using it when writing software for ARM microcontrollers. As compiler Mentor Graphics Sourcery Codebench Lite works just fine. If you have both – Eclipse and Sourcery tools installed we can move on. So far in our earlier project we’ve been using an external makefile project setup. This means that we had to write/edit makefile in order to compile and link project files. This is hand job and requires some knowledge and time. You cannot run away from them if you are using free tools, but there should be some way out and automate at least some parts of this work. Eclipse Indigo comes with CDT C/C++ development tools. It works excellent with general C/C+ projects and we’ve been using it without problem along with external makefile and project settings. But there is a better way of developing project for ARM platforms. It’s GNU ARM Eclipse Plug-in. It supports most of GNU toolchains including Sourcery Codebench Lite, Yagarto, GNUARM, WinARM and other. So lets set up Eclipse to use this plugin and see how it works.

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