Project structure – where things go?

Aery32 Software Framework provides a complete project structure to start AVR32 development right away. You just start coding and adding your files. The default project directory structure looks like this:


It is intended that you work under the root directory most of the time as that is the place where you keep adding your .c, .cpp and .h source files. Notice that Aery32 Framework is a C/C++ framework and thus you can write your code in both C and C++. Just put the C code in .c files and C++ code in .cpp files.

The following subsections define each part of the default project structure in alphabetic order as they are listed above.

Aery32 library, aery32/

The directory called aery32/ contains the source files of the Aery32 library. The archive of the library (.a file) appears in this directory after the first compile process. The aery32/ subdirectory within the aery32/ contains the header files of the library. Additionally, linker scripts, which are essential files to define the MCU memory structure are kept under this directory. Take a look at the ldscripts/ subdirectory if you are curious.


Although you can, you should not need to hassle with any file under this directory.

Main source file, main.cpp

The main.cpp source file contains the default main function where to start building your project. First the board.h header file has been included. This file includes your application specific function prototypes, which are defined in board.cpp. For your convenience a small board::init() function is provided by default. This function is called within the main function at line 11. It’s the first function call here. The second call is to set the LED pin high.

#include "board.h"
using namespace aery;

int main(void)
     * Put your application initialization sequence here. The default
     * board initializer defines the LED pin as output and sets the CPU
     * clock speed to 66 MHz.

    for(;;) {
        /* Put your application code here */


    return 0;

Board specific functions, board.h and .cpp

Use these two files for your board specific functions and macro definitions. A macro definition is for example the following pin declaration

#define LED    AVR32_PIN_PC04

Now you don’t have to always recall which pin the LED was connected when you want to switch it on. So instead of using this


you can use this


You can find this default LED macro definition from board.h. There are also other default board related definitions, which you may need to change according to your project. Those are for example

#define ADC_VREF    3.0
#define ADC_BITS    10

These two macro definitions are related to the analog to digital converter (ADC). To change the reference voltage of the ADC, modify the ADC_VREF. Similarly if you decide to use, for example, only eight bits accuracy alter ADC_BITS accordingly. You may like to reduce the accuracy in favor throughput rate of the analog to digital converter. With smaller accuracy ADCs generally work faster.

From these ADC related settings, we get to one of the functions declared in the default version of board.h. That’s board::cnv2volt().

static inline double cnv2volt(uint32_t cnv)
    return cnv * ((double) ADC_VREF / (1UL << ADC_BITS));

This function han’t been declared in a library because it’s highly dependant of the reference voltage and accuracy of ADC. Note how it uses ADC_VREF and ADC_BITS internally to calculate the correct voltage for the conversion.

It’s intended that you define all your board related functions in board.h and then implement those in board.cpp. Example programs coming with the framework are built in one file with the main function in purpose, but when used in real application those should be refactored into board.h and .cpp.

For example, consider that you had a device which to communicate via SPI. To take an advance of the board abstraction you could write a function like this

uint8_t board::write_to_device(uint8_t byte)
    return aery::spi_transmit(spi0, 2, byte);

See how the above function abstracts which SPI and slave select you are using.

Default board initializer

The default board initializer function, board::init(), can be found from the board.cpp source file. The prototype of this function is declared in board.h.

Here’s what it basicly does by default

  • Sets all GPIO pins inputs
  • Defines LED pin as output
  • Starts the external oscillator OCS0
  • Sets the chip’s master (or main) clock frequency to its maximum, which is 66 MHz

If you like to change the master clock frequency or want to change the way how the board is initialized, board::init() is the place where to do it.


All board related functions should use a namespace board to not introduce any name collision with other functions added into the project.

Build system, Makefile

Makefile contains all the make recipes for compiling the project and uploading the compiled binary to the board. See more detailed instructions from the build system section.


Generally Makefiles don’t have a file postfix like .cpp and it’s a common practice to start its name with capital M.

Project wide settings, settings.h

In this file you can define project wide global settings. Aery32 Framework is also aware some of the settings defined in this file. For example, to get the delay functions work properly you have to define the correct CPU frequency, F_CPU, in this file. Below you can see how some essential settings have been defined.

#define F_OSC0 12000000UL
#define F_OSC1 16000000UL
#define F_CPU  66000000UL


This file is provided to GCC via -include