doc: Update mainpage

Martine Lenders 8 years ago committed by Martine Lenders
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@ -3,273 +3,243 @@ RIOT Documentation {#mainpage}
RIOT is an operating system designed for the particular requirements of Internet
of Things (IoT) scenarios. These requirements comprise a low memory footprint,
high energy efficiency, real-time capabilities, a modular and configurable
communication stack, and support for a wide range of low-power devices. RIOT
provides a microkernel, utilities like cryptographic libraries, data structures
(bloom filters, hash tables, priority queues), or a shell, different network
stacks, and support for various microcontrollers, radio drivers, sensors, and
configurations for entire platforms, e.g. Zolertia Z1 or STM32 Discovery
The microkernel itself comprises thread management, a priority-based scheduler,
a powerful API for inter-process communication (IPC), a system timer, and
In order to build an application or library with RIOT, you need first to
download the source code ([Getting the source
code]( This contains - besides the
before mentioned features - also some example applications (located in the
`examples` subdirectory) and a sample Makefile you may use for your own
project. This Makefile template shows you how to compile and link your application
against RIOT ([Compiling RIOT](
If you want to use RIOT directly with your embedded platform, you need to
install the corresponding toolchain for the deployed microcontroller ([ARM
based platforms](, [TI MSP430 based
### Native RIOT - Run RIOT on your PC!
As a special platform, you will find a CPU and board called `native` in the
repository. This target allows you to run RIOT as a process on Linux on most
supported hardware platforms. Just set `BOARD = native` in your
application's Makefile, call `make`, and execute the resulting elf-file. Further
documentation about the native port can be found in `cpu/native/`.
The RIOT repository contains the following ten subdirectories:
* boards
* core
* cpu
* dist
* doc
* drivers
* examples
* pkg
* sys
* tests
The `boards` directory provides the configurations and initialization code for
supported IoT platforms. In `core` you can find the kernel, while `cpu`
comprises microcontroller specific implementations like startup and exception
handling code. The directory `dist` contains a template for an application's Makefile
and external utilities like the terminal program `pyterm` or a script to build
your own toolchain for ARM microcontrollers. Not very surprisingly you will find
the (doxygen) documentation in `doc` and peripheral driver code in `drivers`.
The `examples` directory provides some exemplary applications, `pkg` includes
Makefiles to integrate external libraries into RIOT, and `sys` system libraries
as well as the implementation of the network stacks which are located in
`sys/net`. Finally, the subdirectory `tests` contains test applications,
including also a few expect scripts to automatically validate some of them.
int main()
puts("Hello World!");
return 0;
Getting the source code
You can obtain the latest RIOT code from our [Github](
repository either by [downloading the latest tarball](
or by cloning the [git repository](
In order to clone the RIOT repository, you need the [Git revision control
system]( and run the following command:
git clone git://
The repository contains the kernel, support for different CPUs and platforms, device
drivers, system libraries, and network stack implementations. Inaddition it comprises
various example applications to demonstrate the usage ofsome important features.
It also provides you with useful tools like a terminal program and scripts to
setup a toolchain.
Compiling RIOT
Depending on the hardware you want to use, you need to first install a
corresponding toolchain:
* [ARM-based platforms](
* [TI MSP430](
* [Atmel ATmega](
* [native](
### Create an application
Once you have set up the toolchain, you can create your own application. Apart from
the C file(s) containing your source code you need a Makefile. A template
Makefile is available in the `dist` folder of the
[RIOT repository](
Within your application's Makefile, you can define the target hardware as well as
the modules you want to use.
Unless specified otherwise, make will create an elf-file as well as an Intel
hex file in the `bin` folder of your application directory.
Special features
The build system
RIOT uses GNU make as build system. The simplest way to compile and link an
application (or library) with RIOT, is to set up a Makefile providing
at least the following variables:
* `APPLICATION`: should contain the (unique) name of your application
* `BOARD`: specifies the platform the application should be build for by default
* `RIOTBASE`: specifies the path to your copy of the RIOT repository
(note, that you may want to use `$(CURDIR)` here, to give a relative path)
Additionally it has to include the `Makefile.include`, located in RIOT's root
directory. You can use Make's `?=` operator in order to allow overwriting
variables from the command line. For example, you can easily specify the target
platform, using the sample Makefile, by invoking make like this:
make BOARD=iotlab-m3
Besides typical targets like `clean`, `all`, or `doc`, RIOT provides the special
targets `flash` and `term` to invoke the configured flashing and terminal tools
for the specified platform. These targets use the variable `PORT` for the serial
communication to the device. Neither this variable nor the targets `flash` and
`term` are mandatory for the native port.
For the native port, `PORT` has a special meaning: it is used to identify the tap
interface if the @ref netdev2_tap module is used. The target `debug` can be used
to invoke a debugger on some platforms. For the native port the additional targets
such as `all-valgrind` and `valgrind` exist. Refer to `cpu/native/` for
additional information
Some RIOT directories contain special Makefiles like `Makefile.base`,
`Makefile.include` or `Makefile.dep`. The first one can be included into other
Makefiles to define some standard targets. The files called `Makefile.include`
are used in `boards` and `cpu` to append target specific information to
variables like `INCLUDES`, setting the include paths. `Makefile.dep` serves to
define dependencies.
Learn more about the build system in the
Including modules
By default a RIOT application comprises only the applications' code itself, the kernel,
and platform specific code. In order to use additional modules, such as a
particular device driver or a system library, you have to append the modules'
names to the USEMODULE variable. For example, to build an application using the SHT11
temperature sensor and UDP/IPv6 network stack, your Makefile needs to contain
these lines:
USEMODULE += sht11
USEMODULE += gnrc_ipv6_default
USEMODULE += gnrc_udp
To contribute a new module to RIOT, your module's Makefile needs to set the
variable `MODULE` to a unique name. If the module depends on other modules, this
information needs to be added to RIOT's `Makefile.dep`.
The main function
After the board is initialized, RIOT starts two threads: the idle thread and the
main thread. The idle thread has the lowest priority and will run, whenever no
other thread is ready to run. It will automatically use the lowest possible
power mode for the device. The main thread - configured with a default priority
that is right in the middle between the lowest and the highest available
priority - is the first thread that runs and calls the main function. This
function needs to be defined by the application.
Choosing the right stack size
Choosing the right stack size for a new thread is not an easy, but a very
crucial task. Since memory is usually a scarce resource in IoT scenarios,
one must be careful not to assign too much stack to a single thread.
However, if you allocate too little memory for a stack, your application
will probably crash. The minimum stack size depends also on some RIOT
internal structs and is hardware dependent. In order to help developers
finding the right stack size, RIOT defines some typical stack sizes in
`cpu_conf.h` (which should be provided by the implementation for all
supported MCUs). The constants for these stack sizes are
and can be used by including `kernel.h`. ARM based platforms additionally
define `THREAD_EXTRA_STACKSIZE_PRINTF_FLOAT`, because newlib's `printf`
implementation uses more memory for printing floating point numbers.
`THREAD_STACKSIZE_IDLE` is the stack size for the idle thread and
probably the smallest sensible stack size. `THREAD_STACKSIZE_DEFAULT`
is a default size for any typical thread, *not* using `printf`.
`THREAD_EXTRA_STACKSIZE_PRINTF` defines additional stack space needed if the
thread needs to call printf (which requires additional memory when using
newlib). `THREAD_STACKSIZE_MAIN` is the stack size for the main thread
and probably a good size for your application. (Note, that on most
non-newlib dependent platforms this will probably equal
RIOT in a nutshell {#riot-in-a-nutshell}
RIOT is an open-source microkernel-based operating system, designed to match
the requirements of Internet of Things (IoT) devices and other embedded
devices. These requirements include a very low memory footprint (on the order
of a few kilobytes), high energy efficiency, real-time capabilities,
communication stacks for both wireless and wired networks, and support for a
wide range of low-power hardware.
RIOT provides a microkernel, multiple network stacks, and utilities which
include cryptographic libraries, data structures (bloom filters, hash tables,
priority queues), a shell and more. RIOT supports a wide range of
microcontroller architectures, radio drivers, sensors, and configurations for
entire platforms, e.g. Atmel SAM R21 Xplained Pro, Zolertia Z1, STM32 Discovery
Boards etc. (see the list of
[supported hardware](
Across all supported hardware (32-bit, 16-bit, and 8-bit platforms). RIOT
provides a consistent API and enables ANSI C and C++ application programming,
with multithreading, IPC, system timers, mutexes etc.
Contribute to RIOT {#contribute-to-riot}
RIOT is developed by an open community that anyone is welcome to join:
- Download and contribute your code on
[GitHub]( You can read about how to
contribute [in our GitHub
- [Subscribe]( to to ask for help using RIOT or writing an application for
RIOT (or to just stay in the loop). A searchable archive of this list is
available at the
[RIOT user Gmane newsgroup](
- [Subscribe](( to to follow and discuss kernel and network stack
developement, or hardware support. A searchable archive of this list is
available at the
[RIOT devel Gmane newsgroup](
- Follow us on [Twitter]( for news from the RIOT
- Contact us on IRC for live support and discussions:
[ #riot-os](irc://
The quickest start {#the-quickest-start}
You can run RIOT on most IoT devices, on open-access testbed hardware (e.g.
IoT-lab), and also directly as a process on your Linux/FreeBSD/OSX machine (we
call this the `native` port). Try it right now in your terminal window:
git clone git:// # assumption: git is pre-installed
git checkout <LATEST_RELEASE>
./dist/tools//tapsetup/tapsetup # create virtual Ethernet
# interfaces to connect to RIOT
cd examples/default/
make all
make term
... and you are in the RIOT shell!
Type `help` to discover available commands. For further information see the
[README of the `default` example](
To use RIOT directly on your embedded platform, and for more hands-on details
with RIOT, see [TODO: link to getting started guide].
Before that, skimming through the next section is recommended (but not
Structure {#structure}
Like any microkernel system, RIOT has an IPC API that enables data exchange
between modules or a single module and the kernel. This API is documented in
@ref core_msg. The IPC can be used in several ways, such as synchronous or
asynchronous, blocking or non-blocking, with or without a message queue. In
the default case, a thread does not have a message queue. Hence, messages
sent in a non-blocking manner are lost, when the target thread is not in
receive mode. A thread may set up a message queue using the msg_init_queue()
function, but has to provide the memory for this queue itself.
This section walks you through RIOT's structure. Once you understand this
structure, you will easily find your way around in RIOT's code base.
RIOT's code base is structured into five groups.
<!-- TODO: add graphic -->
- The kernel (`core`)
- Platform specific code (`cpu`; `boards`)
- Device drivers (`drivers`)
- Libraries and network code (`sys`; `pkg`)
- Applications for demonstrating features and for testing (`examples`;
In addition RIOT includes a collection of scripts for various tasks (`dist`) as
well as a predefined environment for generating this documentation (`doc`).
The structural groups are projected onto the directory structure of RIOT, where
each of these groups resides in one or two directories in the main RIOT
The following list gives a more detailed description of each of RIOT's
top-level directories:
This directory contains the actual kernel. The kernel consists of the
scheduler, inter-process-communication (messaging), threading, thread
synchronization, and supporting data-structures and type definitions.
See @ref core for further information and API documentations.
The platform dependent code is split into two logic elements: CPUs and boards,
while maintaining a strict 1-to-n relationship, a board has exactly one CPU,
while a CPU can be part of n boards. The CPU part contains all generic, CPU
specific code (see below).
The board part contains the specific configuration for the CPU it contains.
This configuration mainly includes the peripheral configuration and
pin-mapping, the configuration of on-board devices, and the CPU's clock
On top of the source and header files needed for each board, this directory
additionally may include some script and configuration files needed for
interfacing with the board. These are typically custom flash/debug scripts or
e.g. OpenOCD configuration files. For most boards, these files are located in a
`dist` sub-directory of the board.
See here @ref boards for further information.
For each supported CPU this directory contains a sub-directory with the name of
the CPU. These directories then contain all CPU specific configurations, such
as implementations of power management (LPM), interrupt handling and vectors,
startup code, clock initialization code and thread handling (e.g. context
switching) code. For most CPUs you will also find the linker scripts in the
`ldscripts` sub-directory.
In the `periph` sub-directory of each CPU you can find the implementations of
the CPU's peripheral drivers like SPI, UART, GPIO, etc. See @ref driver_periph
for their API documentation.
Many CPUs share a certain amount of their code (e.g. all ARM Cortex-M based
CPUs share the same code for task switching and interrupt handling). This
shared code is put in its own directories, following a `xxxxx_common` naming
scheme. Examples for this is code shared across architectures (e.g.
`cortexm_common`, `msp430_comon`) or code shared among vendors (e.g.
See @ref cpu for more detailed informtation.
This directory contains the drivers for external devices such as network
interfaces, sensors and actuators. Each device driver is put into its own
sub-directory with the name of that device.
All of RIOT's device drivers are based on the peripheral driver API (e.g. SPI,
GPIO, etc.) and other RIOT modules like the `xtimer`. This way the drivers are
completely platform agnostic and they don't have any dependencies into the CPU
and board code.
Most modules require initialization before they can be used. In some cases the
initialization function does not require a parameter. For these modules the
@ref sys_autoinit feature is included automatically. It calls all module
initialization functions with a `void` parameter just before the main thread
gets executed. You can deactivate this behavior (e.g. for testing) by adding
the line
See @ref drivers for more details.
DISABLE_MODULE += auto_init
RIOT follows the micro-kernel design paradigm where everything is supposed to
be a module. All of these modules that are not part of the hardware abstraction
nor device drivers can be found in this directory. The libraries include data
structures (e.g. bloom, color), crypto libraries (e.g. hashes, AES) ,
high-level APIs (e.g. Posix implementations), memory management (e.g. malloc),
the RIOT shell and many more.
to your Makefile.
See @ref sys for a complete list of available libraries
The `sys/net` sub-directory needs to be explicitly mentioned, as this is where
all the networking code in RIOT resides. Here you can find the network stack
implementations (e.g. the GNRC stack) as well as network stack agnostic code as
header definitions or network types.
See @ref net for more details on networking code.
RIOT comes with support for a number of external libraries (e.g.
[microcoap]( The way they are included is
that RIOT ships with a custom Makefile for each supported library that
downloads the library and optionally applies a number of patches to make it
work with RIOT. These Makefiles and patches can be found in the `pkg`
See @ref pkg for a detailed description on how this works.
Here you find a number of example applications that demonstrate certain
features of RIOT. The default example found in this directory is a good
starting point for anyone who is new to RIOT.
For more information best browse that directory and have a look at the
`` files that ship with each example.
Many features/modules in RIOT come with their own test application, which are
located in this directory. In contrary to the examples these tests are mostly
focusing on a single aspect than on a set of features. Despite for testing, you
might consider these tests also for insights on understanding RIOT.
dist & doc
Whether you are looking for help with writing an application for RIOT, want to
learn more about it, or just stay in the loop you are invited to join the
[RIOT-users mailing list](
For developers who want to participate and contribute to the kernel development
or integrate new MCU and platform support the
[RIOT-devel mailing list]( is
the right place.
All the tooling around RIOT can be found in these two folders.
`doc` contains the doxygen configuration and also contains the compiled doxygen
output after running `make doc`.
Lastly, the `dist` directory contains tools to help you with RIOT. These
the serial terminal application `pyterm`, generic scripts for flashing,
debugging, reseting (e.g. support for [OpenOCD](,
[Jlink](, as well as code enabling easy
integration to open testbeds such as the [IoT-LAB](
Furthermore you can find here scripts to do all kind of code and style checks.
Further information {#further-information}
Idea for this section: just name each of RIOT's main features/concepts and link
to an appropriate page with further information:
- Create an application
- Networking
- The `main()` function
- Make system
- Include modules
- Threading
- Choose the right stack size
- Auto initialization