Shields

Shields, also known as “add-on” or “daughter boards”, attach to a board to extend its features and services for easier and modularized prototyping. In Zephyr, the shield feature provides Zephyr-formatted shield descriptions for easier compatibility with applications.

Shield porting and configuration

Shield configuration files are available in the board directory under /boards/shields:

boards/shields/<shield>
├── <shield>.overlay
└── dts_fixup.h

These files provides shield configuration as follows:

  • <shield>.overlay: This file provides a shield description in device tree format that is merged with the board’s device tree information before compilation.
  • dts_fixup.h: This is a fixup file to bind board components definitions with application in a generic fashion to enable shield compatibility across boards

Board compatibility

Hardware shield-to-board compatibility depends on the use of well-known connectors used on popular boards (such as Arduino and 96boards). For software compatibility, boards must also provide a configuration matching their supported connectors.

This should be done at two different level:

  • Pinmux: Connector pins should be correctly configured to match shield pins
  • Device tree: A board device tree file should define a node alias for each connector interface. For example, for Arduino I2C:
#define arduino_i2c i2c1

aliases {
        arduino,i2c = &i2c1;
};

Note: With support of dtc v1.4.2, above will be replaced with the recently introduced overriding node element:

arduino_i2c:i2c1{};

Shield activation

Activate support for a shield by adding the matching -DSHIELD arg to CMake command

# On Linux/macOS
cd $ZEPHYR_BASE/your_app
mkdir build && cd build

# On Windows
cd %ZEPHYR_BASE%\your_app
mkdir build & cd build


# Use cmake to configure a Ninja-based build system:
cmake -GNinja -DSHIELD=x_nucleo_iks01a1 ..

# Now run ninja on the generated build system:
ninja

Alternatively, it could be set by default in a project’s CMakeLists.txt:

set(SHIELD x_nucleo_iks01a1)