Driver Transport Example

Reviewed on: 2024-10-14

This example demonstrates a parent driver that implements and serves the driver transport FIDL protocol, fuchsia.hardware.i2cimpl, and a child driver that connects to the protocol to interact with the parent.

Building

To include the driver to your build, append --with //examples/drivers/transport/driver:drivers to your fx set command. For example:

$ fx set core.x64 --with //examples/drivers/transport/driver:drivers
$ fx build

Running

Register the parent driver by running this command

$ ffx driver register fuchsia-pkg://fuchsia.com/driver_transport_parent_pkg#meta/parent-driver.cm

Register the child driver by running this command

$ ffx driver register fuchsia-pkg://fuchsia.com/driver_transport_child_pkg#meta/child-driver.cm

Verify that both drivers show up in this command

ffx driver list

Add a test node that binds to the parent driver:

$ ffx driver test-node add driver_transport_parent gizmo.example.TEST_NODE_ID=driver_transport_parent

Run the following command to verify that the driver is bound to the node:

$ ffx driver list-devices -v transport

You should see something like this:

Name     : driver_transport_parent
Moniker  : dev.driver_transport_parent
Driver   : fuchsia-pkg://fuchsia.com/driver_transport#meta/driver_transport_parent.cm
1 Properties
[ 1/  1] : Key "gizmo.example.TEST_NODE_ID"   Value "driver_transport_parent"
0 Offers

Name     : driver_transport_child
Moniker  : dev.driver_transport_parent.driver_transport_child
Driver   : fuchsia-pkg://fuchsia.com/driver_transport#meta/driver_transport_child.cm
1 Properties
[ 1/  1] : Key "fuchsia.hardware.i2cimpl.Service" Value "fuchsia.hardware.i2cimpl.Service.DriverTransport"
1 Offers
Service: fuchsia.hardware.i2cimpl.Service
  Source: dev.driver_transport_parent
  Instances: default

Name     : transport-child
Moniker  : dev.driver_transport_parent.driver_transport_child.transport-child
Driver   : unbound
0 Properties
0 Offers

Testing

Include the tests to your build by appending --with //examples/drivers:tests to your fx set command. For example:

$ fx set core.x64 --with //examples/drivers/transport/driver/v2:driver-transport-test
$ fx build

Run unit tests with the command:

$ fx test driver_transport_example_test

The unit test sets up a fake driver transport server for the child driver and verifies that the driver successfully queried the values from the server.

Source layout

The core implementation of the parent driver is in parent-driver.cc and the child driver is in child-driver.cc. Unit tests are located in tests.