Banjo Transport Driver Example

Reviewed on: 2024-02-27

This example demonstrates a parent driver serving a Banjo transport and a child driver that connects and queries data from it.

Building

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

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

Running

Register the parent driver by running this command

$ ffx driver register fuchsia-pkg://fuchsia.com/banjo_transport#meta/banjo_transport_parent.cm

Register the child driver by running this command

$ ffx driver register fuchsia-pkg://fuchsia.com/banjo_transport#meta/banjo_transport_child.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 banjo_transport_parent gizmo.example.TEST_NODE_ID=banjo_parent

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

$ ffx driver list-devices -v banjo_transport

You should see something like this:

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

Name     : banjo-transport-child
Moniker  : dev.banjo_transport_parent.banjo-transport-child
Driver   : fuchsia-pkg://fuchsia.com/banjo_transport#meta/banjo_transport_child.cm
3 Properties
[ 1/  3] : Key fuchsia.BIND_PROTOCOL          Value 0x00001c
[ 2/  3] : Key "gizmo.example.TEST_NODE_ID"   Value "banjo_child"
[ 3/  3] : Key "fuchsia.driver.compat.Service" Value "fuchsia.driver.compat.Service.ZirconTransport"
1 Offers
Service: fuchsia.driver.compat.Service
  Source: dev.banjo_transport_parent
  Instances: default

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:drivers --with //examples:tests
$ fx build

Run unit tests with the command:

$ fx test banjo_transport_example_test

The unit test sets up a fake banjo 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.