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docs: add hdmi-cec interface documentation #606

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36 changes: 36 additions & 0 deletions docs/reference/interfaces/hdmi-cec-interface.md
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(interfaces-hdmi-cec-interface)=
# hdmi-cec interface

The `hdmi-cec` interface allows a snap to communicate with HDMI Consumer Electronics Control (CEC) devices through a system CEC adapter.
It is intended for snaps that need to send commands to, or receive events from, HDMI-connected equipment such as televisions and audio systems.

The interface provides an implicit system slot on Ubuntu Core and classic systems.
The interface is not auto-connected; the user must connect the application plug to the system slot manually.

An application snap declares the plug:

```yaml
apps:
controller:
plugs: [hdmi-cec]
```

Connect the plug to the implicit system slot with:

```bash
snap connect controller-snap:hdmi-cec :hdmi-cec
```

The interface grants access to Linux CEC device nodes such as `/dev/cec0`, as well as legacy platform-specific nodes including `/dev/hdmicec`, `/dev/CEC`, `/dev/aocec`, `/dev/mxc_hdmi_cec`, `/dev/tegra_cec`, and Raspberry Pi's `/dev/vchiq`.
It also permits the CEC sysfs discovery and metadata access needed by CEC libraries and selected legacy backends.
The available node depends on the hardware, kernel, and enabled driver; not every system provides all of these paths.

USB-attached serial CEC adapters are not covered by `hdmi-cec`. Use the {ref}`raw-usb interface <interfaces-raw-usb-interface>` for USB device access.

**Auto-connect**: no

This interface has no plug or slot attributes. Hardware access still requires a supported CEC adapter and driver on the system.

The test code can be found in the snapd repository: [hdmi_cec_test.go](https://github.com/canonical/snapd/blob/master/interfaces/builtin/hdmi_cec_test.go).

The source code for the interface is in the snapd repository: [hdmi_cec.go](https://github.com/canonical/snapd/blob/master/interfaces/builtin/hdmi_cec.go).
1 change: 1 addition & 0 deletions docs/reference/interfaces/index.md
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Expand Up @@ -93,6 +93,7 @@ The following column names are used:
| {ref}`hardware-observe <interfaces-hardware-observe-interface>` | access hardware information | System, Hardware | no |
| {ref}`hardware-random-control <interfaces-hardware-random-control-interface>` | provide entropy to hardware random number generator | System, Hardware | no |
| {ref}`hardware-random-observe <interfaces-hardware-random-observe-interface>` | use hardware-generated random numbers | System, Hardware | no |
| {ref}`hdmi-cec <interfaces-hdmi-cec-interface>` | access HDMI CEC devices | Hardware, Developer | no |
| {ref}`hidraw <interfaces-hidraw-interface>` | access hidraw devices | System | no |
| {ref}`home <interfaces-home-interface>` | access non-hidden files in the home directory | Storage, Personal data | yes on classic (traditional distributions), no otherwise |
| {ref}`hostname-control <interfaces-hostname-control-interface>` | allows configuring the system hostname | Network | no |
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