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Architecture Overview

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HDMI-CEC Profiles supported in RDK

Profiles

Description

Discovery

Discover HDMI devices that support CEC and provide settop information to those devices

Power

Synchronize settop power state with HDMI device power state

Switching

Switch settop HDMI inputs to settop HDMI outputs

Channel Change

Change channel on settop from HDMI device

Audio

Control audio mute/volume on HDMI device from settop and vice versa

User Input

Accept user input commands from HDMI device

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How HDMI-CEC Works in RDK

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Application API Specification

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  • The Library APIs allows application to contrl how the CEC stack operates, such as adding logical address to the stack.

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The Host interface allows libCEC implementation to interact with the host environment. Such interaction includes monitoring of the Power State change, the HDMI HotPlug events, or API to change the Host State. The Host Interface is delivered as a run-time plugin to the libCEC stack. This allows the CEC stack to run in any devices that implements the Host Interface.

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The relation between Application, Connection and CEC-Bus is described in the figure.

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CEC Daemon

  • This daemon receives Raw Bytes from the SoC Driver and dispatches them into IARM Bus via CecIARMMgr, it also receives Raw Bytes from IARM Bus and send to the SoC Driver. It controls the only access point to the physical HDMI CEC Bus.

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In essence, there is only one physical CEC bus on a system. However, with the help of Connection, Logical CEC-Bus, and IARM-Bus, the CEC library can converge the CEC traffic from different Connections and Logical Buses before forwarding them to the single physical bus. This is illustrated by the diagram below.

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In this diagram there are two applications (Receiver and CECDevMgr). Since both applications can only access the underlying physical CEC Bus via Connection API, they have no knowledge how the message are eventually delivered to the Physical Bus.

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The message flow on Connections and Logical Buses are full duplex.

Methods & Events

Following methods are used for DMI CEC module.

NameParametersDescription
setEnabledenabled : booleanEnables or disables CEC
getEnablednoneReturns true if CEC is enabled
setNamename : stringSets the name of the STB device.  The default name is "STB".  It is recommended that the name of the device is set prior to enabling CEC.
getNamenoneReturns the name of the STB device
sendMessage

message : String

The message is a base64 encoded byte array of the raw CEC bytes.  The CEC message includes the device ID for the intended destination.

getCECAddressesnone

return the JSON object <CECAddresses> that is assigned to the local device. It does not contain the <CECAddresses> of other devices on the connected CEC network.

"CECAddresses" : {
 "physicalAddress": Array of 4 bytes [byte0, byte1, byte2, byte3],
 "logicalAddresses" : Array of <CECLogicalAddress>
}
"CECLogicalAddress" : {
 "deviceType" : <string> 
 "logicalAddress": <integer>
}

The deviceType returned is part or all of devices types optionally set by XRE.

A CEC device can have multiple deviceTypes, if so an array of <CECLogicalAddress> with size more than one is returned.

Default deviceType is Tuner, and its logical Address is either 3, 6, 7, or 10.

In messages sent by XRE, XRE can only use the logicalAddress returned from CECAddresses.

Accepted deviceType are: "Tuner", "Record", "Playback", "AudioSystem", "VideoProcessor", "Switch"

Events notification:

Name

Content

Description

onMessage

message : String

Fired when a message is sent from an HDMI device.  Message is a base64 encoded byte array of the raw CEC bytes.

cecAddressesChangedJSON object <CECAddresses>Notify that address of the host CEC device has changed


API Documentation 

 To know more about SoC/Application level APIs details use in RDK, refer the link  RDK HDMI-CEC API Documentation