IT6620BFN: ARC/eARC Receiver with Audio MUX
The IT6620BFN is a receiver designed for HDMI 2.1 Enhanced Audio Return Channel (eARC) and it is also backward compatible to the HDMI 1.4 Audio Return Channel (ARC). When operating in eARC mode, the Differential Mode Audio Channel (DMAC) bandwidth, i.e. 98.304 Mbps, allows HDMI Sink to transmit 8-channel 192 K audio to the HDMI Source. No video stream and CEC function is required when eARC link is active.
The IT6620BFN adopts eight I2S and one SPDIF signals for the audio output interface. Eight I2S signals are used to transmit multi-channel L-PCM audio and the maximum 16-channel audio is supported by the IT6620BFN. When 16-channel audio is transmitted, the maximum audio sampling frequency is limited to 96 kHz because of the DMAC bandwidth limitation. Another available multi-channel interface is Time Division Multiplexed (TDM) interface which utilizes one I2S signal to transmit multi-channel audio, however, only 4/8/16-channel configuration is allowed. The SPDIF interface is used to transmit 2-channel compress audio, including High Bit Rate audio. A 128*Fs MCLK signal is also available for the SPDIF processor. Both I2S and SPDIF signals could be configured as DSD audio interface which is used to transmit One Bit Audio format and maximum 12-channel One Bit Audio layout is supported by the IT6620BFN.
In some systems, the output of IT6620BFN is connected to the audio processor which has only one audio input interface and needs to handle more than one audio input source. The IT6620BFN can multiplex external input audio with internal decoded audio and thus eliminates the necessary of extra audio MUX. The configuration of the embedded audio MUX is flexible and could be used for the most applications.
For the compress audio, 8-bit ECC syndrome is added to 16-bit audio data in the eARC TX, and 1-bit error in compress audio data could be corrected by HW in the IT6620BFN. To increase the security of the eARC audio transmission, a HW decryption mechanism is also implemented in the IT6620BFN. Because the content protection method is not a standard in eARC specification, the decryption mechanism of IT6620BFN is proprietary and only compatible with the ITE's eARC TX, such as IT6621. The FW of IT6621 would make sure the eARC RX is IT6620BFN before enabling the encryption option and this procedure can be done using Common Mode Data Channel (CMDC). Please refer to programming guide for the detail.
The CMDC in IT6620BFN provides bi-directional communication between eARC TX and RX. The Discovery and Disconnect process is implemented in HW and the FW can monitor the status by the interrupt and read back registers. In IT6620BFN, a 256-byte Capabilities Data Structure is embedded in the design and FW should initialize the content before setting EARC_HPD bit to '1'. The read/write access in IT6620BFN is accomplished by internal FSM and the FW just need to take care the ERX_LATENCY update when detecting the ERX_LATENCY_REQ is written by eARC TX.
In order to backward compatible with the ARC mode, the IT6620BFN also provides a complete solution of Consumer Electronics Control (CEC) function. This optional CEC feature of HDMI specification allows users to control two or more CEC-enabled devices through HDMI network. With this embedded CEC PHY, users can use high-level software API to easily implement all the necessary remote control commands. The CEC bus related protocol is handled by the CEC PHY, which eliminates extra loading of the MCU.
