IT6621: ARC/eARC Transmitter
The IT6621 is a transmitter designed for HDMI 2.1 Enhanced Audio Return Channel (eARC) and it is also backward compatible with 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 IT6621 adopts eight I2S and one SPDIF signals for the audio input interface. Eight I2S signals are used to transmit multi-channel L-PCM audio and the maximum 16-channel audio is supported by the IT6621. 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. In IT6621, the MCLK is necessary when SPDIF interface is selected. 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 IT6621.
For the compress audio, 8-bit ECC syndrome is added to 16-bit audio data by HW in the IT6621 and 1-bit error in compress audio data could be corrected by HW in the eARC RX. To increase the security of the eARC audio transmission, HW encryption mechanism is also implemented in the IT6621. Because the content protection method is not a standard in eARC specification, FW of IT6621 must make sure the eARC RX is IT6620 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 IT6621 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 IT6621, CMDC read/write command is triggered by FW through high-level I2C interface and the HeartBeat is triggered by HW itself without any FW efforts.
In order to backward compatible with the ARC mode, the IT6621 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.
