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ADV7842 I2S output with compressed audio input

Question asked by DG1 on Jun 15, 2012
Latest reply on Jun 19, 2012 by DG1

This is an open letter to the ADV7842 design team.

 

I was not able to get any output on AP1 in the I2S format with a compressed audio signal (Dolby Digital) coming in over HDMI. Every status indicator showed that it should be working and that audio was unmuted. I tried playing with I2SOUTMODE and finally found some activity on the pin when I set it to RAW SPDIF. But the SPDIF signal didn't look right so I set it back to I2S mode and just for the heck of it I tried setting bit 7 of the register (HDMI Map 0x03). Lo and behold I got the correct I2S output!

 

Bit 7 in this register is not documented in the HW reference manual or the register map. This register is not written to in any of the HDMI scripts. Needless to say I am really pissed off about the lack of documentation, having wasted several days trying to get it to work. This is such a basic operation for this part, most cable channels use Dolby Digital for their audio, that I can't believe this wouldn't have been tested and documented properly.

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