What to try next in debugging bringing up an I2S audio codec?

General Electronics
1

Hello everyone! I found this post on the Wayback Machine about being unable to read NAU8810 registers: https://web.archive.org/web/20230212204134/https://www.reddit.com/r/AskElectronics/comments/110pon6/unable_to_read_registers_in_nau88c10_audio_codec/?utm_source=reddit&utm_medium=web2x&context=3

I am having the exact same issue! But it doesn’t look like anyone commented before the user deleted their post. I’m excerpting their description of the problem below, as I see the same symptoms:

The chip has a standard I2C control interface. When I run the I2C scanner sketch with it all wired up, I can see that it’s detecting an I2C device with address 0x1A, which is what I expect. But when I try to read any registers, I just get zeros back, except from 0x0C, 0x0D, 0x1C, 0x1D, 0x24, and 0x25, which read as 0x01. I have 4 other devices that I’m able to interact with on the I2C bus without a problem. Also, I am using 3.3V to power the digital logic of the NAU8810, and a 3V LDO to power the analog side of the NAU8810.

I also found this linux discussion of the regmap format of the codec, but I don’t know whether the 7x9 regmap discussion is relevant, since I am adapting this driver that seems to work with “normal” microcontroller I2C usage.

Here’s the schematic page that has the NAU8810 and supporting electronics: nau8810 schematic.pdf | DocDroid

At this point, I feel like I’ve run out of ideas for what to try next. I’d really appreciate suggestions of what else I could do. Thanks in advance for your help!

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This nice redditor pointed me in the right direction. I’m copying my comment here, to aide future searchers (and also, maybe it’s interesting if you’ve never dealt with 9 bit registers over I2C like me).

In order to read a register $r, you should do a 16 bit read operation from register $r<<1, because the LSB of the register should be 0/you should treat the register as a 7 bit value.

In order to write a 9 bit value $v to a register $r, you’re supposed to do an 8 bit write operation. The register address is then ($r<<1 | ($v>>8) & 1), and the data is ($v & 0xff). This takes the MSB of the data and shoves it into the LSB of the register address.

I’ve now got control of the NAU8810 :slight_smile:

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