I have an ADAU1446 on a board that was working on the last spin of the board, but on this board spin, none of my boards are able to communicate to SigmaStudio through the USBi dongle. I have done two other designs with the ADAU1446 and never had problems talking to it over I2C. My DSP is basically a brick, as it refuses to respond so I can program it.
I'm driving the chip with an external oscillator, so I don't even have the presence of an oscillating crystal to tell me whether the DSP is a brick or is running. The only thing that tells me that at least a tiny bit of the DSP is working, is that on all my boards, DVDD is right at 1.76V. Since DVDD is generated by the DSP itself with the PNP transistor, this proves at least part of the chip is working and is oriented correctly on the pads.
I only have I2C hooked up to the chip, and I'm wondering if perhaps the chip is trying to be in SPI mode. Perhaps I have a non-connected pin that is floating such that it goes into SPI mode. Is this possible? How do I guarantee the ADAU1446 is in I2C mode?
I have looked at the oscillator input into the DSP, and it looks OK. It's a 12MHz signal with no jitter visible on the scope. The I2C signals from the USBi look normal on the scope, I have two EEPROMS and two CODECs on the I2C bus, as well as the DSP. I can use the USBi and SigmaStudio to write and read the EEPROM. No CODECs or EEPROMS are at 0x70, which is where the DSP should be, as both of it's address lines are tied low.
 Schematic of DSP Attached
 Oscillator waveform into XTALI