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Questions schematic design: I2C EEPROM and WM8804

Former Member

Hi All,

I have a question about the schematics of the Cirus Logic Audio Card.

 

I just compared the schematics of the Cirrus Logic / Wolfson for use with the RPi A+ B+ (from now on i call it the new one) with the older Wolfson RPi A Audio Card (from now one i call it the old one). I have noticed that the new one has a EEPROM I2C memory on-board (U10). I was wondering what the purpose of that memory chip is. The chip is configured as write protected (pin 7 = pulled up).

 

Also, I see that the I2C bus is connected to the WM5102 via the 0 ohm resistors and the WM8804 SPDIF Transceiver.  I can see why the I2C bus is connected to the WM5102, so one can experiment with the I2C communication capabilities of the WM5102 (hence the 0 ohm resistors and the header J2 which is pulling the I2C out after the resistors). But the WM8804 could in my opinion run run autonomously (with a hard wired configuration setting).

While I'm writing this, I realize that my real question is: where can i find some good documentation on the driver. Some more technical docs on the design of the hard and software.

 

I've ordered a Cirrus audio card which will be delivered tomorrow, so then it is possible for me to do some measurements on the I2C busses and other things, to see whats going on.

 

I really appreciate all your help,

 

Jeff

  • Hi Jeff,

     

    The EEPROM serves an only semi-useful purpose but isn't essential. It basically is intended to contain information which the Pi can read, to determine at boot what the card is, and to configure ports and drivers accordingly. With something as generic as a sound card it possibly doesn't need to do much card-specific configuration but I've not checked the schematics in detail. Even without the EEPROM there is nothing stopping a user from configuring the Pi to use the card, its just that the configuration won't be as dynamic (if say the card is unplugged and replaced with a different one). The EEPROM is part of the Pi's 'HAT' card specification (this concept can also be seen on the BeagleBone Black). With an embedded system you'll usually know what cards are plugged in so this is less essential.

    I don't believe there is any additional published official documentation on the software or hardware, beyond the driver code, schematic, and the device datasheets which should provide good information to help understand the hardware.

    The schematic is here: Cirrus Logic Audio Card for B+ and A+ Onwards Schematics