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USB Audio DAC PCM2707 SPI issue to program device descriptor

Matt55124
Prodigy 45 points

Hi,

I use a PCM2707 in my design, with the SPI i'm able to send command like Play/Pause Next Previous so I think the hardware is OK.

 

I want to use the SPI to program the device descriptor to configure the Product and Vendor strings

I want to precise this is not a trouble of D+ pull up I desactivate it during the device descriptor programming.

I have noted the data should be sent from LSB to MSB and also they should be sent continuously after the ADDR bit has been set to 1.

I think this maybe coming of timing issue.

If we look to the page 24 of the datasheet I should be in the case continuous write operation to send the 456 bits of ROM

My question should I have a delay between each 16 Bits?

 

Do you see others explanations? or any advice ?

 

Thanks in advance

 

Best regards,

 

Matthieu

  • 0
    Prodigy 75 points

    Hi Matt,

    did you have any success with the descriptor programming?

    Greetings

  • 0 in reply to t0mmy
    Prodigy 45 points

    Hi,

    Hopefully I succeded it was almost 7 month ago.

     

    Cheers,

    Matt

  • 0 in reply to Matt55124
    Prodigy 240 points

    Hi Matt,

    TI's documentation around this subject is very poor and possible missleading (?) and I have tried all possible alternatives that I can come up with when writing this data. Where is the error?


    How did you mange to get the right data into PCM2707 over SPI?

    best regards,

    Esa

  • 0 in reply to Esa Harma
    Prodigy 240 points

    Ok.


    I just realized that the biggest problem may be how to produce the needed continuous flow of 16bit X N Frames with an SPI hardware that has byte oriented data!!!

    Esa

  • 0 in reply to Esa Harma
    TI__Mastermind 27850 points

    From the datasheet what I understand is that the following is needed for programming the descriptor over SPI:

    • PSEL = High
    • HOST Pin = High
    • D+ pull up not activated
    • LSB first (within the 16 bit word) with specified byte order

    To start the Descriptor write, a 16 bit word setup as followed must be sent to the part:

    Where for the first word will be, ST = 0 and ADDR = 1, and D0-D7 will be an HID status. Then the next 57 words will be sent continuously, following the timing diagram on page 24 of the datasheet with ST=1 and ADDR = 0 and D0-D7 being the descriptor data. 

    Is this how it is currently being implemented?

    Justin

     

  • 0 in reply to Justin Bohr
    Prodigy 240 points

    Hi Justin,

    No, this is not how we have tried to do the descriptor write since present PCM2707 documentation tells that after reseting the ROM address counter by writing ADDR=1,  "456 bits of ROM data must be continuously followed after this bit has been asserted. The data bits must be sent from LSB (D0) to MSB (D7)".

    456 bits = 57 bytes and not words.

    My interpretation about you email is follows:

    1. Reset ROM address counter by by writing hex data "0x02 XY" i.e. ADDR=1 and XY is actually a dummy HID write (USB DAC has not yet even been enumerated by the PC since D+ pull-up has not been activated).

                            Question: Is this really necessary? We have just booted up. Reset the counter just to be sure?

    2. Write the 57 bytes of data in 57 words as "0x04 DB" where ST=1 and ADDR=0 and DBs are the data bytes bits in D0-D7 order.

    Is this what you are saying?


    Esa

    PS. Real HID writes are carried out with D+ pull-up activated? If you deactivate the pull-up, your DAC will be disconneted for a while, doesn't it? And this is not a good idea in my opinion.

  • 0 in reply to Esa Harma
    TI__Mastermind 27850 points

    Hi Esa,

    Yes this was not presented in the clearest way in the data sheet, but looking and the timing diagram it shows that a continuous write is 16 bits x N frames, which would be 57 words, carrying 8 bits of ROM data each, with ST =1 and ADDR = 0 to get the 456 ROM bits. Your interpretation is the scenario I believe will work.

    As regards to the D+ pullup I am not sure about the operation of that with the DAC and will have to look more into it.

    Justin

  • 0 in reply to Justin Bohr
    Prodigy 240 points

    Hi Justin,

    the descriptor can be written using conventional 8-bit SPI data in 114 bytes with every odd byte as 0x08 and every even byte as the 8-bit descriptor data in D0 ... D7 order, as you described.

    It seems that reseting the counter is actually not needed.


    Thank you for your help.

    Esa