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[DDR3, C6678] HW re-design required when changing from 64bitDDR3 to 32bitDDR3 ?

Naoki Kawada
Guru 19890 points

Hello,

One of my customer was designing C6678 target board with 64bit DDR3 (16bit DDR x4) by following design guides related to DDR3:

  • Hardware Design Guide for KeyStone I Devices
  • DDR3 Design Requirements for KeyStone Devices

But now they are considering to change 32bit DDR3 (16bit DDR x2) with minimal hardware change (almost same layout, connection, etc. just considering to disable upper side of DDR[32-63] and its control lines).

I believe DDR3 32bit would not work with the HW design for 64bit configuration, but they would like to have your comment on this. Any suggestion ?

Also, I have a question. If ECC feature is not required, I think DDRCB[7:0] should be floating. Correct, right ?    

Best Regards,
Naoki Kawada

  • 0
    TI__Mastermind 43660 points
    Hello Naoki,

    Yes, In general, a board with a 64-bit implementation can be configured for x32 operation. The total memory size will be halved. The NM bit should be the only change at the DDR3 interface configuration level.

    Please refer the below threads where similar queries have been addressed in detail.

    e2e.ti.com/.../382990

    e2e.ti.com/.../158933

    If you are not using ECC feature, you could leave the DDRCB[7:0] pins unconnected.

    Regards,
    Senthil
  • 0 in reply to Senthilkumar Srinivasan
    TI__Mastermind 46460 points

    Naoki-san,

    Yes, conversion from an x64 topology to an x32 topology is simply removal of the 3rd and 4th x16 SDRAM device.  Additionally, you can configure and run the board containing the x64 topology in x32 mode simply by changing the NM bit as stated by Senthil.

    Yes, the CB[7:0] pins can be left floating when ECC is not used.  Please refer to the referenced design guides related to DDR3 for a complete discussion on handling unused byte lanes:

      • Hardware Design Guide for KeyStone I Devices
      • DDR3 Design Requirements for KeyStone Devices

    Tom

     

  • 0 in reply to Tom Johnson 16214
    Guru 19890 points
    Hello Tom and Senthil,

    Thank you very much for your quick reply. OK I understood. We'll suggest the same to the customer.

    Best Regards,
    Naoki Kawada