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Thread: XMC4800 Ethernet DMA descriptor selection

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    New Member New Member Fredrik Möller is on a distinguished road
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    XMC4800 Ethernet DMA descriptor selection

    The reference manual chapter 15.2.4.1 describes three kinds of DMA descriptors:
    * Normal descriptors (16 bytes)
    * Alternate descriptors (16 bytes)
    * Enhanced descriptors (32 bytes)

    Question 1:
    What is the default descriptor selection?

    Question 2:
    How do configure the hardware to use Normal or Alternate (16 bytes) descriptors?


    I'm developing a driver for the Ethernet MAC, i.e. not using DAVE/xmc_eth_mac.c.

  2. #2

    Infineon Employee
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    jferreira will become famous soon enough
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    Hi,

    The default after reset is normal descriptor format.
    You can change it using the code below
    Code:
     
    /* Increase enhanced descriptor to 8 WORDS, required when the Advanced Time-Stamp feature or Full IPC Offload Engine is enabled */
      eth_mac->regs->BUS_MODE |= (uint32_t)ETH_BUS_MODE_ATDS_Msk;
    What is the reason for you to write your own low level driver? Are you missing any functionality? Your feedback is appreciated, we are always open to incorporate user proposals.

    Best regards,
    Jesus
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

  3. #3
    New Member New Member Fredrik Möller is on a distinguished road
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    Thanks for your answer!

    Isn't it true though that setting ETH_BUS_MODE_ATDS will always expand descriptor size to 32 bytes (instead of 16 bytes)? What I really want is to use the 16 bytes Alternate descriptor layout.

    I'm not writing the driver from scratch, but rather reusing an existing one written for another hardware platform (not Infineon). The other platform uses a version of the same Ethernet IP block.

    Best regards,
    Fredrik

  4. #4
    New Member New Member Fredrik Möller is on a distinguished road
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    I tested with the Normal DMA descriptor layout, but that didn't work. Changing to Alternate 16-bytes layout worked. It appears as the Alternate 16-bytes descriptors are the default. The reference manual should be updated to reflect that.

    Also, if Normal descriptors are not implemented in hardware, as it seems to be the case, then the section in the reference manual covering Normal descriptor should be removed.

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