3.4.2 Programming requirements for designs with an alternative path to the HN-I memory space

For slaves that are in the HN-I memory region, some system designs might provide access to those slaves through a different path from the HN-I. In these circumstances, you must program the HN-I registers so that the Point-of-Serialization (PoS) is set correctly.

The following figure shows an example system configuration where an HN-I slave is accessible to other AXI masters.

Figure 3-147 HN-I slave that is accessible by other masters
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The required programming is:

  1. Set hni_pos_en = 0 in the HN-I pos_control register, so that the HN-I is not the final PoS.
  2. Optional: Set honor_ewa_en = 1 in the HN-I sa_aux_ctl register.
    This bit controls whether the HN-I passes downstream error responses for writes.
  3. Set the four pos_* bits to zero in the HN-I sa_aux_ctl register.

    That is, set:

    • pos_early_eobarrsp_en = 0.
    • pos_early_rdack_en = 0.
    • pos_early_wr_comp_en = 0.
    • pos_terminate_barriers = 0.
  4. Set ser_devne_wr = 1 in the HN-I sa_aux_ctl register.
    When set, the HN-I serializes the Device-nGnRnE writes, and does not send any other write request with the same AWID as an outstanding Device-nGnRnE write.
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