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  3. AR# 47580: Zynq-7000 SoC, DDR - LPDDR2 Per-Bank Refresh Is Not Supported

AR# 47580

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Zynq-7000 SoC, DDR - LPDDR2 Per-Bank Refresh Is Not Supported

Description

The LPDDR2 per-bank refresh function is not supported.

Solution

Impact:

Minor.

Work-arounds:

The work-arounds are explained below.

Configurations Affected:

Systems that use the DDR memory controller in LPDDR2 mode with eight banks.

Device Revision(s) Affected: All. No plan to fix. Refer to (Xilinx Answer 47916) - Zynq-7000 SoC Silicon Revision Differences.

 

The best overall work-around is to avoid using per-bank refresh, and to use all-bank refresh instead (i.e., set reg_ddrc_per_bank_refresh = 0).

If this is not acceptable, the individual issues can be worked around as follows:

  • For the duration of initialization, set reg_ddrc_t_rfc_min to the value appropriate for all-bank refreshes. When initialization is complete (detected by monitoring ddrc_reg_operating_mode), this can be changed to the value appropriate for per-bank refreshes.
  • Avoid high priority activates by programming the CAM to be a single priority. This can be done by setting reg_ddrc_lpr_num_entries to 31.
  • Avoid accessing mode registers when auto-refresh is enabled reg_ddrc_dis_auto_refresh must be set to 1 when performing MRW or MRR. Also, automatic temperature derating must be disabled in order to prevent automatic MRRs from being executed; reg_ddrc_derate_enable must be set to 0.

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
47916 Zynq-7000 AP SoC Devices - Silicon Revision Differences N/A N/A
AR# 47580
Date 05/25/2018
Status Active
Type Design Advisory
Devices
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