SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
In HS200 Mode, the BIST engine in the PHY runs Tuning Pattern test 32 times, with different TAP values selected, for each iteration. The result from the 32 iterations is presented on the MMCSD0_SS_PHY_STAT_2_REG[31:0].BISTSTATUS output. It is expected that some of the TAP values will have timing issues and results in pattern mismatch when compared with the received pattern for those taps. The PASS/FAIL for the HS200 Mode is based on the following theory.
Of the 32 taps, the Data Capture EYE for certain taps will result in mismatches, but these will be sequential tap values. Thus, in a full 32 iterations, a sequence of taps results in data mismatches. Also, based on the timing closure, the number of taps with pattern mismatch should be approximately 1/4th of the number of taps with pattern match. This 1/4th count is not absolute, as this involves various factors such as the timing closure, PVT variation, and so forth. Anywhere from 4 to 16 invalid sequential taps is normal.
For example, if 8 of the 32 sequential taps have the data mismatches, the following would be the resulting MMCSD0_SS_PHY_STAT_2_REG[31:0].BISTSTATUS output based which of the 8 sequential taps the mismatches are. The following is the notation used: