On our custom iMX6 ULL design the DDR calibration fails while the DDR stress test 3.0.0 is running without any problems (964 iterations so for) also when the DRAM frequency is set to 450MHz.
DDR Stress Test (3.0.0)
results from DDR Stress Test tool:
Start write leveling calibration...
running Write level HW calibration
MPWLHWERR register read out for factory diagnostics:
MPWLHWERR PHY0 = 0x00000000
HW WL cal status: no suitable delay value found for byte 0
HW WL cal status: no suitable delay value found for byte 1
Write leveling calibration completed but failed, the following results were found:
MMDC_MPWLDECTRL0 ch0 (0x021b080c) = 0x001F001F
Write DQS delay result:
Write DQS0 delay: 31/256 CK
Write DQS1 delay: 31/256 CK
Error: failed during write leveling calibration
I tried calibration both at 400 and 396Mhz but still failing.
I also tried version 2.6.0 of the ddr_stress_tester tool and with this version the Write level HW calibration passes (and also the remaining calibration)
no problems are seen when running the memory test of the ddr_stress_tester (without doing the calibration)