I have two i.MX6 boards, with a total of 2GB DDR3 SDRAM (4 x 4GBit), 64-bit bus. I used the DDR Stress Tool V2.51 to calibrate the DDR, running from an SD card, using the following commands in u-boot:
u-boot> dcache off
u-boot> icache off
u-boot> fatload mmc 1:1 0x00907000 ddr-test-uboot-jtag-mx6ul.bin
u-boot> go 0x00907000
For Board #1, the calibration always succeeds. For Board #2, the calibration sometimes fails (~one time of out ten) on:
DDR Calibration failed during Read calibration:
The result is 0x11111111 for the entire run of DDR Calibration failed during Read calibration.
Using the average calibrations from Board #1 and Board #2 (for the successful calibrations), both boards pass the DDR stress test, which was run for 3 hours. Any idea why Board #2 sometimes fails calibration?