We have a collection of ten Vybrid-based cards with DDR3 (Micron MT41K256M16HA-125 AIT:E). Based on the TWR-VF610 we have configured the DRAM and successfully managed to run our application in the external memory. At boot time, we have some light-wight memory tests that run from the internal memory before the bootloader relocates itself to the external memory.
Out of these ten cards, two of these cards fail to boot when power is initially turned on. At this time, the boot-time memory tests indicate failure and the bootloader fail to relocate to DRAM, and instead crashes. However, if we then reset the card through an external watchdog, the card boot successfully, and the memory tests pass.
When either of these cards succeed to boot, the top-level application do run flawlessly and any memory tests we run succeed without failure.
We tried to implement a workaround where the cards would soft-reset if either of the internal memory tests failed. This seemed to help on of the effected cards, but not the other. The card would enter a reset-loop, which could only be aborted by hitting the reset-button.
Does anyone have an idea of what might be causing this issue? All boards mentioned are seemingly identical, and should in theory behave identical too. However this is not the case.