DDR3 access problems
Accessing the DDR3 with the same core as used on the SPEC card doesn't
work. After several correct write and read cycles, the DDR3 returns all
F as data, likely caused by an unexpected recalibration cycle initiated
for unknown reasons.
Causes can be various (missing calibration resistor, unequal length A/D lines, reflections, problems with Vref after starting up).
Needs debugging before design of V2.