Comment by nsteel

Implementing DDR3 training for our packet queuing chip (custom memory controller) was my first project at work. We had originally hoped to use the same training params for all parts. That wasn't reliable even over a small number of testing systems in the chamber. DDR3 RAM parts were super cheap compared to what we had used in previous generations, and you get what you pay for with a huge amount of device variation. So we implemented a relatively long training process to be run on each device during our board testing, and saved those per-lane skews. But we found the effects of temperature, and particularly system noise, were too great once the system was sending full-rate traffic. (The training had to be done one interface at a time, with pedestrian data-rates). We then ended up with a quick re-training pass to re-center the eyes. It still wasn't perfect - slower ram chips (with smaller eyes) would report ECC correctables when all interfaces were doing worst-case patterns at temperature extremes. We spent a lot of time making those interfaces robust, and ended up relying more on ECC than we had intended. But those chips have been shipping ever since and will have seen traffic from most of us.