Am 26.09.2017 um 12:41 schrieb Michael Mrozek EvilDragon@openpandora.org:
Hi,
I've talked to the memory distributor about our recent discoveries (DLL off, etc.) and got the following reply.
I hope my translation is correct (as the original was in German):
DLL Off only affects Reading. Dual Die Input cap is more critical regarding writing.
DLL Off means that the data will not be sent based on the clock...
Does the controller do an auto-training during power up or are you using fixed timing values?
With DLL off you should have a lot more issues than with DLL On... I've got no real explanation why a Dual Die should work better with DLL Off than on (except for if the timings aren't properly setup / trained).
A possibility could be that the termination is improperly for the Dual Die. A proper simulation with IBIS can only be done if the ODT Timings and values are known.
But if hardware leveling doesn't work with high temperatures, then it's probably more than just a bit of tuning...
But if DLL off works better than DLL on, it certainly looks like a timing issue, not a termination issue. I can run a simulation, but I'd need to know the timing which are being used to, for example, enable the ODT or the Receiver.
It's a fact that a dual die has a higher I/O capacitance. Swinging high and low will be reducing between the signal flanks.
Is there a reference design with two ranks (can also be two ranks with monolithic ICs) where one could grab the value of the termination resistors and capacitors around the chips?
Two interesting things here: ODT Timings (they seem to be different depending on the chip used, have we checked those?)
And Termination. That's probably a question for Nikolaus: What resistors do we have here - and could those easily be changed for testing on a CPU board?
Quick answer: they are inside the DDR3-Chips and the OMAP5. Not explicit components that we do design choose or install. Should IMHO be possible to program them by software in some range.
There are in total 8 external resistors with 240 Ohm at ZQ0 and ZQ1. Appears to be one for every chip (4 packages of 2 chips each).
Maybe this value must be changed? I don't know what they are really good for... The data sheet only references these 240 Ohm:
• Driver strength : RZQ/7, RZQ/6 (RZQ = 240 Ω)
or
• Internal(self) calibration : Internal self calibration through ZQ pin (RZQ : 240 ohm ± 1%)
BR, Nikolaus