Had an opportunity to upgrade my HTPC, picked up a 5700G put it in a B550 board and grabbed 2x8GB 4000 17-17-17 memory cheap. Trouble is, with XMP and Gear Down mode enabled, it's running 18-17-17 at 1T, if I disable Gear Down it runs 17-17-17 at 2T which performs worse. If I force 17-17-17 and 1T it's a no-POST.
It's at 1.35v, do I just need to feed it more voltage? Or does AMD just not like odd-numbered CAS Latency? Never had a problem with 3200 C14 or 3600 C16 running XMP.
1 Solution
From my troubleshooting it seems it's something about the odd-numbered CAS Latency.
I tried leaving XMP and Gear Down enabled and force CAS 17 in the BIOS and it would still boot using CAS 18.
So I bumped the voltage to 1.4v and forced 16-16-16-36 leaving XMP and Gear Down enabled and all else on Auto and I'm satisfied with the results:
From my troubleshooting it seems it's something about the odd-numbered CAS Latency.
I tried leaving XMP and Gear Down enabled and force CAS 17 in the BIOS and it would still boot using CAS 18.
So I bumped the voltage to 1.4v and forced 16-16-16-36 leaving XMP and Gear Down enabled and all else on Auto and I'm satisfied with the results:
Gear down mode de-syncs true memory speed with the IMC speed, so I believe that the fact your system is not getting along with Gear Down mode OFF 1T could be because of the CPU IMC not able to get stable at 2000mhz. (DDR 4000MT)
Normally, you can get around this with a small bump in vSoC, VDD/VDDQ voltages or increasing timing latency, whichever produces the best results. But Gear Down Mode always produces much better stability results, for obvious reasons.
Then stress test it. However, in theory, GDM OFF and 1T/2T should produce better gaming results, but that's not always the case in every game. In fact, its all over the place.
Or, downclock it to 3600Mhz and tighten REAL UP the latency timings, sometimes its better this way as 3600 seems to be the sweet spot of that generation. (I think...)
I would agree @johnnyenglish and do use DDR4-3600 with my Vermeers (5600, 5700X) as the IMC and Fabric usually top out around 1900MHz anyway, even with increased voltage.
However the 5700G is a Cezanne, it is a monolithic die it does not use the same I/O chiplet as Vermeer, and the IMC/Fabric of Cezanne is capable of much higher clocks in Coupled mode. I was being somewhat conservative using 4000 memory, with increased SoC voltage most of these can hit 4400 1:1:1 however low latency 4400 is pricey even used and typically requires 1.5V or more. This is my HTPC, it's primarily for streaming and occasional light gaming.
GDM disabled with 2T performed worse for me but it was close, as the results you shared also indicate, the differences are slight. I am using the IGP with the system memory so it may impact graphics performance differently. With GDM enabled CPU-Z and Ryzen Master both indicate using 1T but I have seen it described more as "1.5T" and as you say it helps with stability.
The UMA Frame Buffer defaults to 512MB so I increased that to 2GB. Coupled with the memory bump I also tweaked PBO settings (90 PPT, 60 TDC, 90 EDC, +200 CPU and GPU boost, -25 CO on CPU and GPU) and get 4850MHz single / 4700MHz all-core and 2200MHz GPU with all else on Auto.
https://www.techpowerup.com/gpuz/details/ahskq
