Can't set my CL15 RAM to CL15, but can set it to CL14

[Vexr]

I finally got around to setting up my RAM at it's advertised timings instead of just leaving it in XMP mode (which put it at 2933 MHz and CL16 with a couple of other timings being off).

The other timings set correctly, but after setting tCL to 15 and rebooting, it remained at CL16. I confirmed this in the BIOS itself, on CPU-Z, and SiSoftSandra.



I then set it to CL14, and this set correctly according to the BIOS and CPU-Z.



So I tried CL15 once more, and it again went to CL16 instead.

I haven't tested the new settings much, though I get a 1.5% increased CPU score in 3DMark at 3000 MHz + CL16 over the XMP settings. Apparently I only get a 0.1% increase in CPU score at 3000 MHz + CL14, though that could be a blip.

Anyone know what's going on here with all this? I've set it back to CL16 3 GHz for now.

 

[G550]

Disable Gear-Down mode in your BIOS if it's visible. From what I can remember, if an odd CAS latency is set, all Ryzen processors automatically drop down to the next even CAS latency setting if Gear-Down is active/enabled.

In my own experience with the Prime X470 Pro and Teamgroup B-die, the system will boot/run CL15 at up to 2666MHz or so, but beyond that it usually fails to boot or is unstable, regardless of memory voltage or timings.
Conversely, given enough memory voltage (eg 1.425V), CL14 runs fine at 3466MHz. I always stuck with CL16 at that speed, since the voltage requirement for stability was so much lower (1.32V).

Odd latencies just don't seem to work well with my setup. Maybe I missed something in the timings when testing, but not really worth bothering with in my case given CL14 is always there should I feel I ever really need it.

 

[Vexr]

Perfect, many thanks @G550 . I found a Gear-Down option, which I set from auto to disabled and it's now running at CAS 15.

Fortunately everything seems to work fine at this odd latency for me having put it through a few gaming benchmarks and 3DMark, though I haven't ran a proper RAM test as yet.