X370 Taichi - trouble with RAM settings

Hi. I have been running with the default (all Auto) settings for my RAM since I built my Ryzen computer (specifications below), which feels like a waste. I had not tried increasing the RAM speed until now because I have had some problems :

- I used to have a faulty CPU (segfault bug), but AMD exchanged it for me and the new 1700X I got seems to work fine.
- My system will sometimes completely freeze unless I use the following option : Advanced > AMD CBS > Zen Common Options > Power Supply Idle Control > Typical Current Idle. I know about the freezes that people are having on Linux (still now), but this happens both on Windows and Linux for me, so it might not be exactly the same thing.

Complete system specifications :

Case: Thermaltake Suppressor F31 (with Noctua fans instead of those that came with it)
PSU: Corsair RM650x
Mainboard: ASRock X370 Taichi, BIOS 4.70.
CPU: AMD Ryzen 7 1700X + Noctua NH-U12S SE-AM4
Memory: G.Skill Trident Z 32 GiB F4-3200C14D-32GTZKW
Graphics card: Zotac GeForce GTX 1070 AMP!
Storage: Seagate Barracuda 2 To
DVD drive: ASUS DRW-24D5MT


So, I think that it would be nice to run the RAM at 1333 MHz instead of the default 1066 (as a compromise since 1600 most likely wouldn't work). Yesterday, I used the Ryzen DRAM calculator and I got the safe values for a speed of 2666 MHz (DDR).

But I am not able to get those settings exactly in the BIOS. If I load the XMP profile and change the DDR frequency to 2666 MHz, then the computer boots with that frequency, but it keeps the XMP timings and voltage (1.35 V). (The timings computed by the Ryzen Calculator tool for 2666 MHz are, as expected, lower than the XMP profile timings.)

After that, I tried not enabling the XMP profile (leave the setting on "Auto"), and setting the RAM frequency in Advanced > AMD CBS > UMC Common Options > DDR4 Common Options, but it did not work because the BIOS didn't keep this setting, and it reverted to "Auto".

I then tried different combinations :
- with the "OC Mode Change Switch" setting on "ASRock setting" or "AMD CBS"
- enable or disable "AM4 Advanced Boot Training". It should be disabled anyway since I want to manually enter values, shouldn't it?

But nothing seems to allow me to get at the same time the desired timings, frequency (1333 MHz) and voltage recommended by the tool (1.33 V). The 1333 MHz frequency seems to stick only when I disable the memory training, but then the DRAM voltage is always shown to be 1.352 V in HW Monitor (sometimes 1.344 at first, but only for a very short while, it seems.) and the timings that are applied are those of the XMP profile, even though I don't enable it... The memory frequency always reverts to the default 1066 MHz in any other case I have tested, and the voltage is always 1.35 V, although the BIOS setting still shows the 1.330 V I have set !

As for the SOC voltage, Ryzen Calculator recommends 1.025 V. This setting works (I can see something like 1.024 or 1.032 in HW Monitor). I've also noticed that if I leave the default voltages and 1066 MHz DRAM frequency and I only set the lower timings given by Ryzen Calculator, the system boots normally. But I don't think that it would always be stable like this

This is very confusing. Am I doing something wrong? Is the BIOS bugged?

I am using v4.70 for the BIOS because older 3.x versions don't have the "Power Supply Idle Control" setting, hence my system would sometimes freezes, and when I upgraded the BIOS, v4.70 was the latest one. I don't think that those older versions have the security fixes for Spectre either, so I would prefer not to downgrade. On the other hand, I was told that the 5.x versions don't have "Power Supply Idle Control" anymore !

Another thing I was told by someone who also used to have freezes with the X370 Taichi is that the default SOC voltage is too low. So just raising the SOC voltage might be a fix, and then I would no longer need the "Power Supply Idle Control" setting.

Thank you for any advice