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ROG Crosshair VIII Hero / Formula / IMPACT / DARK HERO LN2 OC Guide

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1. Update AGESA version to ComboV2PI 1202.

Before running the USB BIOS Flashback tool, please rename the BIOS file (C8I.CAP) using


HERO : https://drive.google.com/file/d/1BvIlw4q5jY8h6BqeIhXbYsYIIE3AwBbb/view?usp=sharing

HERO WIFI https://drive.google.com/file/d/1rMxwt6cceG9aV7ykz5vMlLvtRkvfbYT5/view?usp=sharing

FORMULA : https://drive.google.com/file/d/1y9jQSwA8kewYkTwCYqHvuASWsxEf3KUS/view?usp=sharing

IMPACT : https://drive.google.com/file/d/1aDTFn5FfO9gUBrZlLaz96pxO6Rl2suYC/view?usp=sharing

DARK HERO : https://drive.google.com/file/d/1T6rPm9vHn8UUkUF2PuVkqoHufpu7cw5f/view?usp=sharing



TURBOV : https://bit.ly/3895WBz

OCTOOL : https://tinyurl.com/y3hu2hg3


tRFC / tRFC2 / tRFC4 now max value can do 1023.
LN2 jumper enabled, FCLK = 1566, VDDG CCD = 1.2V, VDDG IOD = 0.9V.
LN2 jumper enabled DRAM voltage = 1.65V.



Turbov and CCX OC Tools : https://bit.ly/2MHzo7X

MemTweakIt : https://bit.ly/2UhX8An

Zen Perfboost : https://bit.ly/2kBs15c (After loading CineBench R15 or Geekbench3 bench then run the boost, just click defaults button after benching to prevent bsod)


USB Flashback





There is an FCLK cold bug under LN2 so try to stay around 1400~1600 for FCLK under LN2 to get a good compromise between temps and perf.

To improve stability in this case:

VDDG 1.15v, SOC 1.28v, disable DF Cstates.

Depending on the CPU and FCLK, may have to control temps -120C ~ -170C.

I typically use 1.35v ~ 1.55v SOC just to get as high an FCLK/Cold bug margin as possible.


Do not be alarmed when it resets when temperature changes, pcie and fclk needs to retrain when temps change. Also sometimes there is temperature hole so going lower than it hangs may help.


Biggest problem on the platform

1200 default freq and supposed to go 1:1 with memory for best latency.
Improves performance but limited, ~ 1800+ on air and 1400 on LN2.
FCLK instability includes hang at postcodes such as ‘07’, stuttering in OS, drop performance in Cinebench.
CPU has FCLK cold bug.
Improve FCLK Margin by using 1.15VDDG (too much will hang) and 1.3+v SOC. Since VDDG is sourced from SOC so SOC should be higher. VDDG only takes effect at 1400+ FCLK so under LN2 you need to set 1400. Higher usually fails during LN2.

Enable LN2 mode, Use the Load LN2 profile as a base template, this uses low vcore so you can save exit when it’s not cold. You will need to do this before -40C to avoid cold bug. You need 1400 FCLK + 1.15v VDDG and 1.35~1.45VSOC.


Post codes

07 too high fabric / fabric unstable (can press reset 2~3 try but If not solved You need to reset the flck clock after lowering the temperature to -120c.)

F9 or 23 : High Memory Clock / Tight Timings (Memory reset need)

other code : (can press reset 2~3 try but If not solved You need to lower the temperature to 100c ~ 120c.)


About AMD Limitations

Safemode cannot restore back to stock memory settings as this takes place in the ‘PSP’ which the BIOS has no control over at that point of time. Either you have to clear cmos or wait for 5 times of post code ‘F9’ to get into AMD’s recovery mode. AMD’s recovery mode restores every AMD option back to stock, including timings and CLDO voltages.

Because of the above, try not to clear cmos during LN2, at most go safe mode if your settings can be sustained with 1.5v DRAM, since BIOS will apply 1.5v for safemode when LN2 enable. IF you clear cmos, FCLK will go back to Auto and CLDO VDDG voltage will too. When cold, FCLK needs to be 1400+ and VDDG 1.15v if not Fabric will be unstable so you need to torch up to maybe -60c in this case. Therefore test your Memory settings on ambient first. Cold CPU improves Memory OC so you don’t need to worry about MC cold bug.













Edited by safedisk
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BIOS UPDATE 2021/04/22 UPDATE ROG CROSSHAIR VIII HERO / FORMULA / IMPACT / DARK HERO 3501 BIOS 1. Update AGESA version to ComboV2PI 1202. Before running the USB BIOS Flashback tool, ple

https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/ROG_CROSSHAIR_VIII_IMPACT/ROG-CROSSHAIR-VIII-IMPACT-ASUS-3003.ZIP   Version 3003 2020/12/07 20.13 MBytes ROG CROSSHAIR VIII IMPACT BIOS 3

I tested 0050 bios. no cb. Very good for me nice bios.  If you stop at -150 to -180 temp code cc, press reset button 2~5 try.  

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GEEK3 and Hwbot 4k tip


The fclk clock is very important for the above two benchmarks.

must change the fclk clock and the cpu clock to find the highest clock value that can be run.

fclk The higher the clock, the lower the cb temperature.


good luck




Edited by safedisk
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C8I 0050 BIOS agesa


Fix Incorrect MemClkFreq above DDR-5000.
Add micron/spectek DDR4-5000 auto tuning rule.
Add SK Hynix DJR DDR4-5000 memory preset.
Add memory OC fail count, 0 is disabled will not recovery setting and enter safe mode, max 10-times retry.
Add BCLK fraction function.

No cb


Edited by Alex@ro
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Haha, happy to see that it helped you ;)

  • For french guy you have all setting in this video  * here * :
  • For "other" you can still look at this it but without audio 😛

You can try Cas14 or more MHz also but was not booting for me. This is 1 CCD CPU, with 2CDD you will have better result. Tight SUB et TER as much as possible, I ran out of time so there is probably headroom to improve it.

I also did a 7h long stream for XOC, video should be export soon.


BTW, I have really strange behaviour with my 3600x and IMPACT (0050), :

  • If I boot between 20 and -68 I have a CB at -69°C and MB shut down
  • If I try to boot OR re-boot from -70 to -170 I have "d6" code and no display

So the ONLY way I find is to boot and re-boot EVERY TIME at -69°C, not -68 neither -70 but -69... is really boring.

I tried :

  • FCLK from 1200 to 1600 but no change on CBB (only on CB)
  • VDDG from 1.15 to 1.2
  • CPU ratio / voltage
  • Stock mem or 4800c15 mem
  • LN2 mod and LN2 profil
  • ...

Safedisk & Alex@ro did you got same problem  ? Any idea ?



Edited by Wizerty
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  • safedisk changed the title to ROG Crosshair VIII Hero / Formula / IMPACT / DARK HERO LN2 OC Guide

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