CROSSHAIR 8 X570 : Quest for a perfect Base Clock of 100 MHz

[contact1]

Hello,

I'm measuring the BCLK of the Ryzen 3950X using its Core TSC
( an algorithm of two instructions RDTSCP elapsed by one second )

Results are 99.8 MHz on any Core, which is lower than the Processor factory 100 MHz.

After refining my TSC measurements by removing the inherent cycles of RDTSCP, setting the P-State to a fixed ratio, and all possible programming improvements; I'm still getting a estimated Base Clock of 99.8 MHz.

Thus I have questioned the BIOS and I went into the UEFI settings to change the BCLK from 100 to 100.0625 MHz (the first step above 100) ; save, reboot, and measure the TSC to get a coherent frequency of Cores at ~ 3502.2 MHz (35 * 100.0625)

Next, I changed back into UEFI the BCLK from 100.0625 to 100.0 MHz ; save and went straight into measurements to get an almost perfect Cores frequency of 3500 MHz

Unfortunately, the following boots restored the BCLK to an estimation of 99.8 MHz

Question is how to manage the BIOS to retain the willing Base Clock of 100 MHz ?

[contact1]

Disabling SPREAD SPECTRUM has solved the issue. I did it on VRM and SB and now my BCLK perfectly reports 99.9 - 100 MHz



CoreFreq monitoring at github.com/cyring/CoreFreq