How do you fine tune memory clocks?

[bhavvv]

Is this even possible? E.G. the board says it supports 3333 Mhz memory, but you can normally only select 3200 or 3400.

So how would I go about trying to clock the memory between 3200 and 3400?

Because I have 3200 stable with very tight timings, but 3400 wont boot, so I would like to try in between the two.

[Praz]

Hello

For a 3333MHz memory divider set the CPU Strap to 125MHz.

[Brighttail]

Switching the strap to 125MHz has a downside as it can cause the CPU to be unstable.

You could add a little to the ratio of the strap, maybe 101.0. That would take your 3200 to 3300 I believe.

[Raja]

Brighttail wrote:
Switching the strap to 125MHz has a downside as it can cause the CPU to be unstable.

Assuming all else is equal, the 125 strap works the same as the 100 strap for absolute CPU frequency stability, so if anyone is seeing an issue, it's because they haven't accounted for associated domain speeds correctly. Praz's statement is correct for the DRAM frequency in question.

[Praz]

Hello

The original question centered on selecting the appropriate memory divider which is why it was suggested to use the 125 strap instead of altering BCLK. As far as the instability cited CPU only stability would not be affected. If the PLL is set to 100 using a 40x multiplier, 10 using a 400x multiplier or 4000 with a 1x multiplier the end result will be the same and it is unknown to the CPU how the 4000MHz was achieved. Any instability will be elsewhere.

[bhavvv]

Thanks, Im tweaking it further now.

Initial testing shows stability with the CPU at 4250 Mhz, and 3625 Mhz cache at stock volts (previously at 4.2 and 3.6), and my ram currently seems stable at 3250 Mhz 13-13-13-26 with a voltage increase to 1.45v (will try 3333 after, but not going any higher on the ram volts).

[bhavvv]

Well I couldnt get any higher clocks stable at 13-13-13 timings, even 3250 eventually began throwing up errors in Memtest.

However 14-14-14-1T 3333 Mhz is stable, and at much lower voltage (1.4v) than 3200 @ 13-13-13-1T (1.425v).

Im going to keep that setting for the lower volts.

Also I couldnt boot with 3350 Mhz, it seems the 3333 Mhz rating on this motherboard is pretty literal (3400 doesnt even boot with 2T).

[Craig]

bhavvv wrote:
Well I couldnt get any higher clocks stable at 13-13-13 timings, even 3250 eventually began throwing up errors in Memtest.

However 14-14-14-1T 3333 Mhz is stable, and at much lower voltage (1.4v) than 3200 @ 13-13-13-1T (1.425v).

Im going to keep that setting for the lower volts.

Also I couldnt boot with 3350 Mhz, it seems the 3333 Mhz rating on this motherboard is pretty literal (3400 doesnt even boot with 2T).

To get it to boot at 3400 on the ram, you may well need to adjust your system agent voltage. My Corsair Dominators are rated for 3400 and they need 1.35 volts on the system agent to run at that speed.