I must confess that this Tref thing had always intrigued me. Especially the correspondence between the Tref value and the xxxMhz y.yyus in the A64 Tweaker.

Today suddenly one comment from flexy gave me an idea.

Quote Originally Posted by flexy
Wonder if those values are just plain wrong.
What if the A64 Tweaker correspondence is also completely wrong? As far as I know, know one knows how those correspondences were made (is the A64 tweaker's author around here to give us an explanation?).

I've carefully analised the Tref values available at the DFI NF4 bios and excluding the odd values 0016, 0032, 0064 and 0128, I can clearly see 4 (not 8) groups of settings.

Tref* | Dif to previous Tref | refresh time x fsb (Tref formula) *(in order of appearance in the DFI NF4 BIOS)

Group 1
1552 --- 15.57x100 = 1557
2064 512 15.57x133.(3) = 2075
2592 528 15.57x166.(6) = 2594
3120 528 15.57x200 = 3113
3632 512 15.57x233.(3) = 3632
4128 496 15.57x266.(6) = 4151
4672 544 15.57x300 = 4670
0032 ---

Group 2
0776 --- 7.78x100 = 778
1032 256 7.78x133.(3) = 1038
1296 264 7.78x166.(6) = 1297
1560 264 7.78x200 = 1557
1816 256 7.78x233.(3) = 1816
2064 248 7.78x266.(6) = 2075
2336 272 7.78x300 = 2335
0032 ---

Group 3
0388 --- 3.89x100 = 389
0516 128 3.89x133.(3) = 519
0648 132 3.89x166.(6) = 649
0780 132 3.89x200 = 778
0908 128 3.89x233.(3) = 908
1032 124 3.89x266.(6) = 1038
1168 136 3.89x300 = 1167
0016 ---

Group 4
1536 --- 15.69x100 = 1569
2048 512 15.69x133.(3) = 2092
2560 512 15.69x166.(6) = 2616
3072 512 15.69x200 = 3139
3684 612 15.69x233.(3) = 3662
4196 512 15.69x266.(6) = 4185
4708 512 15.69x300 = 4708
0128 ---

Each group has 7 (not 4) entries from 100Mhz to 300Mhz (not 200). Under the assumption that the Tref=refresh time x fsb formula holds (and from what I know at this moment I believe it does),then we have the following relations:
- group 1: 15.6us
- group 2: 7.8us
- group 3: 3.9us
- group 4: 15.6us (again)

The refresh times implied by each group were found minimizing the mean absolute difference between the Tref value and the value given by the formula.

Group 4 is weird, because if the difference between were always 512 (only one exception to this), the implied refresh rate would be either 15.36 or 15.69.

What do you think about that?