Tref values

**amrgb** · 06-19-2005, 01:24 PM

Nice investigation.

But I got lost somewhere when you say that for instance 100 -> 120 Mhz and not 100 -> 233 Mhz. How can you be so sure of this?

If I understood it right the 3632 Tref setting is in fact a 1872 value (3632= 120mhz -> 1872) and it's the bios who label it wrongly. Is that what you mean? I can't see why will they label it in this way.

(If I got it right) According to you theory, the Tref of 0064 is in fact 2808. How can you explain the fact that this setting is extremely slow and even freezes several people's systems?

**astaris** · 06-19-2005, 02:31 PM

But I got lost somewhere when you say that for instance 100 -> 120 Mhz and not 100 -> 233 Mhz. How can you be so sure of this?

Well if you set 100 on the DRAM MEMCLK Frequency field you get the 120 Mhz Mem Divider. Now if you want a 15.6 us Refresh rate when you run this divider, you need a 15.6 us 120 Mhz refresh rate. So if the Cpu Memory controller has the 120 Mhz Mem Divider option, a 15.6 us 120 Mhz Tref setting must be present. On the Athlon 64 the DRAM MEMCLK Frequency can be programmed in order to have lower divider than 1:1, but in this case we have:
100 -> 216 Mhz
101 -> 233 Mhz
110 -> 250 Mhz
So 100 can be 120 Mhz or 216 Mhz. Anyway on the DFI you cannot choose these dividers, so 100 has to be 120 Mhz.

If I understood it right the 3632 Tref setting is in fact a 1872 value (3632= 120mhz -> 1872) and it's the bios who label it wrongly. Is that what you mean? I can't see why will they label it in this way.

They label it wrongly cause they assumed 100 = 233 Mhz, but i'm pretty sure that 100 = 120 Mhz.

(If I got it right) According to you theory, the Tref of 0064 is in fact 2808. How can you explain the fact that this setting is extremely slow and even freezes several people's systems?

Well i don't know why on the bios you have these odd settings, 16, 32, 64 and 128. But i'm sure that:
16 -> 10111
32 -> 01111
64 -> 00111
128 -> 11111
Now these settings are all undocumented and maybe for these values of the Tref register we have different refresh rates, but hey here i made some hypothesis and there's no way to test the real refresh values.

**amrgb** · 06-19-2005, 03:40 PM

Originally Posted by astaris

...there's no way to test the real refresh values.

Actually there is a way to test if your theory is on the right track or not. In theory a slower Tref will heat up memory modules.

Let's pick the 2064 (15.6 100Mz) and the 4708/292 (1.95 150Mhz). If your right when changing from 2064 to 4708 we should observe a rise in the ram temperature. If the DFI values are right, we should observe the opposite. It's just a question of testing it.

For me it's hard to believe that DFI got it wrong, but definitely this Tref thing is weird. So I'm open to new theories. And you might have one hell of a theory if can be backed up by this temp testing (or another test one can remember of).

**EMC2** · 07-23-2005, 10:01 PM

Originally Posted by astaris

Well i don't know why on the bios you have these odd settings, 16, 32, 64 and 128. But i'm sure that:
16 -> 10111
32 -> 01111
64 -> 00111
128 -> 11111
Now these settings are all undocumented and maybe for these values of the Tref register we have different refresh rates, but hey here i made some hypothesis and there's no way to test the real refresh values.

Well.... actually there is a way to test/verify the Tref values

While I had my DIMMs instrumented anyway, I did

The values for the first 3 sets of TRef in the BIOS are fairly close, including the odd low settings.

The BIOS values are the number of MemClocks between refresh cycles (+/-10%). Divider, multiplier, etc. do not matter... only the actual MemClock period... verified for all pre E-rev A64s.

So:: (1 / MemClock) * Bios_Tref = Refresh Period (+/-10%)

Measured actual TRef values(+/-1 clock) in thumbnail below, along with a table for 200Mhz to 300Mhz MemClock, refresh values in uS.

Peace