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Topic Title: 361MHz Memory Clock on Sempron 3400+
Topic Summary: 371MHz instead of 400, foxconn says 'it is processor fault'
Created On: 12/20/2007 12:25 AM
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 12/20/2007 12:25 AM
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Sergo
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Joined: 02/15/2005

Hi,

I hope somebody from AMD reads this.
I just recently purchased a Sempron 3400+, FOXCONN A690GM2MA mb and Mushkin 2GB HP2-6400, and noticed an interesting bug
(except of cource Catalyst CC not working - ATI's response "our engineers are aware of the problem" - who's "smart" idea was to use .NET??!)

Despite setting memory clock to 400MHz in bios and POST showing 400 during the booting phase, the actual memory clock measured by CPU-Z and FOXONE(utility for info and tweaking from Foxconn). So after a month of quite boring talk with foxconn who did not believe me at first, once there were able to get their hands on the same speed CPU 1.8 Mhz they confirmed the problem and since memory controller is in the cpu ( and even if it wasn't - northbridge is also made by AMD!) they say it's
processor (AMD's) problem. They said they contacted AMD but so far, nothing back.
I hope it would not be just another statement of awareness and marking issue as resolved as they usually do.


With regards,
Sergo.
 12/20/2007 10:15 AM
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go_for
Alpha Geek

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Joined: 01/21/2006

While you are waiting for a more or less official statement from either party, see if you can have the CPU tested in another motherboard.
When you do the memory benchmark using Everest, does it result in 360 MHz comparable figures? Try also memtest86+, it should display whether its running 400MHz ddr or something else.

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 12/21/2007 09:32 PM
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Sergo
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I got an offical responce from AMD.
They say that Sempron AM2 supports aup to 333MHz memory.
"><br ">http://.....set...s/31805.pdf


Strange why then it works at 361 MHz.
Last time when I was checking Semprons specs for S754, 939 models they had the same memory controller as Athlons and only in AM2 they decided to limit it to 333MHz, bummer. I guess it's marketing department's bad influence.
It overclocks fine, but I have to increase bus speed.

And everything would fine, case closed but from my interaction with Foxconn support
when they were trying to reproduce the issue, they sent me this screenshots
for Sempron 3600+.

401 MHZ, NO PROBLEMO.


CPU-Z screehshots
http://img256.imageshack.us/my...ge=memoryspeedal5.png


Apparentlry it was only 3400+ model got castrated.

Edited: 12/21/2007 at 10:01 PM by Sergo
 12/22/2007 01:38 AM
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go_for
Alpha Geek

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So its the FSB : DRAM ratio which does not fit in on this sempron, eg. CPU/5 would be 360MHz. See if you can set CPU/4, that would be ~ 450MHz, a bit over the limit but might just work. On the other hand, if you OC by raising fsb to 220-225MHz, the RAM runs about its right speed.

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Edited: 12/22/2007 at 02:17 AM by go_for
 01/03/2008 09:11 PM
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Sergo
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go_for,

Do you know if it's possible to adjust FSBRAM ratio?
In BIOS I can only see CPU:FSB ratio, and a choice of clock speed for memory.
I don't want to overclock the CPU, just get what I paid for from the memory.
 01/03/2008 11:38 PM
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go_for
Alpha Geek

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I am not familiar with that motherboard, do you have its manual, including the BIOS configuration options?

in BIOS I can only see CPU:FSB ratio, and a choice of clock speed for memory.
It sounds as if it would be possible to adjust to get it closer to correct.

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 01/04/2008 11:01 PM
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MU_Engineer
Dr. Mu

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It is certainly possible to adjust HT clock (K8s have no FSB) :RAM ratio in the BIOS. You will see a menu like so:

DDR2-400 [ ]
DDR2-533 [ ]
DDR2-667 [ ]
DDR2-800 [ ]
DDR2-1066 [ ]

This allows you to set the HT clock:RAM ratio. 1:1 would be DDR2-667, so if you want to clock the RAM higher than the HT clock, pick DDR2-800 or -1066.

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 01/05/2008 12:40 AM
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Sergo
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MU_Engineer,

Of course I set to DDR2 clock to 400MHz in BIOS.
and that the number it shows during the post,
the problem is that 3400+ AM2 somehow treat set memory clock command differently from other Semprons (at least 3600+) and Athlons.
Giving the order does not guarantee its execution, the actual freqency is set somehow between 333 and 400.
which doesn't make sense unless you know underlying mechanism for setting the ratios.
 01/05/2008 12:45 AM
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Sergo
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It's
A690GM2MA-8KRS2H

I think the generic BIOS is written by AMD/ATI and most MB manufactures just do the GUI.
 01/05/2008 12:59 AM
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Sergo
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Ok, things starting to get interesting

I tried to set memory 333MHz, and
CPU-Z shows in x64 Windows (maybe it is the problem) 301 Mhz (330-10%)
For 400 Mhz it was 361=400-10%
 01/05/2008 11:07 AM
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MU_Engineer
Dr. Mu

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The memory signal clock speed is half of the rated speed, so DDR2-667 signals at 333 MHz and DDR2-800 signals at 400 MHz. The memory controller runs synchronous with the speed of the RAM:

DDR2-400: 200 MHz signal speed
DDR2-533: 266 MHz signal speed
DDR2-667: 333 MHz signal speed
DDR2-800: 400 MHz signal speed
DDR2-1066: 533 MHz signal speed

The processor speed is calculated by multiplying the signal speed by an integer (whole) number to reach the processor's rated speed. If the signal speed multiplied by a whole number is greater than the processor's rated speed, then the signal speed is reduced until the processor's rated speed is achieved. Here is what happened with your CPU, rated at 1800 MHz:

1. Set the RAM to DDR2-400 speed: Memory clock is 200 MHz, multiply by 9 and you get 1800 MHz. CPU is happy.

2. Set the RAM to DDR2-533 speed: Memory clock is initially 266 MHz. Multiply that by 7 and that yields 1867 MHz, which is over the 1800 MHz rated speed. Multiplying by 6 yields 1600 MHz, which is under 1800 MHz. The processor picks the 7x ratio and drops the memory clock to 257 MHz, which yields the correct 1800 MHz core speed.

3. Set the RAM to DDR2-667 speed: Memory clock is initially 333 MHz. Multiply that by 6 to get 2000 MHz, which is faster than the rated speed. A 5x ratio yields a too-low core speed of 1667 MHz. So the processor picks the 6x ratio and drops the memory clock speed to 300 MHz to yield the correct 1800 MHz core frequency.

4. Set the RAM to DDR2-800 speeds: Memory clock is initially 400 MHz. Multiply that by 5x to reach 2000 MHz, which is too fast. 4x yields a core speed of 1600 MHz, which is too slow. So the processor uses the 5x ratio and a memory clock speed of 360 MHz to reach a correct core speed of 1800 MHz. Note that the Sempron 3600+ that the tech guy used runs at 2000 MHz, which is a perfect fit for the 5x ratio at the normal 400 MHz signal speed.

5. Set the RAM to DDR2-1066 speed. Memory clock is initially 533 MHz. Multiply that by 4x, which gives a too-fast core speed of 2133 MHz. 3x only yields 1600 MHz. The CPU runs with the 4x ratio and a memory speed of 450 MHz.

You got exactly the results that you should get: 1800 MHz doesn't divide evenly into very many memory signal speeds. You appear to have DDR2-1066 in your system, so set the RAM speed selector to DDR2-1066 if you have that option available in the BIOS. If you don't, just run the memory at DDR2-720 (360 MHz) speeds because a single-core Sempron has way more than enough bandwidth at these speeds. Dual-channel DDR2-720 gives 11,520 MB/sec peak bandwidth. Faster single-core Semprons and Athlon 64s in socket 754 ran very nicely on single-channel DDR-400 (3200 MB/sec), so I would not worry one bit. Heck, my dual-core Athlon 64 X2 4200+ in socket 939 only has 6400 MB/sec peak bandwidth.

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 01/07/2008 12:45 AM
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Sergo
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MU_Engineer,
When I was upgrading my system, my idea was to get cheap CPU and fast memory
since I don't play 3D games, and most of the time CPU is waiting for IO.

Do you know where can I find
"AMD Socket AM2 Processor Functional Data Sheet 31117"?
it seems like AMD wants money for it.


I think (at least looking at BIOS info) CPU determines it's speed from a bus speed (200 MHz), not memory clock
In my bios there is a setting for CPU multiplier relative to the bus clock.
So I set to 200x8 = 1600MHz,
it's a integer multiple of 400, so if your theory is correct I should have 400 memory clock as well.
But, I got 321.5 MHz

Setting CPU to 200x4=800, sets memory clock to 160 MHz (instead of 400), and 800=400x2 (integer)

My motherboard doesn't support DDR2-1066 (Sempron support up to DDR2-667)
Unless there is an utility which allows to set it.

In BIOS guide there is

DRAM Configuration High Register Function 2: Offset 94h

Memory Clock Frequency (MemClkFreq) - Bits 2 - 0. This field specifies the frequency of the
DRAM interface (MEMCLK).
000b = 200 MHz
001b = 266 MHz
010b = 333 MHz
011b = 400 MHz
1xxb = reserved

if those resereved values implemented in Sempron we can check DDR2-1066

But my memory is DDR2-800 Mushkin.

Edited: 01/07/2008 at 12:46 AM by Sergo
 01/07/2008 01:27 AM
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go_for
Alpha Geek

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Sergo, not sure if it will work on your system, but you could try A64Info program to see if it can reveal some more options. The latest version is 0.62beta afaik. Its not a solution, but might show a bit more how this is set up.

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 01/08/2008 02:25 PM
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MU_Engineer
Dr. Mu

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The HT bus clock always runs at 200 MHz, and the multiplier to that sets the CPU speed. That is why the CPU does not change speed when running different speeds of memory. The reason why the CPU clock speed has anything to do with supported memory speed is that the memory controller in a K8-class CPU like your Sempron is in the CPU die and as such, runs at the same speed as the rest of the CPU core. There are only integer memory controller/RAM ratios available, so your 1800 MHz Sempron coud theoretically drive memory at the following signal rates:

1800/1 = 1800 MHz (DDR2-3600)*
1800/2 = 900 MHz (DDR2-1800)*
1800/3 = 600 MHz (DDR2-1200)*
1800/4 = 450 MHz (DDR2-900)*
1800/5 = 360 MHz (DDR2-720)
1800/6 = 300 MHz (DDR2-600)
1800/7 = 257 MHz (DDR2-514)
1800/8 = 225 MHz (DDR2-450)
1800/9 = 200 MHz (DDR2-400)

*Not actually available.

All K8 CPUs compute their memory clock by dividing the core clock rate by an integer and then picking the memory clock speed that is closest to the memory's rated speed without going over. Socket 754 and 939 K8s were very easy to work with as the signaling rate for DDR-400 is 200 MHz, which is exactly the same as the HT bus speed, always guaranteeing the memory would run at the full DDR-400. Socket AM2 CPUs like yours have 100 MHz or 200 MHz steps in core frequency and steps in memory signaling rates that are greater than that, which results in memory not running at full speed on all CPUs. K8-based socket AM2 units like your Sempron only support up to DDR2-800 memory speeds. As such, your 1800 MHz unit will only support a divider as low as /5 as that would give the closest value to DDR2-800 without exceeding the 400 MHz DDR2-800 signaling rate. These explain what happened when you played around with the core speeds:

1. Core at 1600 MHz
CPU/5 is as low of a core speed/memory signal speed ratio as your CPU can run, so the resultant 320 MHz clock speed is as fast as it gets at that clock speed.

2. Core at 800 MHz
CPU/5 yields 160 MHz, which is exactly what you saw.

If you want to try an experiment, change the HT speed to 222 MHz from the default 200 MHz. This gives you a core speed of 2000 MHz:

- It will let you run your memory at an even DDR2-800 speed (2000/5)
- It will let you run your memory at an even DDR2-667 speed (2000/6)
- It will run DDR2-533 at 250 MHz (2000/8)
- It will run DDR2-400 at an even DDR2-400 speed (2000/10)

If you don't want to overclock, set your HT speed to 185 MHz. This will give you a core clock speed of 1667 MHz:

- DDR2-667 will run at DDR2-667 speeds (1667/5)
- DDR2-533 will run at 238 MHz instead of 267 MHz (1667/7)
- DDR2-400 will run at 185 MHz (1667/9)

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