Topic: cgminer, on ati and setting memory clock (Read 4694 times)

This is a known issue with some (maybe most) 6xxx cards. I think the problem is in the Windows driver so if your on another OS then this might not apply.

The 6000 series cards are extremely unstable at some reduced memory speeds. So in order to prevent people from running their mem in one of these ranges, they just won't accept any value less then 100 or 125 MHz lower then the core speed. My 6850 wouldn't accept anything lower then Core-100 but I heard many people saying the limit was Core-125.

topheroly clued me in to a the workaround a while back. I can't figure out how to quote a different thread so please just follow the link: https://bitcointalksearch.org/topic/unable-to-underclock-mem-using-sapphire-trixx-33276

So after playing around and finding some memory speeds that didn't result in complete graphics corruption within seconds I set myself some preset speeds. So I could launch MSI Afterburner, pick my first preset, close it, relaunch it, pick my second preset, close it, relaunch it, pick my third preset then launch my miner. After confirming everything was running fine I could close Afterburner but would usually leave it running for the monitoring panel.

In the end I got tired of playing with afterburner. Sold my 6850 and bought a 5850. Even undervolted and sporting a more modest overclock, it takes more power to run then my 6850 did but the 50% increase in shaders means I get more MH/J then before the switch.


Good luck.

just a wild stab; try deleting this line:
"gpu-vddc" : "0.000",

Or maybe it is because you have donations at 0 .

interesting i'm thinking the creator of cgminer is maybe following some sort of safety with the o/c options so he doesnt become liable for breaking hardware, not that i would put liability on him personally...

as what your saying seems to make sense, but then doesn't explain how u can use msi afterburner or trixx to set the memory to like 300. To get that to work tho you have to make the program (at least msi afterburner) do with some editing of config files.. and is not supported officially.. so i guess the implementation in cgminer is the "safe" one, tho there should be an advanced option that uses more agressive code to force the clock... with obviously a disclaimer before setting it saying u agree that the programer of cgminer will not be held responsible for any damage caused. heh.

Actually I have the same problem... I've been told that the lowest memory you can get on 6990 is gpu minus 125 = memory clock. For example 830-125=705 memory. If you set 860 gpu - 125 you get 735 memory. This correlation is always working and I can't make it lower... Any advice?

hey dude thanks for the reply, i got no problem with the engine/core clock speed, found the overclock to 885 doesnt give much of an increase other than in temps so i've wound it back to 830.

Its the memory clock that I'm having trouble with.  Currently have it set to 705mhz which is the lowest it will go.

I'm guessing setting the gpu clock to a range only works when u have auto-gpu or auto-fan/both on?

update: just had a play, adjusted the gpu (engine) clock to 865 which caused the memory clock to revert back to default. When trying to set it back to the 705mhz speed it would not stick, lowest it would now go is 740. I also notice the voltage drops when it trys to implement a change to 0.90 and sets the clocks to 250/150 (briefly) then it either reverts to the stock speed or the speed i set.

Is this due to wrong driver/sdk?

With the memclock set to 300 the program reports back a speed of 1250. Lowest I can go where it reports the value as what I specified seems to be 800mhz for the memory. I have a sapphire 6950 unlocked to be a 6970. I just o/c the gpu/mem to stock 6970 and the shaders are unlocked. I'm running Cat 11.10, sdk 2.5 and 2.0.7 cgminer. You think I should go to a different sdk or driver?

Weird. I have no problems running 300 MHz memory with cgminer, with either windows or linux, 2.0.7 or 2.0.8; but I only have 5850s and 5870s. I even think it does it by default.

Can you post your config file and/or startup parameters? (feel free to comment out passwords and stuff)

** i'd post in the cgminer thread, but well can't **

Anyway, cgminer great program love how you can specify memory and engine speed within the program rather than using a seperate overclock tool.

one problem i've found is the underclocking in cgminer doesn't seem to work as good. in a seperate o/c program like say msi afterburner or trixx i can get the memory to sit stable at 300mhz. with cgminer i'm unable to get that speed to set. Also I think at one time I was able to get it to stick but it caused video corruption. This is odd since with the dedicated o/c programs, i was stable at 300mhz for memory and stock 6970 gpu (885) speeds. Yet if i try to use the same via cgminer's gpu management the speed doesn't set or is unstable.

I'm ok with setting it to the lowest it can go for cgminer (which is about 675) but just curious why cgminer can't set my gpu to settings other programs can? Or are those other programs incorrectly reporting the speed? As I do notice when cgminer tries to set the speed it says successful but the returning value for memory has not changed and reverts back to its default clock. Its interesting when the setting does stick in cgminer both the gpu and memory report a speed of 250/150 and when u go proceed (ie press any key) the new setting is displayed.

Is this "fixed" in the newest version or just something I have to live with? (which I can). There is no big deal in performance just the operating temp of the gpu is slightly lower.