Hello,
I do not understand why I am unable to use yacminer.
/
-R 2560 -g 1 --buffer-size 2560 --lookup-gap 8
5*280x
1*7870
8Gb Memory
YACoin N=16 today!
you overrun your GPU's memory with these settings! (R= far too high)
Perhaps these settings work earlier with lower N value but really not with N16.
Look N tables what tell how much
memory N16 need for one calc then you know what is perhaps ok R with lookupgap 8 and your buffer size (your buffer size is ok for 3Gb GPU's).
Also this may give some help
http://www.ultracoin.net/configgen_raw.html(remember select N16)
Btw...how fast hashing you expect with R9 280x with N16?
Many thanks, but buffer don't work

What is the correct hashrate for 280x ?
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If you have R9 280x 3Gb memory right buff value is normally (afaik) 2560 (least if system memory is enough! for whole rig) but.. if lookup gap is 8 and -g1, your -R is far too high. Start tuning with low -R. (also you can try -g 2 but then agen other parameters need be related to it) I will recommend (because problems) that first run only with 1 to 4 r9 280x connected to board and look how you can adjust it for work.
If I remember right it is far below 500hash/s for one 280x.
I use R7 240 4Gb and Nvidia 750Ti's for YAC. (time when I test r9 280x there was too many difficulties and also (perhaps partially due to yacminer when pool diff drops below 1), high power consumption related to hashing speed.
R7 240 and Nvidia 750Ti beats it clearly (with N16, if N is lower situation turn very different)
Example: N14 chacha, My 4x750Ti rigs give around 12.5khash/s (some loss due to risers what affect with Nvidia but not with AMD radeons) and 4xR9 280x give around 17.5khash/s. But Nvidia use lot of less power related to hashrate. With N16 situation is even more bad for R9 280x.
If it is even over 500h/s for one r9 280x then I still use these for YAC and immediately turn my R9 280 rigs to YAC

)
And with N16 it is fun but R7 240 4G start show its advantages. 0.35khash/s and perhaps something like ~25W power (if moderate overclocked). (not system total power but card itself)
Add: just fast tiny test without any fine adjusting for best result. 250-260 hash/s one r9 280x, clocks e 1100 and m 1500 (changing m to 1600 did not give anything)
g 1, l-g 8, buff 2560, R 1260 (crash if try 1280) exept gpu 0 (display) what crash even with this but it can run with R 1220.
I did not test with g 2 or other settings. Rig have 4x r9 280x. and mobo is Asrock H81 BTC and 8Gb mem.