about MAINBOARD_POWER_ON_AFTER_POWER_FAIL

[zhu shi song]

I'm using i845gv based MB. The superio is w83627hf . 
I have set
MAINBOARD_POWER_ON_AFTER_POWER_FAIL=MAINBOARD_POWER_ON.Before
linux booting up, I turn off power switch, when turn
on power swith again, MB can boot again.  But when I
have booted linux successfully, I can see the console
and can login linux, at this time I turn off the power
switch and after 10secs then turn on it, MB can't boot
again.
Who have such experience to make mainboard power on
again after power fail using software solution?
tks
zhu

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