Re: [lm-sensors] [PATCH] hwmon: it87 support for 16-bit fan reading

[Jean Delvare <khali@linux-fr.org>]

On Sat, 5 Jul 2008 17:49:23 +0200, Bruno Prémont wrote:
> On Sat, 05 July 2008 Jean Delvare <khali@linux-fr.org> wrote:
> > On Sat, 5 Jul 2008 16:22:45 +0200, Bruno Prémont wrote:
> > > Raw sensors readings:
> > > 
> > >   it8712-isa-0e80
> > >   Adapter: ISA adapter
> > >   in0:         +1.17 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in1:         +0.82 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in2:         +3.01 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in3:         +2.93 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in4:         +1.25 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in5:         +1.76 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in6:         +1.60 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in7:         +2.94 V  (min =  +0.00 V, max =  +4.08 V)
> > >   in8:         +3.26 V
> > >   fan1:       3245 RPM  (min =    0 RPM, div = 8)
> > >   fan2:       1520 RPM  (min =    0 RPM, div = 8)
> > >   temp1:       +20.0°C  (low  =  -1.0°C, high = +127.0°C)  sensor > > > thermal diode temp2:       +48.0°C  (low  =  -1.0°C, high > > > +127.0°C)  sensor = thermal diode temp3:       +25.0°C  (low  > > > -1.0°C, high = +127.0°C)  sensor = transistor cpu0_vid:   +1.550 V
> > > 
> > > Bios readings:
> > > 
> > >   CPU Temp: 33°C
> > >   System temp: 45°C
> > >   CPU FAN: 5769 RPM
> > >   Sys FAN: 1496 RPM
> > > 
> > >   CPU Core: 1.1V
> > >   +1.2V:   1.168V
> > >   +3.3V:   3.008V
> > >   +5V:     4.992V
> > >   +1.8V:   1.76V
> > > 
> > > Looking at those values there could be:
> > >   in0 = +1.2V
> > 
> > Unlikely. Vcore is almost always in0, and it seems to be the case
> > here. +1.2V would rather be in4.
> > 
> > >   in2 = +3.3V
> > >   in5 = +1.8V
> > > 
> > > For the other voltages which do seem to be wired somehow even tough
> > > far less are mentionned in BIOS monitoring section it's hard to
> > > tell what they could match...
> > 
> > The IT8712F can only measure voltages up to 4.08V directly. Other
> > voltages need scaling resistors. The nominal voltage after scaling is
> > typically 3V (3/4 of the full scale). in3 and in7 are almost 3V so
> > they are most probably voltages > 4V scaled down. I would guess in3
> > is +5V and in7 maybe 5VSB. Now you have to figure out the scaling
> > factor. 4.992/2.93 = 1.703. Typical factors for +5V are 1.666 and
> > 1.68, the later is the standard for the IT8712F so I'd say that's
> > what you have.
> > 
> > in8 is normally the battery voltage, unscaled.
> > 
> > So my guess for the configuration of your board would be:
> > 
> >    label in0 "Vcore"
> >    label in2 "+3.3V"
> >    label in3 "+5V"
> >    label in4 "+1.2V"
> >    label in5 "+1.8V"
> >    label in7 "5VSB"
> >    label in8 "Vbat"
> > 
> >    compute in3 ((6.8/10)+1)*@ ,  @/((6.8/10)+1)
> >    compute in8 ((6.8/10)+1)*@ ,  @/((6.8/10)+1)
> for second compute you were thinking in7

Oops, yes, of course.

> Why are the compute lines that complex for just multiplying/dividing
> with 1.68? Is this a workaround for floating-point precision issues?

No, libsensors deals with decimals just fine. The above is simply
matching the physical reality: the voltage is scaled down using
resistors of 10 kOhm and 6.8 kOhm. You can write it 1.68 if you prefer,
that doesn't make any difference.

-- 
Jean Delvare

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