Sensor value calculation formula

[Deng Tyler]

Hi Emily, thank for your kindly reply. This is not typo. I want to dispaly
12.0V in ipmitool and my raw data in Dbus is 2100.
I know value x length is 1 byte. I concern that why raw data calculate with
M, rExp before response to ipmitool.

Tyler

Emily Shaffer <emilyshaffer at google.com> 於 2019年3月7日 週四 上午6:47寫道：

> Hi Tyler,Is this a typo? Do you mean you want to display 21.0 in
> ipmitool? I don't know why there is scaling besides power of 10 on
> your raw value. That is odd.Assuming it was a typo, what you want to
> do is set the scale in the sensor info in order to perform /100
> operation. Or you could set the unit, though that might be difficult
> with a /100 (rather than increment of 1000).The scaling with m, rExp,
> etc is because the IPMI protocol has such a narrow field for sensor
> data (1 byte, as you saw; this is value x).So my recommendation to you
> is to use the scale to do your 2100->21.0 rounding when displaying
> output from ipmitool; and then to use your estimated maximum and
> minimum y to try and figure out what kind of coefficients you want to
> use.  This doesn't need to be perfect; you will lose some precision if
> you choose exponents which give you a much wider range than you need,
> but otherwise the operation should be invisible at the other end.If
> you really did mean you want 2100 -> 12.0 then that's a different
> question, which may require some more massaging on one end or another,
> so let us know.
>
> Emily
>
> On Wed, Mar 6, 2019 at 5:33 AM Deng Tyler <tyler.sabdon at gmail.com> wrote:
> >
> > Hi all:
> >     Sensor reading, according to IPMI spec, is calculated as:
> >
> > y = L[(Mx + B * 10^(bExp)) * 10^(rExp)]
> >
> > y: the 'final value' as reported by IPMItool
> > x: 8 bits, unsigned, reading data encoded in IPMI response packet
> > M: 10 bits, signed integer multiplier, multiplierM in YAML
> > B: 10 bits, signed additive offset, offsetB in YAML
> > bExp: 4 bits, signed, bExp in YAML
> > rExp: 4 bits, signed, rExp in YAML
> >
> >  ipmid calculate raw data by
> > double value = variant_ns::get<T>(propValue) * std::pow(10,
> sensorInfo.scale - sensorInfo.exponentR);
> > auto rawData = static_cast<uint8_t>((value - sensorInfo.scaledOffset) /
> sensorInfo.coefficientM);sue
> >
> > I am confused about why process raw data with M and rExp? M, offsetB,
> bExp and rExp shall just responded to ipmitool and calculate with raw
> > data. I thought raw data only need calculated by scale if raw data need
> to be adjust before respond to ipmitool.
> > Now I met a problem, I have a raw data is 2100 and I want to display
> 12.0 in ipmitool sdr command. I don't know how to assign M, rExp and scale
> value in yaml.
> > Could some one tell me how to translate sensor value? tks.
> >
> > Tyler
> >
> >
>
>
> --
> Emily Shaffer
>
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