Sensor value calculation formula

[Emily Shaffer]

It sounds like you may want to convert, on your sensor end, so that
you are expressing 12.0V in DBus. DBus should be holding the value in
units, rather than a raw sensor value. The alternative here would be
for you to put some context-aware conversion into host-ipmid or into
your handler on top of ipmitool, and that's not something anybody
wants :)  Later if you decide to switch to Redfish, you will have the
same problem, due to your value in DBus being a raw reading instead of
something in units.

Is it possible for you to modify your code where the value is being
pushed to DBus?

On Wed, Mar 6, 2019 at 5:54 PM Deng Tyler <tyler.sabdon at gmail.com> wrote:
>
> 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



-- 
Emily Shaffer