Sensor readings as 1-byte

[Tom Joseph]

Hello Guhan,

The updated sensor-example.yaml has the Rexp field as well. These values 
are  calculated based on the minimum and maximum value of the sensor.

If a temperature sensor has a range of -127 - +128, means y is -127 to 
+128 and the range of x is 0-255.
By substituting x = 0 and y = -127 (k2 is the decimal precision and 
assume in this case as whole nos) implies Bexp = -127.
Similarly substitute x = 255 and y = 128 and M is evaluated as 1.

Regards,
Tom

On Saturday 10 March 2018 08:01 AM, guhan balasubramanian wrote:
> Hi,
>
> According to the IPMI spec, we represent all sensor readings (Volt, 
> Temp, Amp, etc.) as 1-byte.
>
> Since we represent them as 1-byte, we use a linearization formula to 
> convert to actual value as follows:
>
> y = (M*x + B*10^(k1))*10^(k2)
>
> where x is the 1-byte value that is filled in the get sensor reading 
> command.
>
> We see in the ipmitool example on how an example of 3.36 V is 
> represented as 1-byte.
> https://computercheese.blogspot.com/2013/10/ipmi-sensor-reading-conversion-formula.html?q=sensor
>
> Can any one please help on how the values for M, B, k1 and k2 are 
> populated for each sensor?
>
> In the openbmc repo, I believe these values are present in the 
> config.yaml of phosphor-ipmi-sensor-inventory (based on the following 
> sample).
>
> 0xF1:
>   sensorType: 0x01
>   path: /xyz/openbmc_project/sensors/temperature/temp1
>   sensorReadingType: 0x01
> *multiplierM*: 511
> *offsetB*: 0
> *bExp*: 0
>   mutability: Mutability::Write|Mutability::Read
>   serviceInterface: org.freedesktop.DBus.Properties
>   readingType: readingData
>   interfaces:
>     xyz.openbmc_project.Sensor.Value:
>       Value:
>         Offsets:
>           0x0:
>             type: int64_t
>
>
> Thanks,
> Guhan
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ozlabs.org/pipermail/openbmc/attachments/20180310/5387d346/attachment.html>