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Old April 9th, 2021   #1
FishAI
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Join Date: Jul 2019
Posts: 6
Default E1-20: Sensor Values With Base 2

Hello all you great girls and guys,

please help me out again.

Recently my colleague and I discussed one interesting bit of the E1-20 standard. Beneath Table A-14 is the following annotation:
"When a prefix is used with MEMORY, the multiplier refers to binary multiple. i.e. KILO means multiply by 1024."

We had a great argument about this note.
From our understanding this refers to the interpretation of the sensor value received by SENSOR_VALUE, not the representation of this value.
For example, a sensor reporting a present value of 1 with the sensor's prefix being PREFIX_KILO, the sensor reports a true value of 1024 bytes.
It is not reporting 1000 (true) bytes, which should be represented as ~0.98 kibibyte.

However, we did not figured out whether the multiple of 1024 is only valid if and only if the Sensor Type is SENS_MEMORY.
SENS_MEMORY seems to be the closest match to the mentioned MEMORY, but we are unsure whether the standard does mean any memory related types or indeed solely SENS_MEMORY.

For example manufacturer specific parameters using UNITS_BYTE is a big question here. Should the prefix there also be based on the binary multiple?
Or should a device using manufacturer specific parameters report 1024 UNITS_BYTE to mean 1 kibibyte?

If the binary base refers only to SENS_MEMORY:
Does this mean, that any SENSOR_DEFINITION with its sensor type being different from SENS_MEMORY but its unit being UNITS_BYTE, should NOT use 2 as its base?

Also, there is the special case of exponents being less than 1. What would you expect, if any device reports the following values:
SENSOR_DEFINITION: SENS_MEMORY, UNIT_BYTE, PREFIX_MILLI
SENSOR_VALUE: PresentValue: 0x00000120
Obviously the device reports some sort of undefined partially byte. But would you expect a value of 0.288 millibyte or something different?
We do not know any defined prefix for base 2 with the exponent being less than 1 (like kibi for the exponent being 3). Are there any?

What is the correct interpretation of the mentioned note, what are you recommendation?

Best regards,
FishAI
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