E1-20: Sensor Values With Base 2

[sblair]

Fish,

You raised some very good questions. These are questions we will need to clarify in a future revision to the standard.

I went back to Wayne Howell who wrote that portion of the original document. Here's his comments on the original thinking:

For SENS_MEMORY or any sensor type using UNITS_BYTE, the prefix is 1024. So using the commenter’s example:

No Prefix - 1024 UNITS_BYTE = 1024 bytes = 1 Kbyte
Kilo prefix - 1 UNITS_BYTE = 1024 bytes = 1 Kbyte
Kilo prefix - 1000 UNITS_BYTE = 1000 Kbytes
Kilo prefix - 1024 UNITS_BYTE = 1 Mbyte

Using milli etc was never considered and should be thought of as undefined.

[peternewman]

Originally Posted by FishAI

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."

I suspect you'll find most controllers are probably just concatenating the PREFIX and UNIT fields together, so the multiplier is more for the device end to ensure it sends the correct value, i.e. you need to divide your bytes measurement by 1024 to get the value you send to the controller.


The real edge case here is if they show mkg or g for grammes!

Originally Posted by FishAI

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?

Originally Posted by sblair

I went back to Wayne Howell who wrote that portion of the original document. Here's his comments on the original thinking:Using milli etc was never considered and should be thought of as undefined.

Couldn't you use 128 millibytes (miB) to represent a bit?!