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Message ID: 16324     Entry time: Mon Sep 13 18:19:25 2021
Author: Tega 
Type: Update 
Category: Computer Scripts / Programs 
Subject: Moved modbus service from chiara to c1susaux 

[Tega, Anchal, Paco]

After talking to Anchal, it was made clear that chiara is not the place to host the modbus service for the temperature sensors. The obvious machine is c1pem, but the startup cmd script loads c object files and it is not clear how easy it would integrate the modbus functionality since we can only login via telnet, so we decided to instead host the service on c1susaux. We also modified the /etc/motd file on c1susaucx which displays the welcome message during login to inform the user that this machine hosts the modbus service for the temperature sensor. Anchal plans to also document this information on the temperature sensor wiki at some point in the future when the page is updated to include what has been learnt so far.

We might also consider updating the database file to a more modern way of reading the temperature sensor data using FLOAT32_LE which is available on EPICs version 3.14 and above, instead of the current method which works but leaves the reader bemused by the bitwise operations that convert the two 16 bits words (A and B) to IEEE-754 32-bit float, via 

field(CALC, "(A&D?(A&C?-1:1):0)*((G|A&E)*J+B)*2^((A&D)/G-F)")

where 

   field(INPA, "$HiWord")
   field(INPB, "$LoWord")
   field(INPC, "0x8000")   # Hi word, sign bit
   field(INPD, "0x7F80")   # Hi word, exponent mask
   field(INPE, "0x00FF")   # Hi word, mantissa mask (incl hidden bit)
   field(INPF, "150")      # Exponent offset plus 23-bit mantissa shift
   field(INPG, "0x0080")   # Mantissa hidden bit
   field(INPJ, "65536")    # Hi/Lo mantissa ratio
   field(CALC, "(A&D?(A&C?-1:1):0)*((G|A&E)*J+B)*2^((A&D)/G-F)")
   field(PREC, "4")

as opposed to the more modern form

field(INP,"@asyn($(PORT) $(OFFSET))FLOAT32_LE")
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