Experimental Physics and
Industrial Control System

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 <2020> 2021 2022 2023 2024	Index	1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 <2020> 2021 2022 2023 2024
<== Date ==>		<== Thread ==>

Subject:	Re: StreamDevice "type punning" floating point conversion
From:	Eric Norum via Tech-talk <tech-talk at aps.anl.gov>
To:	"Johnson, Andrew N." <anj at anl.gov>
Cc:	EPICS tech-talk <tech-talk at aps.anl.gov>
Date:	Mon, 28 Sep 2020 10:33:39 -0700

Thanks go out to all the folks who replied to my posting.

I didn’t want to create a custom version of StreamDevice with a converter to handle this and the readback in question is just for a slow ‘comfort’ display so I decided to use a CALC record to do the conversion. I could probably get the CALC _expression_ to fit into a 40 character old-fashioned string value, but I’m keeping all the parentheses for now.

# Convert binary representation of IEEE-754 float

# Doesn't handle -0/NaN/Inf/Denormalized, but good enough for this application

record(calc, "$(P)$(R)FAST:SETPOINT") {

    field(DESC, "Fast setpoint")

    field(INPB, "0x007FFFFF")  # Mantissa

    field(INPC, "0x00800000")  # Hidden bit

    field(INPD, "0x7F800000")  # Exponent

    field(INPE, "0x80000000")  # Sign

    field(INPF, "23")          # Exponent shift

    field(INPG, "150")         # Exponent offset

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

    field(PREC, "6")

}

with corresponding protocol entry which reads the setpoint as a hexadecimal value into the ‘A’ field of the CALC record:

# Get SFP command snapshot

# Setpoint format differs with firmware version

SFP_LAST_CMD {

    out "SFP:LAST_CMD";

    in "#SFP:LAST_CMD:"

       "%*[^:]:%(\$1FAST:CMD)x"

       "%*[^:]:%*[(f)]%(\$1FAST:SETPOINT.A)x"

       "%*[^:]:%(\$1FAST:NONCE)x";

     @mismatch { in "#NAK:%(\$1ErrorCode.VAL)d"; }

}

I have a piece of equipment that returns an IEEE-754 floating point value expressed as a hexadecimal integer. i.e. when the device returns the ASCII string
0xbff9d411
it is sending the value
-1.95178

So far the only way I can figure out how to handle this is to read the value into a ai record RVAL then use a subroutine record with a C union to do the conversion and then store the float value in the ai record VAL. Is there a way to avoid the subroutine record? I’m looking for sort of a combination of a %x and a %R StreamDevice format converter.

--
Eric Norum
wenorum at lbl.gov

References:: StreamDevice "type punning" floating point conversion Eric Norum via Tech-talk; Re: StreamDevice "type punning" floating point conversion Johnson, Andrew N. via Tech-talk

Navigate by Date:: Prev: Re: ADProsilica crashing on RHEL7 3.10.0-1127 Dunning, Michael via Tech-talk; Next: Implementing closed loop on EPICS level Guilherme Jovanini Montagner via Tech-talk; Index: 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 <2020> 2021 2022 2023 2024
Navigate by Thread:: Prev: Re: StreamDevice "type punning" floating point conversion Brown, Garth via Tech-talk; Next: RE: EPICS QT question [SEC=UNCLASSIFIED] STARRITT, Andrew via Tech-talk; Index: 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 <2020> 2021 2022 2023 2024

ANJ, 29 Sep 2020

· Home · News · About · Base · Modules · Extensions · Distributions · Download ·
· Search · EPICS V4 · IRMIS · Talk · Bugs · Documents · Links · Licensing ·

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System