Groups > comp.arch.embedded > #20099

Re: two fpu compared

From	al.basili@gmail.com (alb)
Newsgroups	comp.arch.embedded
Subject	Re: two fpu compared
Date	2015-02-16 09:47 +0000
Message-ID	<ckdsltF3nboU1@mid.individual.net> (permalink)
References	(1 earlier) <mbht2f$v21$1@dont-email.me> <ck6f5eF66ovU1@mid.individual.net> <mbl4rt$77q$1@dont-email.me> <ckdm8aF22ktU1@mid.individual.net> <mbsb5j$lfq$1@dont-email.me>

Show all headers | View raw

Hi David,

David Brown <david.brown@hesbynett.no> wrote:
[]
> The sooner you get this sorted, the better.  It is usual for there to be
> a certain amount of re-negotiation of specifications during a project's
> lifetime (since few customers really know /exactly/ what they need at
> the beginning, and few developers know /exactly/ what they can deliver).
> But it is never a good idea to start out agreeing to something you know
> is impossible!

Couldn't agree more, we've spent nearly 4 months on spec clarifications 
and we're not done yet!

>> We know what's the precision required on the current output (like 0.1% 
>> FSR) and I could, given the current regulation response, provide what's 
>> the precision required at the output of the floating point calculation 
>> (with the float_to_int as last operation).
>> 
>> This would allow indeed to have a reasonable target for the verification 
>> and avoid unattainable objectives.
>> 
> 
> That sounds a good plan.  It will also ensure that your hardware will
> meet your goals (hint - 10-bit PWM is /not/ good enough for 0.1%
> precision - the LSB in any signal is always noise).

Sometimes a little bit of noise can help. Indeed the noise we get from 
the current reading is injected in the regulation loop and may help get 
the precision wanted. If precision is defined as RMS over the output 
current, my 1-2 LSB can provide a gaussian shape whose RMS (or sigma or 
stdev or FWHM) is exactly my 0.1%. I could have a 1bit output and attain 
the required precision if switching frequency is high enough.

This is a bit OT w.r.t. the current thread and is still an open question 
on my side. I'll post something one day on this other subject, but I'm 
not yet there.

Al

Thread

two fpu compared al.basili@gmail.com (alb) - 2015-02-12 08:30 +0000
  Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-12 10:51 +0100
    Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-13 14:14 +0000
      Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-13 16:23 +0100
        Re: two fpu compared Colin Paul de Gloucester <not_a_real_email@address.com> - 2015-02-13 17:37 +0100
          Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 08:01 +0000
            Re: two fpu compared Colin Paul de Gloucester <not_a_real_email@address.com> - 2015-02-16 11:43 +0100
              Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-17 10:35 +0000
                Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-17 12:18 +0100
                Re: two fpu compared George Neuner <gneuner2@comcast.net> - 2015-02-17 09:26 -0500
                Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-17 16:47 +0100
                Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-17 20:54 +0200
        Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 07:58 +0000
          Re: two fpu compared David Brown <david.brown@hesbynett.no> - 2015-02-16 09:53 +0100
            Re: two fpu compared al.basili@gmail.com (alb) - 2015-02-16 09:47 +0000
              Re: two fpu compared Richard Damon <Richard@Damon-Family.org> - 2015-02-16 08:27 -0500
        Re: two fpu compared Nobody <nobody@nowhere.invalid> - 2015-02-23 00:13 +0000
      Re: two fpu compared George Neuner <gneuner2@comcast.net> - 2015-02-13 18:43 -0500
      Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-14 15:30 +0000
        Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-14 23:19 +0200
          Re: two fpu compared Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-02-14 23:28 +0100
          Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-15 14:33 +0000
            Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-17 20:53 +0200
              Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-18 01:55 +0000
                Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-18 17:54 +0200
                Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-18 16:52 +0000
                Re: two fpu compared Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-02-18 18:12 +0100
                Re: two fpu compared Robert Wessel <robertwessel2@yahoo.com> - 2015-02-18 18:02 -0600
                Re: two fpu compared Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-02-19 09:42 +0200
                Re: two fpu compared Robert Wessel <robertwessel2@yahoo.com> - 2015-02-19 11:04 -0600
                Re: two fpu compared Reinhardt Behm <rbehm@hushmail.com> - 2015-02-19 23:26 +0800
                Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-18 19:18 +0200
                Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-19 02:28 +0200
                Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-19 16:29 +0000
                Re: two fpu compared Dimiter_Popoff <dp@tgi-sci.com> - 2015-02-21 16:07 +0200
  Re: two fpu compared glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-02-12 11:26 +0000
  Re: two fpu compared "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2015-02-12 12:29 +0100
  Re: two fpu compared Dennis <dennis@none.none> - 2015-02-12 09:45 -0600

csiph-web