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Re: Arduino / compilers on uC

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From David Brown <david.brown@hesbynett.no>
Newsgroups sci.electronics.design
Subject Re: Arduino / compilers on uC
Date Wed, 08 Feb 2017 12:30:23 +0100
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On 07/02/17 17:05, dagmargoodboat@yahoo.com wrote:
> On Monday, February 6, 2017 at 11:00:56 PM UTC-5, dagmarg...@yahoo.com wrote:
>> On Monday, February 6, 2017 at 9:55:52 PM UTC-5, Clifford Heath wrote:
> 
>>> I suspect that the EEPROM is operating in "write more zeroes" mode.
>>> Do you get the same problem where the target is not EEPROM?
>>
>> That's not the case.  I loaded 'U.dat.flg' from EEPROM, which initializes
>> U.dat.flg to 0xff. All operations thereafter are in RAM.
>>
>> Perhaps the 'boolean' type never anticipated a variable being assigned
>> an illegal value (neither 1 nor 0) in the first place.  Dunno.
>>
>> A snip of the disassembled code follows.
>>
>> The two cases use different print() calls, indicating the compiler regards
>> the expression results as different types, even though they ought to all
>> be unsigned bytes of whatever type you'd like to call 'em.
>>
>> Note that the assignment
>>    w = (U.dat.flg) ? true : false;
>>
>> generates different code in the two cases, and that different Serial.print()
>> routines are called.  It might be that one of those print calls used in
>> the 'boolean' case trashes R1 where its counterpart in the 'uint8_t'
>> case doesn't.  I don't know.
>  
> [...]
> 
> Here's the problem--in the 'boolean' case, the compiler has optimized out
> my assignment of 'true' or 'false' entirely, and has reasoned that it can
> simply directly load the original, illegally 0xff-valued U.dat.flg into
> (word) w (=R15:R14):
>  
>> ============= 'boolean' (does not work) ==================
>> w = (U.dat.flg) ? true : false;
>>     206c:	e0 90 94 01 	lds	r14, U.dat.flg	; 0x800194 <UserSetupTable+0x54>
>>     2070:	f1 2c       	mov	r15, r1
> 
> The compiler thus defeats my instructions to substitute 'true' or
> 'false' for whatever odd value U.dat.flg happened to inherit from
> the EEPROM.

When you program in C (or almost any other programming language, except
assembly), you do not give the compiler a list of instructions to be
turned into object code.  You give a sequence of instructions for an
"abstract machine", and the compiler will generate code that has the
same visible effect as though it followed the instructions.

It is sometimes a subtle distinction, but it is an important one.  It
means that the compiler can use its knowledge of the program and its
state in order to remove or simplify source code.  It can re-arrange
source code in many ways.  It can remove or re-order anything that does
not affect /visible/ results - volatile accesses, file I/O, program
start and stop, and calling external functions whose effect is unknown
(since such functions might have other visible effects).

By declaring U.dat.flg to be bool, you have given the compiler
information - and it uses that information to generate better code.  If
that information was not correct, you should not have given it to the
compiler.

> 
> If I reverse the positions of 'true' and 'false' in that statement
> creating a toggle--the original code--the compiler only toggles the lsb,
> leaving me with w = 0xff, or 0xfe, both still illegal values.
> 
> 
> By contrast with type 'uint8_t', the compiler generates an actual 0x1,
> then conditionally assigns that, or 0x0, as the result of the expression:
> 
>> ============= uint8_t (works) ==================
>> w = (U.dat.flg) ? true : false;
>> 209c:	ee 24       eor	r14, r14          ;R14 = 0
>> 209e:	e3 94       inc	r14               ;R14 = 1
>> 20a0:	f1 2c       mov	r15, r1
>> 20a2:	80 91 94 01 lds	r24, 0x0194       ; load U.dat.flg into R24
>> 20a6:	81 11       cpse	r24, r1   ; if !=0
>> 20a8:	02 c0       rjmp	.+4       ;   then leave 0x1 in w (R15:R14)
>> 20aa:     e1 2c   mov     r14, r1       ;   else w (R15:R14) = 0.
>> 20ac:     f1 2c   mov     r15, r1 
> 
> Cheers,
> James Arthur
>

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Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 15:43 -0800
  Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 10:58 +1100
    Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 19:09 -0500
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:30 -0800
      Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 21:43 -0500
        Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 19:02 -0800
          Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 23:26 -0500
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 21:05 -0800
      Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 13:55 +1100
        Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:00 -0800
          Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 19:31 +1100
          Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:29 +0100
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-07 07:39 -0800
              Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:24 +0100
                Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 08:36 -0800
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 08:15 +1100
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 15:37 +0100
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 15:35 +0100
          Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-07 08:05 -0800
            Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:30 +0100
  Re: Arduino / compilers on uC mrdarrett@gmail.com - 2017-02-06 15:59 -0800
  Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-06 16:04 -0800
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:41 -0800
      Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 14:08 +1100
        Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:14 -0800
          Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:00 +0000
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 05:42 -0800
              Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 15:07 +0100
                Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-09 09:54 -0800
              Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 15:55 +0000
                Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 08:46 -0800
                Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:42 -0500
                Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 06:54 -0800
                Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-11 07:31 -0800
                Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 07:59 -0800
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-11 17:01 +0000
                Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-11 12:52 -0800
                Re: Arduino / compilers on uC krw@notreal.com - 2017-02-11 18:46 -0500
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-12 10:20 +1100
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:07 +0100
                Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:16 -0500
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:39 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:06 +0100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 15:29 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:49 +0100
                Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-13 10:55 -0500
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 17:09 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-14 09:49 +0100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 16:07 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-14 10:01 +0100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-14 09:49 +0000
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-17 04:21 +1100
                Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-16 14:47 -0800
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 00:17 +0000
          Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 19:49 +1100
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 06:22 -0800
          Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:42 +0100
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 06:57 -0800
              Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 16:12 +0100
              Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 08:24 +1100
  Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 19:08 -0500
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:47 -0800
      Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 21:51 -0500
        Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:39 -0800
          Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:55 -0800
            Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 20:05 +1100
              Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-08 12:26 -0500
                Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-08 12:32 -0500
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-09 08:31 +1100
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-09 08:21 +1100
                Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-08 13:33 -0800
          Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:15 +0000
            Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 05:51 -0800
              Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 16:22 +0000
                Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 16:45 -0500
                Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 16:51 -0500
                Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 09:11 +1100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:45 +0000
                Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-15 10:11 -0500
          Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:57 +0100
      Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:07 +0000
        Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-07 04:01 -0500
          Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 09:40 +0000
            Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-07 05:52 -0500
              Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 11:26 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 12:58 +0100
                Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:52 -0500
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:47 +0000
              Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 14:00 -0500
                Re: Arduino / compilers on uC Tim Wescott <seemywebsite@myfooter.really> - 2017-02-09 13:24 -0600
      Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:52 +0100
    Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:50 +0100
  Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-06 19:49 -0500
  Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-07 12:45 +1000
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:51 -0800
      Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-08 06:35 +1000
        Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-08 06:44 +1000
      Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-07 17:11 -0500
        Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:40 +0100
          Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-08 07:01 -0800
            Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 17:25 +0100
              Re: Arduino / compilers on uC jack4747@gmail.com - 2017-02-09 06:51 -0800
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 16:41 +0100
                Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-09 19:44 -0500
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:14 +0100
                Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 12:57 +0000
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 14:11 +0000
                Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 14:40 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-16 15:58 +0100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 15:56 +0000
                Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 16:45 +0000
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 17:18 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 14:59 +0100
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 14:24 +0000
                Re: Arduino / compilers on uC Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-02-17 21:07 +0200
                Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 20:16 +0000
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 23:28 +0100
                Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-17 10:21 -0500
                Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 16:34 +0100
                Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-09 19:43 -0500
  Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-10 10:41 -0600
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 07:06 -0800
      Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-11 17:09 +0000
    Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:28 +0100
  Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-14 09:59 -0600
    Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-14 13:46 -0800
      Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 10:04 +0100
        Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-15 05:57 -0800
          Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 16:02 +0100
            Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 17:15 +0100
          Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-16 14:19 -0600

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