A Little Help Here?

From	rickman <gnuarm@gmail.com>
Newsgroups	comp.lang.forth
Subject	A Little Help Here?
Date	2015-05-12 00:53 -0400
Organization	A noiseless patient Spider
Message-ID	<mis0te$p1v$1@dont-email.me> (permalink)

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I am reading a multiplexed, 3 digit, 7 segment LED display and 
converting it to a number.  I have the code working pretty well except 
that maybe once in a couple of hundred reads it glitches.  I would 
believe I missed something in my code or that the hardware is not 
perfect, but the symptoms don't point to anything I can pin down.

First I read the three bits that indicate which digit is being displayed 
and when that is on a new digit the word exits returning the three bit 
one-hot code (1, 2, 4) to indicate which bit.  For some reason I see 
this routine returning the same digit on two successive calls which it 
is supposed to not do.

Perhaps someone else can spot something I am missing...

: newdigit@ ( c1 -- c2 ) \ sync to new digit
   begin digits@ 2dup = over 0= or key? not and while
   drop delay repeat nip ;

c1 is the last digit code read and c2 should be a different one.  The 
digits@ reads the port with the three bits, one-hot encoded.  The loop 
exits when either the code changes but not if it goes to zero or a key 
is pressed.  Here is the routine that calls this code.

: poll_loop ( -- ) \ read and display succesive digits from LED
   LED_Init
   0 begin
     newdigit@ segments@ conv7segtodec digit. dup 4 =
     if 13 emit cr then 	\ Mecrisp sends LF from CR word
     key? until key drop ;

This word is just reading, repeatedly displaying the digits until it 
gets the last one and starts a new line, nothing complex here.

The only way I can see to debug this problem is with a logic analyzer 
which is going to be a PITA.  Or I can just code around it.  I know 
which digit is returned from the 7 seg > decimal conversion, so if I get 
the same one twice I can ignore it.  I just hate having bugs I don't 
understand.  You never know if they might bite you later.

I am viewing this data on a raspberry Pi running e4thcom which is 
connected to the target via a USB serial interface at 115200 bps.  The 
error always appears to be an isolated double read of different digits, 
so I don't suspect the data path is dropping characters which would 
produce more random stuff.

It is late and I guess I'm getting tried.  I'll hit this again in the 
AM.  Sometimes I think by writing down the problem, but nothing came to 
me this time other than the work around.

-- 

Rick

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A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 00:53 -0400
  Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 03:51 -0400
    Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 03:54 -0400
    Re: A Little Help Here? "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-05-12 04:09 -0400
      Re: A Little Help Here? Tessa Bonting <tessa.bonting@gmail.com> - 2015-05-12 07:48 -0700
        Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 13:51 -0400
          Re: A Little Help Here? "Alex McDonald" <blog@rivadpm.com> - 2015-05-12 19:46 +0100
            Re: A Little Help Here? "Alex McDonald" <blog@rivadpm.com> - 2015-05-12 19:53 +0100
              Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 20:15 -0400
                Re: A Little Help Here? "Elizabeth D. Rather" <erather@forth.com> - 2015-05-12 19:29 -1000
            Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 21:18 -0400
  Re: A Little Help Here? all2001@spambog.com (Wolfgang Allinger) - 2015-05-12 08:37 -0300
    Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-12 20:18 -0400
      Re: A Little Help Here? all2001@spambog.com (Wolfgang Allinger) - 2015-05-12 23:08 -0300
        Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-13 03:31 -0400
          Re: A Little Help Here? all2001@spambog.com (Wolfgang Allinger) - 2015-05-13 07:32 -0300
            Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-13 16:47 -0400
              Re: A Little Help Here? all2001@spambog.com (Wolfgang Allinger) - 2015-05-13 17:48 -0300
                Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-13 22:01 -0400
  Re: A Little Help Here? Tessa Bonting <tessa.bonting@gmail.com> - 2015-05-13 08:56 -0700
  Re: A Little Help Here? Tessa Bonting <tessa.bonting@gmail.com> - 2015-05-13 09:22 -0700
    Re: A Little Help Here? rickman <gnuarm@gmail.com> - 2015-05-13 16:56 -0400

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