Doing NMEA command sequences with zsh ... ??!!

Doing NMEA command sequences with zsh ... ??!!

[meino.cramer]

Hi,

To my embedded system (which runs zsh on Gentoo Linux ;) ) I have
atteched an GPS receiver chip.
This chip spits out NMEA sentences to an UART and is capable of
receiving NMEA command seqyences.

An NMEA command sequence consist of
$<commandname><parameter,nextparameter,....><*><checksum>

The checksum is the binary XOR of all characters between '$' and '*'.
This checksum is given a an hexadecimal number.

Since it is an embedded system, I would prefer to calculate this
checksum with zsh only since it already runs if I am logged in.

Is that possible in any way?

Thank you very much in advance for any help!
Best regards,
mcc

Re: Doing NMEA command sequences with zsh ... ??!!

[Vasiliy Ivanov]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 13.10.2014 21:58, meino.cramer@gmx.de wrote:
> Hi,
> 
> To my embedded system (which runs zsh on Gentoo Linux ;) ) I have atteched an GPS receiver
> chip. This chip spits out NMEA sentences to an UART and is capable of receiving NMEA command
> seqyences.
> 
> An NMEA command sequence consist of $<commandname><parameter,nextparameter,....><*><checksum>
> 
> The checksum is the binary XOR of all characters between '$' and '*'. This checksum is given a
> an hexadecimal number.
> 
> Since it is an embedded system, I would prefer to calculate this checksum with zsh only since
> it already runs if I am logged in.
> 
> Is that possible in any way?
> 
> Thank you very much in advance for any help! Best regards, mcc

Not digging deep into NMEA stuff, only some related hints:

% integer a b; a=16#e7; b=16#3c; print $(([#16]a^b));
16#DB

% c='abcABC'; for i in ${(s..)c}; do print $((#i)); done
97
98
99
65
66
67




- -- 
Regards,
  Vasiliy Ivanov <beelzebubbie.logs@gmail.com>
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Re: Doing NMEA command sequences with zsh ... ??!!

[Bart Schaefer]

On Oct 13, 11:27pm, Vasiliy Ivanov wrote:
} Subject: Re: Doing NMEA command sequences with zsh ... ??!!
}
} > An NMEA command sequence consist of
} > $<commandname><parameter,nextparameter,....><*><checksum>
} > 
} > The checksum is the binary XOR of all characters between '$' and '*'.
} > This checksum is given a an hexadecimal number.
} 
} Not digging deep into NMEA stuff, only some related hints:
} 
} % integer a b; a=16#e7; b=16#3c; print $(([#16]a^b));
} 16#DB
} 
} % c='abcABC'; for i in ${(s..)c}; do print $((#i)); done
} 97
} 98
} 99
} 65
} 66
} 67

Zsh does support bitwise math ops, so

--- 8< --- snip --- 8< ---
print_nmea () {
  setopt localoptions C_BASES
  integer -i 16 checksum
  local i

  local commandname=$1
  shift
  local parameters=${(j:,:)*}

  local NMEA="$commandname$parameters"

  for i in ${(s..)NMEA}; do
    (( checksum ^= #i ))
  done

  print \$$NMEA\*$checksum
}
--- 8< --- snip --- 8< ---


-- 
Barton E. Schaefer