Experimental Physics and
Industrial Control System

Hey Richard,

I actually do not know, why your second solution is not working. I have a device with a similar protocol where I use this approach and it works.

Anyhow. You could use your first solution, but exclude the ACK from the checksum with the width/precision flags. From the documentation:

> The width field is the byte number from which to start calculating the checksum. Default is 0, i.e. the first byte of the input or output of the current command. The last byte is precision bytes before the checksum (default 0). For example in "abcdefg%<xor>" the checksum is calculated from abcdefg, but in "abcdefg%2.1<xor>" only from cdef. 

So in your case you could use:

in ACK, STX, "001 f%[^\003]", ETX, "%1<xor8ff>";

Hope this helps!

Florian

Hi,

    I am having problems parsing data from a serial device (ie
obtained using asyn & stream). The normal protocol is to send a
message (with checksum), wait for an ACK character, then read the
reply (which has a checksum).

If I read the ACK and the reply on one line, using the protocol below:

   read_version {
      out STX, "001?f" ETX, "%<xor8ff>";
      in ACK, STX, "001 f%[^\003]", ETX, "%<xor8ff>";
   }


then I get the correct data into my 'stringin' record, but the shell
reports that the checksum is wrong (presumably because the ACK has
been included in the calculation). If I separate out the ACK and the
reply inputs:

   read_version {
      out STX, "001?f" ETX, "%<xor8ff>";
      in ACK;
      in STX, "001 f%[^\003]", ETX, "%<xor8ff>";
   }

then the shell reports no errors, but nothing is placed in my
'stringin' record.

The messages have no terminators, which I guess is part of the
problem. I have tried playing about with 'extrainput', 'maxinput' and
'wait', with no luck. Does anyone have any suggestions for dealing
with this ?

Thanks,
    Richard

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| Dr. Florian Feldbauer                |
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