Re: input time limit

[Geraint Paul Bevan]

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Heather Duman wrote:
| I'm writing some code that calibrates values reported by a sensor. I
| have some criteria that must be met before calibration can occur. After
| these criteria have been met, I have an input (prompt) statement to
| enter the measured value used for calibration. The sensor will continue
| transmitting values even if calibration has not occurred. Is there any
| way to place a time limit on the input request in case it is not
| noticed? We need all values to be recorded, regardless of calibration.
| All of my attempts at using "pause ()" have failed to produce the
| desired result.
|
| Heather Duman
|


I don't know any way of setting a time limit on input, but it should be
possible to do what you want by spawning a separate sub-process to get
the calibration data. If the sub-process writes the data to file, the
main process can pick it up if/when it exist.

The attached files get dummy sensor data and then try to read an input.
If you are quick, the calibration data will be read. If not, the sensor
collection will carry on regardless.


getvalue.m: # ensure that this is executable (chmod +x)

#! /usr/bin/octave -q

printf ( "\n" );
calibration = input ( "Enter a value: " );
save -ascii calibration.dat calibration;
exit;


run.m: # run this from Octave

clear calibration;

function get_sensor_data ()
~  printf ( "Getting data ... " );
~  pause (5);
~  data = rand (1);
~  printf ( "%f\n", data );
endfunction

function prompt_calibration ()
~  delete ( "calibration.dat" );
~  [pid, msg] = fork ();
~  if ( pid == 0 )              
~    # child process
~    exec ( "./getvalue.m", "" );
~  endif
endfunction

function read_calibration ()
~  if ( file_in_path ( ".", "calibration.dat" ) )
~    load -ascii calibration.dat calibration;
~    printf ( "calibration data is %f\n", calibration );
~  else
~    warning ( "no calibration data ... continuing" );
~  endif
endfunction

## main loop
for i = 1 : 5
~  if ( i == 3 )
~    prompt_calibration();
~  endif
~  get_sensor_data();
~  if ( i == 3 )
~    read_calibration();
~  endif
endfor


- --
Geraint Bevan
http://www.mech.gla.ac.uk/~gbevan

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