FUNCTION TYPBUF(LUN:integer):INTEGER;
   EXTERNAL;
{
*USER*
 
The TYPBUF function returns the current character count in the
typeahead buffer of
the specified lun number in LUN.  Naturally, the lun must be
assigned to a device that has typeahead enabled (like a terminal with
TYPEAHEAD), and the device must be attached.
 
A zero or positive integer returned as the value of TYPBUF will be
the current character count.  A negative integer will be returned if
the lun specified is not a "typeahead" device.  The negative value
will be a directive error code or an IO error code.
 
This routine uses local efn 24, which is reserved for P3UITL use.
 
*ERROR CODES*
 
A returned negative value is either a directive error or an IO error code
resulting from the QIOW SF.GMC call.  Common errors would be:
 
.lit
 
  -7  (IE.DNA) device not attached
  -15 (IE.ABO) request terminated - invalid device or no typeahead
  -96 (IE.ILU) invalid lun number
 
 
*WIZARD*
 
Typeahead count is retrieved using the QIOW SF.GMC function,
specifying the TC.TBF characteristic code.
 
}