Bulletin number:  352
Products affected: D700E
Description: Using keyboard interruption in TDS3 EXEs
Component:
Date: Fri Oct 26 15:35:27 BST 1990
-----

ISERVER does not have faciltities for detecting unsolicited keyboard
input. All keyboard input must be explicitly polled or demanded from
the transputer using one of the library procedures so.pollkey or
so.getkey.

The keyboard is polled by the code of the TDS while supporting an EXE.
Unfortunately there are a couple of coding errors in this part of the
TDS which make it not work quite as flexibly as it should. The best
workaround is to do explicit keyboard polling from the EXE on the
transputer. Two solutions are presented below:

----------------------------------
Solution 1: Not using ALT at all.

SEQ
  running := TRUE
  WHILE running
    SEQ
      ...  write something to screen
      --{{{  poll the keyboard
      BYTE bkey, bres:
      SEQ
	so.pollkey (from.isv, to.isv, bkey, bres)
	running := bres <> spr.ok
      --}}}
----------------------------------
Solution 2: Taking advantage of forced poll in TDS after any SP transaction

SEQ
  running := TRUE
  WHILE running
    PRI ALT
      keyboard ? key
	running := FALSE
      TRUE & SKIP
	SEQ
	  ...  write something to screen (using channel screen)
	  so.write.string(from.isv,to.isv,"") -- Forces TDS to poll keyboard
----------------------------------

The algorithm determining when a keyboard poll is done inside the TDS
is too complex to state in full here, but it may be useful to know that
in the absence of any activity on the server channels it is kicked by
the clock at intervals which decay slowly from one sixteenth of a
second to half a second. It is also done after any explicit server
transaction or any transaction on TDS filer channels which need to
access the host. It is NOT done (bug?) after outputs on the TDS EXE
parameter channel screen and a continuous stream of outputs on this
channel can mean the timer branch of the ALT will never be taken! Note
that all this applies to set.abort.key testing on kernel channels also.

When a poll occurs the key is immediately output to the EXE on the
channel keyboard.

See also Bulletin 0351.