Re: tasking design for keylock

[Simon Wright <simon@pushface.org>]

"Rolf" <rolf.ebert_nospam_@gmx.net> writes:

> The following problem arose when I was thinking about the design for a
> minimal tasking runtime system.
>
> Many doors are locked by electronic keylocks where one has to type four
> correct keys on a small keyboard (mostly 0 .. 9, *, #) before the lock
> is opened. Now there are requirements
>
> - that the time between the key presses must not exceed 0.5 seconds,
> - and that after the 4th correct key you must not type any key at all
> for at least 0.5 seconds.
>
> How do you model the timing requirements using Ada tasking? (I can
> attach the h/w interrupt from the key press to a protected procedure,
> but I don't know how to proceed from there, i.e. how to cancel or serve
> a timed entry call now)

I may have misunderstood (and I may have got protected types wrong),
but .. assuming the interrupt handling PO is like

protected Interrupt_Handler is
   entry Read_Key (K : out Key);
   entry Handler;
   pragma Interrupt_Handler (Handler);
private
   ...
end Interrupt_Handler;

where Read_Key is released by the Handler entry, then you could

select
   Interrupt_Handler.Read_Key (K);
or
   delay 0.5;
   --  deal with missed input opportunity
end select;

--  repeat the above 3 times more

select
   Interrupt_Handler.Read_Key (K);
   --  deal with additional input
or
   delay 0.5;
   --  now we have the correct number of characters and no more
end select;


Thad doesn't handle multiple keypresses so close together that they
bunch up in the PO, of course.