Bob Lunn
07/31/97 11:03 AM


>> We've just finished having this discussion a couple of weeks ago.
>> Frankly it cannot be done easily. This is due to the fact that the
                             ^^^^^^^^^^^^
>> system stack isn't mapped into a user accessible address space. So
>> the typical mechanism, stack swapping, isn't available.
       ^^^^^^^^^^^^^^
>
> Guys, this is baloney. There isn't any specific requirement for an
> addressable stack in any of the basic real time programming principles.


     Tom, you're not reading Byron's original message thoroughly.

     Note the words 'easily' and 'typical'.

     Byron is NOT saying that an addressable stack is MANDATORY.

     He is saying that an addressable stack is a convenient means
     for efficiently implementing a context switch.  Context switching
     can be used to implement multi-tasking, which can in turn be used
     to provide real-time behaviour.

     To continue the discussion, you might present a low-latency, pre-
     emptive, context switch using neither a h/w nor s/w stack...

___Bob