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From: jeppe@iesd.auc.dk (Jeppe Sommer)
Newsgroups: comp.lang.c++
Subject: Re: Interrupt member functions
Message-ID: <JEPPE.91Feb20132758@red.iesd.auc.dk>
Date: 20 Feb 91 13:27:58 GMT
References: <1991Feb19.191356.25123@athena.mit.edu>
Sender: news@iesd.auc.dk
Organization: Mathematics and Computer Science, University of Aalborg
Lines: 69
In-reply-to: ahodgson@athena.mit.edu's message of 19 Feb 91 19:13:56 GMT

>In article <1991Feb19.191356.25123@athena.mit.edu> ahodgson@athena.mit.edu (Antony Hodgson) writes:

>   Is it possible to have a class member function of type "interrupt"?
>   E.g., I want to do something like the following:

>   class InterruptHandler
>	   {
>	   public:	InterruptHandler();
>		   void install( int InterruptNumber );
>		   void interrupt handler();
>		   ...
>	   };

>   void InterruptHandler::install( int InterruptNumber )
>	   {
>		   ...
>		   setvect( InterruptNumber, InterruptHandler::handler );
>		   ...
>	   }

>   Turbo C++ accepts the class declaration, but returns a type mismatch
>   message when it hits the setvect call.  Apparently, handler is not
>   something it can deal with.  If I define another handler routine that's
>   not a member function, all is well (e.g., void altHandler();) and I
>   can properly install it.  What am I missing here?

Well since you have noticed the error message from your compiler, you
are not missing anything :-). setvect() expects a pointer to a
function - not a pointer to a member function. However, even if
setvect() had accepted a pointer to a member function, knowledge of
which object to apply the member function on _would_ be missing.

Furthermore, don't try to typecast InterruptHandler::handler to a
function pointer - it is likely that a pointer to a member function
occupies more storage than a function pointer (I don't know Turbo
C++). 

A solution to your problem would be to use the strategy shown below :

class InterruptHandler {
  InterruptHandler (int IntrNo) {/* Install interrupt handler */}
  ~InterruptHandler () {/* If last instance, de-install interrupt handler */}
  friend void handler();
  doHandle();
  static int noOfInstances;
  static InterruptHandler* instances[MAX_INTR_HANDLERS][MAX_INTR_NO];
  ...
};

void handler() {
  // 1. Find out the current interrupt no (can you do that on a PC?)
  // 2. Determine which instance the interrupt should be directed to.
  //    How this can be accomplished (if at all), depends on the
  //    context of the interrupt and the members of the
  //    instances (accessible through InterruptHandler::instances).
  // 3. Invoke doHandle on the found instance:
  //        InterruptHandler::instances[foundIndex][intrNo]->doHandle();
}

The 2 dimensional static array of instances is of course a naive
representation. Improve it if naivity annoys you.

This is obviously just a sketch of a solution. But it should give you
enough to be able to complete it.

Regards

Jeppe Sommer
Aalborg University, Department of Mathematics and Computer Science.