JC> To act as an interrupt handler, your member function must be static.
Some C++ compilers don't allow the calling convention of a function member 
(even a static one) to be modified, so this isn't universally true.
I encountered this problem when trying to use a static function member as a 
callback to pass to a system API call in IBM VisualAge C++.  The callback had 
to have the "System" calling convention, but static function members had the 
"C++"/"Optlink" calling convention and VAC++ (quite legally) disallowed the 
use of a calling convention modifier on a function member.
In the general case therefore (if one is talking about *all* C++ compilers), 
callback functions, whether for use as interrupt handlers or for passing to 
system APIs, still have to be ordinary functions, not class members.
 ¯ JdeBP ®
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