Re: [RFA]: hw-glue-bus-mux selection behavior

[Dave Brolley <brolley at redhat dot com>]

Frank Ch. Eigler wrote:

> Hi -
> 
> brolley wrote:
> : [...]
> : > To me, this seems like an unnecessary feature; I'd let the client pick
> : > exactly 0 or 1.
> : 
> : ok -- just trying to be too clever, I guess. How about 0 vs non-zero? 
> : I think there should be some defined behavior for all values.  [...]
> 
> No doubt about that.  Not that I want to get you to go all the way
> on this now, but ideally, setting the selector to any index that does
> not have an configured downstream accessor should be okay, merely cause
> sid::bus::unmapped for all future accesses.  The 0/1 case falls out of
> that automatically, as does future expansion to 2..N downstream
> accessors.

OK -- new patch attached

Right now mux_passthrough_bus returns sid::bus::unpermitted if the 
target bus is NULL. Shall I change that to sid::bus::unmapped?

Dave

Index: include/sidbusutil.h
===================================================================
RCS file: /cvs/cvsfiles/devo/sid/include/sidbusutil.h,v
retrieving revision 1.46
diff -c -p -r1.46 sidbusutil.h
*** sidbusutil.h	2001/03/01 19:18:07	1.46
--- sidbusutil.h	2001/03/28 17:44:13
*************** namespace sidutil
*** 266,274 ****
          assert (t2 != 0);
          t[0] = t1;
          t[1] = t2;
        }
      ~mux_passthrough_bus() {}
!     void switch_bus() { index ^= 1; target = t[index]; }
      
      // Some macros to make manufacturing of the cartesian-product
      // calls simpler.
--- 266,292 ----
          assert (t2 != 0);
          t[0] = t1;
          t[1] = t2;
+ 	t[2] = NULL;
        }
      ~mux_passthrough_bus() {}
!     void switch_bus()
!     {
!       // Switch to the next bus if the current one is valid (0 or 1)
!       if ((index & ~1) == 0)
! 	{
! 	  index ^= 1;
! 	  target = t[index];
! 	}
!     }
!     void select_bus (int i)
!     {
!       // Set index to 2 (error) unless i is 0 or 1
!       if ((i & ~1) == 0)
! 	index = i;
!       else
! 	index = 2;
!       target = t[index];
!     }
      
      // Some macros to make manufacturing of the cartesian-product
      // calls simpler.
*************** namespace sidutil
*** 304,310 ****
    private:
      int index;
      sid::bus** target;
!     sid::bus** t[2];
    };
    
    // The passthrough_word_bus maps memory and either directly passes through to the underlying
--- 322,328 ----
    private:
      int index;
      sid::bus** target;
!     sid::bus** t[3];
    };
    
    // The passthrough_word_bus maps memory and either directly passes through to the underlying