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Foundation XVHDL, NGDBUILD: ERROR: basnu - logical net "net_name_int" has both active and tristate drivers


Record #2593

Product Family:  Software

Product Line:  Metamor

Problem Title:
Foundation XVHDL, NGDBUILD:  ERROR: basnu - logical net "net_name_int"
has both active and tristate drivers



Problem Description:
Keywords:  ngdbuild, xvhdl, bidirectional pins

Urgency:  Standard

General Description:

NGDBUILD may give error,
"ERROR: basnu - logical net "net_name_int" has both active and
tristate drivers"
or,
"ERROR: basnu - logical net "net_name_int" has multiple
drivers"

when designing bidirectional I/O pins with hierarchical VHDL in
Foundation.


Solution 1:


Due to the hierarchical nature of EDIF and the way in which
Metamor compiles hierarchical VHDL designs, bidirectional I/O
must be fully described in the top-level entity to avoid
illegal connections being made at the boundary of the top-level
entity and the lower-level macros.

For bidirectional pins, the top-level entity should
have the port declared as 'inout', and the 3-state function of
the output should be described in the top-level entity.  The
lower-level entity should therefore have 2 ports, one for the
input side of the bidi pin ('in'), and one for the output side
of the bidi pin ('out').  Additionally, the 3-state enable
signal may also now be an output port of the lower-level macro,
since the output 3-state functionality is now described in the
top-level entity.



End of Record #2593