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Virtex Primitive Support
name and generates a warning message with the reason for the warning. For
example, MUX5 could be renamed to MUX51 as in the following log sample:
...
================================================================
*
Low Level Synthesis
*
================================================================
WARNING:Xst:79 - Model 'muxf5' has different characteristics in
destination library
WARNING:Xst:80 - Model name has been changed to 'muxf51'
...
•
If the BOX_TYPE attribute is not attached to the MUXF5. Then XST processes this
block as a user hierarchical block. If the name of the user black box is the same as that
of a Virtex primitive, XST renames it to a unique name and then generates a warning
message with the reason for the warning.
To simplify the instantiation process, XST comes with VHDL and Verilog Virtex libraries.
These libraries contain the complete set of Virtex primitives declarations with a BOX_TYPE
constraint attached to each component. If you use:
•
VHDL—You must declare library "unisim" with its package "vcomponents" in your
source code.
library unisim;
use unisim.vcomponents.all;
The source code of this package can be found in the
vhdl\src\unisims_vcomp.vhd file of the XST installation.
•
Verilog— Starting in release 6.1i, the "unisim" library is already precompiled and XST
automatically links it with your design.
Please note that you must use UPPERCASE for generic (VHDL) and parameter (Verilog)
values when instantiating primitives.
For example the ODDR element has the following component declaration in UNISIM
library:
component ODDR
generic
(DDR_CLK_EDGE : string := "OPPOSITE_EDGE";
INIT : bit := '0';
SRTYPE : string := "SYNC");
port(Q : out std_ulogic;
C : in std_ulogic;
CE : in std_ulogic;
D1 : in std_ulogic;
D2 : in std_ulogic;
R : in std_ulogic;
S : in std_ulogic);
end component;
When you instantiate this primitive in your code, the values of DDR_CLK_EDGE and
SRTYPE generics must be in uppercase. If not, XST generates a Warning message stating
that unknown values are used.
XST User Guide
8.1i
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