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AR# 36221

12.1 Spartan-6 Route - Invalid MCB Tieoff site may be used to source constants resulting in design not working in hardware

Description

My design has an OLOGIC component with an ODDR configured in a clock forwarding circuit using constants on the inputs. I have a constant 0 on the D1 input but the output never goes low. Are there any known issues with this configuration?

Solution

There is a known problem where some I/O tiles contain a TIEOFF component intended for use with MCB circuits that is sometimes incorrectly used for general purpose constant sourcing, especially for ILLOGIC or OLOGIC constant connections as in the circuit described above. This problem exists in ISE 12.1 software only as ISE 11.5 software had the correct behavior and ISE 12.2 software will contain a fix. A patch is available to correct the ISE 12.1 software behavior.

A perl script (tieoff.pl) is available to detect the problem:

-----Cut Here-----
# Run xdl on ncd specified on the command line
@ncd_root=split(/\./,$ARGV[0]);
print "Extracting XDL netlist from $ncd_root[0].ncd ...\n";
`xdl -nopips -ncd2xdl $ncd_root[0]`;
print "Done. Searching for used MCB TIEOFF sites ...\n";

$bad_site_found="false";

open (FILE,"$ncd_root[0].xdl");
while(<FILE>){
chomp;
@fields=split(/\s+/);
if ($fields[0] eq "inst" && $fields[1] =~ "XDL_DUMMY_MCB") {
print "An MCB TIEOFF site is being incorrectly used at site $fields[4]\n";
$bad_site_found="true";
}

}

if ($bad_site_found eq "false") {
print "No MCB TIEOFF sites are incorrectly used in this design.\n";
}

exit;

-----Cut Here-----



Example of failure:

[E:\cases\564740]xilperl h:\tools\tieoff.pl bad_design.ncd

Extracting XDL netlist from bad_design.ncd ...

Done. Searching for used MCB TIEOFF sites ...

An MCB TIEOFF site is being incorrectly used at site TIEOFF_X1Y23

Example of success:

E:\cases\564740]xilperl h:\tools\tieoff.pl test_win32_m53dp.ncd

Extracting XDL netlist from test_win32_m53dp.ncd ...

Done. Searching for used MCB TIEOFF sites ...

No MCB TIEOFF sites are incorrectly used in this design.

Patches are available for ISE 12.1:

Linux 32-bit

http://www.xilinx.com/txpatches/pub/swhelp/ise10_updates/36221_route_121_lin32.tar.gz

To install:
cd $XILNIX
tar zxvf 36221_route_121_lin32.tar.gz

Linux 64-bit

http://www.xilinx.com/txpatches/pub/swhelp/ise10_updates/36221_route_121_lin64.tar.gz

To install:
cd $XILNIX
tar zxvf 36221_route_121_lin64.tar.gz

Windows 32-bit

http://www.xilinx.com/txpatches/pub/swhelp/ise10_updates/36221_route_121_win32.zip

To install, Unzip 36221_route_121_win32.zip in the XILINX install directory while maintaining directory structure.

Windows 64-bit

http://www.xilinx.com/txpatches/pub/swhelp/ise10_updates/36221_route_121_win64.zip

To install, Unzip 36221_route_121_win64.zip in the XILINX install directory while maintaining directory structure.
AR# 36221
Date Created 06/16/2010
Last Updated 12/15/2012
Status Active
Type General Article
Devices
  • Spartan-6 LX
  • Spartan-6 LXT
Tools
  • ISE Design Suite - 12.1