A simple latch functionally simulates properly, but fails in timing simulation.
This is fixed in the latest version of the WebPACK XPLA Fitter Module, which is
available for download at: http://www.xilinx.com/products/software/webpowered.htm
The work-around for older versions of software is to open the time_sim.vhd file and look
for the process statement that contains the latch; add the data input into the sensitivity list.
process(LH, AP, AR, D)
if AR = '1' then
Q_local <= '0' after tar2q;
elsif LH = '1' then
Q_local <= D after tLDI;
elsif AP = '1' then
Q_local <= '1' after tap2q;