Hello,

I am using Xilinx 9.1i and Modelsim 5.7g. I instantiated a coregen
module for FFT ver 3.2. After successfully synthesizing the module
with the generated xco, I am now trying to simulate the module. The
hierarchy is as follows:
fft_tb => fft_top => fft.v (generated by coregen)

I am using a custom script as follows:
#############################################
vlib work
vlog fft.v "../fft_top.v" fft_tb.v
vsim -t 1ps   -L xilinxcorelib_ver -L unisims_ver -L simprims_ver -lib
work fft_tb_v glbl
view wave
add wave *
add wave /glbl/GSR
do {fft_tb_v.udo}
view structure
view signals
run 1000ns
##############################################
I have compiled simprims, xilinxcorelib and unisim libraries (verilog
versions) and added them to Modelsim. When I select Simulate
Behavioral Model from Xilinx, it opens modelsim and finds all the
xilinx primitives, which fft module calls, except for these:

# ** Error: (vsim-3033) fft.v(10097): Instantiation of
'fft_r22_cnt_ctrl_6' failed. The design unit was not found.
#         Region: /fft_tb_v/uut/U1
#         Searched libraries:
#             C:/Xilinx91i/verilog/mti_se/XilinxCoreLib_ver
#             C:/Xilinx91i/verilog/mti_se/unisims_ver
#             C:/Xilinx91i/verilog/mti_se/simprims_ver
#             work
# ** Error: (vsim-3033) fft.v(10111): Instantiation of
'fft_r22_cnt_ctrl_7' failed. The design unit was not found.
#         Region: /fft_tb_v/uut/U1
#         Searched libraries:
#             C:/Xilinx91i/verilog/mti_se/XilinxCoreLib_ver
#             C:/Xilinx91i/verilog/mti_se/unisims_ver
#             C:/Xilinx91i/verilog/mti_se/simprims_ver
#             work
# ** Error: (vsim-3033) fft.v(10183): Instantiation of
'fft_r22_cnt_ctrl_8' failed. The design unit was not found.
#         Region: /fft_tb_v/uut/U1
#         Searched libraries:
#             C:/Xilinx91i/verilog/mti_se/XilinxCoreLib_ver
#             C:/Xilinx91i/verilog/mti_se/unisims_ver
#             C:/Xilinx91i/verilog/mti_se/simprims_ver
#             work

So I dont understand why these primitives are present in the core and
why are they not subdivided into modules which are present in simprims
library or any xilinx library for that matter.

Is it a problem of using older Modelsim version with new xilinx
version? Do I need to upgrade ips for 9.1, I am currently working with
the ip set provided in xilinx installation?

Any ideas how I can fix the problem?

Thanks in advance

Mansoor

I found a workaround, if the FFT core is generated with bit revered
order instead of Natural Order, then the errors are removed and
simulation runs smoothly.

Mak

makhan wrote:
>  the FFT core is generated with bit revered order 
                                   ^^^^^^^^^^^

Nuff respect?