Timing Simulation - (ModelSim)

[Abs]

HI.

Well this FAQ has been very kind to me and wish it to be the same for
all learners.
What my main prob is, i want to learn "TIMING SIMULATION". I'am
basically a Front end Verification engineer, i have no idea on Timing
Simulation. SUppose i have a simple design in VHDL. say a counter. i
have done the functionality simulation and now want to try out the
timing simualtion. i was told timing sim. is only for designers and not
for verification engineers. But i want to get some idea may never know
when it will be help full.

I just tried out the timing simulation run and i found out that i need
to add few libraries and few files. (guess the library files are for
ModelSim) i have no idea what i'am supposed to do or what files and
libraries i need to add in order to get the simulation. I'am using
Xilinx editor and ModelSim Simulation tool. could anyone out here plz
tell me, how to generate a file from modelsim after functionality
simulation and what kind of files to add.it will be really helpfull.

Thanks and lots.
CHEERS!!

 

[Hubble]

Suppose i have a simple design in VHDL. say a counter. i
have done the functionality simulation and now want to try out the
timing simualtion. i was told timing sim. is only for designers and not
for verification engineers. But i want to get some idea may never know
when it will be help full.

You will need a timing model of your design. This is usually done by a
synthesis tool
like Synopsys Design Compiler or Leonardo Spectrum and a Layout Tool.

1. Synthesis.
==========
The synthesis tools create a netlist with some asumptions on timing.
The netlist
can be a VHDL (or Verilog) netlist. Then, a SDF file provides the
timing, usually for
min, max and typ. (SDF stands for Standard delay format)

Max timing gives the overall max frequency. If you exceed the max
frequency,
the setup time at the longest (logic) path in the design is violated.
But min timing is also important, since many components like ffs have
hold times.
Say, a DFF needs >10 ps before the clock to deliver a stable output at
Q.

The clock is also not exaclty delivered to all components, which is an
issue
if the logic beween two stages is faster than the uncertainty of the
clock
(say: clock tree).

2. Layout
=======
The layout tool leaves the netlist (mostly) alone, but provides
another,
now correct, SDF file containing all min/max/typ times for all paths.

3. Analysis of the timing
==================
Timing analysis can be done
a) statically by a static timing analysis (which uses algorithms to
discover hold/setup
violations/longest paths a.s.o.)

b) by simulation
You have a model (your counter) and a testbench
You have a netlist with a VHDL and SDF file

Then:
Keep the testbench, but replace the model with the VHDL netlist.

The testbench with the VHDL-netlist and the SDF-File can be loaded
into,
say, the modelsim simulator doing a simulation. The netlist
replaces your design
with the output of the synthesis/layout.

On simulation of the netlist (which is timing simulation), all
tests must (should) pass.
The simulation must not (shoud not) output timing violations (setup
or hold
violations).

Simulate min/max conditions separately (selectable in the
simulator).
If you select max SDF Timings, the simulation will represent the
correct timing under
low voltage/high temperator (e.g. 3.0V, 85°C).

If you select min SDF timings, the simulation will represent the
correct timing under
high voltage/low temperator (e.g. 3.6V, -25°C).

4. What is it for
===========
The static timing analysis is absolutely required, since simulation
cannot simulate
*all* paths in compex designs. (Example 32x32 bit multiplier needs
2**64 inputs
to do a full simulation - impossible).

Timing simulation gives a confidence on the correctness of the
synthesis/layout.

5. Further comments
===============
The designs should be synchroneous with few (only one) clocks (say
clock domains).
Then:
* The setup/hold timings can be detected automatically for internal
designs
* Internal timing is mostly verified by static timing analysis.
* you must specify timing requirements for inputs/outputs and clock
domain crossings.
* The timings at the I/O pins and crossings can be verified by
timing simulation

Detection of setup/hold time violations is much more precise if you use
only
master/slave flip flops (say: registers) an NO (!) latches, which also
reduces spikes.

Hubble.

 

[Abs]

Hey Hubble..
thanks a lot....
will implement this idea. very usefull note though. thanks a lot.

cheers Abs

 

[backhus]

Hey Hubble..
thanks a lot....
will implement this idea. very usefull note though. thanks a lot.

cheers Abs

Hi Abs,
very good posting from Hubble.
Maybe you already have discovered that the Xilinx Tools (ISE) create you
all the necessary files (Netlist, SDF) for timing simulation. It can be
found in the PAR section of the implementation tools.

have a nice simulation
Eilert

 

[Abs]

HI,

thanks for all your support, i landed up in some kind of warning. Cant
really figure out what it is, what it basically tries to signify.

the warning is:
----------------------------------------------------------------------------------------------------------------
Started process "Generate Post-Map Simulation Model".

WARNING:Anno:28 - This .ncd is not completely routed; therefore, some
delay
calculations may be inaccurate.
Completed process "Generate Post-Map Simulation Model".
----------------------------------------------------------------------------------------------------------------

I then loaded the netlist and the SDF file and tried to do the timing
simulation and i got this warning in my modelSim Simulator.
----------------------------------------------------------------------------------------------------------------
# Reading C:/Modeltech_xe/tcl/vsim/pref.tcl
# do fibo_tb_fibo_vhd_tb.tdo
# ** Warning: (vlib-34) Library already exists at "work".
# Model Technology ModelSim XE II vcom 5.8c Compiler 2004.03 Mar 26
2004
# -- Loading package standard
# -- Loading package std_logic_1164
# ** Error: (vcom-19) Failed to access library 'simprim' at
"C:\Modeltech_xe\win32xoem/../xilinx/vhdl/simprim".
# No such file or directory. (errno = ENOENT)
# ** Error: fibo_timesim.vhd(18): Library simprim not found.
# ** Error: fibo_timesim.vhd(19): Unknown identifier 'simprim'.
# ** Error: fibo_timesim.vhd(20): Unknown identifier 'simprim'.
# ** Error: fibo_timesim.vhd(22): VHDL Compiler exiting
# ** Error: C:/Modeltech_xe/win32xoem/vcom failed.
# Error in macro ./fibo_tb_fibo_vhd_tb.tdo line 6
# C:/Modeltech_xe/win32xoem/vcom failed.
# while executing
# "vcom -87 -explicit fibo_timesim.vhd
# "
----------------------------------------------------------------------------------------------------------------

Could i get info and help regarding what this is, and how am i suposed
to carry on with the timing simulation.

Thanks and regards...

 

[Hubble]

Abs schrieb:

the warning is:
----------------------------------------------------------------------------------------------------------------
Started process "Generate Post-Map Simulation Model".

WARNING:Anno:28 - This .ncd is not completely routed; therefore, some
delay
calculations may be inaccurate.
Completed process "Generate Post-Map Simulation Model".
----------------------------------------------------------------------------------------------------------------

I then loaded the netlist and the SDF file and tried to do the timing
simulation and i got this warning in my modelSim Simulator.
----------------------------------------------------------------------------------------------------------------
# Reading C:/Modeltech_xe/tcl/vsim/pref.tcl
# do fibo_tb_fibo_vhd_tb.tdo
# ** Warning: (vlib-34) Library already exists at "work".
# Model Technology ModelSim XE II vcom 5.8c Compiler 2004.03 Mar 26
2004
# -- Loading package standard
# -- Loading package std_logic_1164
# ** Error: (vcom-19) Failed to access library 'simprim' at
"C:\Modeltech_xe\win32xoem/../xilinx/vhdl/simprim".
# No such file or directory. (errno = ENOENT)
# ** Error: fibo_timesim.vhd(18): Library simprim not found.
# ** Error: fibo_timesim.vhd(19): Unknown identifier 'simprim'.
# ** Error: fibo_timesim.vhd(20): Unknown identifier 'simprim'.
# ** Error: fibo_timesim.vhd(22): VHDL Compiler exiting
# ** Error: C:/Modeltech_xe/win32xoem/vcom failed.
# Error in macro ./fibo_tb_fibo_vhd_tb.tdo line 6
# C:/Modeltech_xe/win32xoem/vcom failed.
# while executing
# "vcom -87 -explicit fibo_timesim.vhd
# "

You need to install the (Xilinx) SIMPRIM libraries. Probably

http://www.sital.co.il/pdf/Xilinx_VHD_gtl.pdf

shoud help you

Hubble

 

[Abs]

Hi Hubble
thanks for your speedy reply..
well, i wana know, how d i tackle with this issue.


for my former prob. all i need to do is, is install the required
labrary, SPRIM.

Thanks.
Cheers

 

[Hubble]

Abs schrieb:

----------------------------------------------------------------------------------------------------------------

for my former prob. all i need to do is, is install the required
labrary, SPRIM.

This seems to be a XILINX problem (I'm not a XILINX expert). I think
the SDF is imcomplete.
Maybe have a look at the output of XILINX par tool. Are there any
syntax errors in your UCF file?

Hubble.