Synopsys Tutorial: Power Estimation

Power Estimation with OSU Standard Cell Library and Synopsys tools (PrimeTime-Px)

By Syed Haider

Setting Up Standard Cell Library and Project Directory

1. Download Oklahoma State University Library from http://vcag.ecen.okstate.edu/projects/scells/

Specifically, from: http://vcag.ecen.okstate.edu/projects/scells/download/iit_stdcells_v2.3beta/

Download the iitcells_lib_2.3.tar.gz package.

2. untar the library somewhere nice like your home directory where you will really never touch it (i.e. /home/syedh/). The Directory will be called iit_stdcells.

3. Create a project directory somewhere else. (example: mkdir /home/syedh/Project1) In Project1 create another directory called WORK.

4. Back in Project1 directory create an empty file called: .synopsys_dc.setup

This file will specify to Synopsys and design_vision software what libraries you are using. A sample version of the file is listed below. The path after “/home/syedh/” should remain unchanged if this tutorial is being followed correctly!!!

# .synopsys_dc.setup file
# Define the target tehcnology library, symbol library,
# and link libraries
set target_library /home/syedh/iit_stdcells/lib/tsmc018/lib/iit018_stdcells.db
#do not have a symbol library
#set symbol_library

#set link library (set as same as target library)

set link_library “/home/syedh/iit_stdcells/lib/tsmc018/lib/iit018_stdcells.db *”

set designer "Your Name" 

5. Copy /home/syedh/iit_stdcells/lib/tsmc018/lib/iit018_stdcells.v into Project1 Directory.

6. Now it is design time. Create verilog description of something amazing. Here is a design of a full adder and some registers that spans multiple design files (full_adder.v, top.v):

//full_adder.v
//This is a module for a 1 bit Full Adder
module full_adder(a,b, c_in, s, c_out);

input a, b, c_in;
output wire s, c_out;

assign s = a ^ b ^ c_in;
assign c_out = ((a & b)) | (c_in & (a^b)); 

endmodule

//top.v
//This contains a full adder with some registers for input and output.
`timescale 1ns/10ps
module top (clk, a, b, c_in, sum, c_out);

input clk, a, b, c_in;
output sum, c_out;

reg in_a;
reg in_b;
reg sum_reg;
reg c_out_reg;
reg c_in_reg;

full_adder fa1(.a(in_a), .b(in_b), .c_in(c_in_reg), .s(sum), .c_out(c_out));

always @(posedge clk)
begin
in_a = a;
in_b = b;
c_in_reg = c_in;
c_out_reg = c_out;
sum_reg = sum;
end
endmodule

7. Now it is time to create a test bench file to test the design. The things that will be highlighted in purple are system tasks that will create dumps (value change dumps) of signals in your design.

//tb_top.v
//testbench
`timescale 1ns/10ps
module tb_top();

reg clk;
reg a, b, c_in;
wire c_out, sum;

//clocking description
initial
begin
clk = 0;
end


//clock period is #100
always begin
#50
clk = ~clk;
end

//initialize input to full adder
initial begin
a = 0;
b = 0;
c_in = 0;
end

///////////////////////////////
// Toggle the inputs at varying rates
///////////////////////////////

//toggle carry_in
initial begin
#60;
	repeat (50)
	begin
	c_in <= ~c_in;
	#100;
	end
end

//toggle a
initial begin
#60;
	repeat (25)
	begin
	a <= ~a;
	#200;
	end
end

//toggle b and setup vcd dump
initial begin
$dumpfile("dmp_top.vcd"); //read verilog book for more info on system command
$dumpvars(0,top);
#60;
$dumpon;
        repeat (10)
	 begin
	 b <= ~b;
	 #500;
	 end
 $dumpoff;
 $finish;  //ends simulation
 end

//Module under test
top uut(.clk(clk), .a(a), .b(b), .c_in(c_in), .sum(sum), .c_out(c_out));

endmodule

8. Now comes the time to create a synthesized top level design from {full_adder.v top.v}. We are interested in creating a synthesized version of “top”. At command prompt type the following:

Synopsys
design_vision

Now a design_vision gui has started up. In this gui follow these steps:

In Menu: File --> Analyze. A Dialog box will appear called “Analyze Designs”. Click the “Add..” button and add every design file {full_adder.v top.v}. You can do this one file at a time or all at one time by using the CTRL key to select multiple files. After adding all the files press OK.

In Menu: Design --> Elaborate. A Dialog box will appear called “Elaborate Designs”. There will be a drop down selection menu called “Design”. In this selection menu there will be two objects listed: top(verilog) and full_adder(verilog). Make sure that top(verilog) is selected. Press OK.

Now in the Design Vision the “Hier 1” window will have objects listed in it.

In Menu: Design --> Compile. In the dialog box that shows up press OK.

In Menu: File --> Save As. Save the design as a verilog design with a new name (ex. top_syn.v).

9. Exit the gui and in the command prompt type exit to quit out of the design_vision_xg_t shell. Then type exit again to quit Synopsys.

10. Now it is time to simulate the synthesized design, top_syn.v, with the testbench, tb_top.v. The verilog simulator program of Synopsys is called VCX. The first step is to write a script for the simulation:

#vcs_script.scr
#This is a script file for VCX simulator
./tb_top.v
./top_syn.v
-v ./iit018_stdcells.v
+libext+.v +nolibcell +define+VPD+SAIF+VCD+SDF

11. At command prompt type:

Synopsys

Now type:

vcs -f vcs_script.scr

The result of running this command is that an executable called simv is created.

12. Run simv :

./simv

13. Now the file dmp_top.vcd has been created.

14. Now we will use a tool called PrimeTime-Px to get power estimation. The following script called power.scr will be used.

#power.scr
set power_enable_analysis TRUE
set target_library "/home/syedh/iit_stdcells/lib/tsmc018/lib/iit018_stdcells.db"
set link_library "/home/syedh/iit_stdcells/lib/tsmc018/lib/iit018_stdcells.db *"

read_db $target_library
read_verilog top_syn.v
current_design test_inverter
link
read_vcd dmp_top.vcd -strip_path tb_top/uut
create_power_waveforms –output vcd
report_power

15. At the Synopsys command prompt type:

pt_shell

Now run the power.scr:

source power.scr

16. If all went right the output from the script should look something like this:

======================================================================
Summary:
Total number of nets = 11
Number of annotated nets = 11 (100.00%)
Total number of leaf cells = 7
Number of fully annotated leaf cells = 7 (100.00%)
======================================================================

Information: The waveform options are:
                File name:      power_waves.fsdb
                File format:    fsdb
                Time interval:  0.01ns
                Hierarchical level:     all

Information: Power analysis is running, please wait ...

Information: analysis is done for time window (0ns - 5050ns)

****************************************
Report : Event Based Power
Design : top
Version: Z-2007.06-SP3
Date   : Wed Feb 13 14:34:11 2008
****************************************



  Attributes
  ----------
      i  -  Including register clock pin internal power
      u  -  User defined power group

                        Internal  Switching  Leakage    Total
Power Group             Power     Power      Power      Power   (     %)  Attrs
--------------------------------------------------------------------------------
io_pad                     0.0000    0.0000    0.0000    0.0000 ( 0.00%)
memory                     0.0000    0.0000    0.0000    0.0000 ( 0.00%)
black_box                  0.0000    0.0000    0.0000    0.0000 ( 0.00%)
clock_network           3.292e-06    0.0000    0.0000 3.292e-06 (58.67%)  i
register                6.722e-07 4.735e-07 4.822e-10 1.146e-06 (20.42%)
combinational           8.640e-07 3.086e-07 4.037e-10 1.173e-06 (20.90%)
sequential                 0.0000    0.0000    0.0000    0.0000 ( 0.00%)

 Net Switching Power  = 7.821e-07   (13.94%)
 Cell Internal Power  = 4.828e-06   (86.05%)
 Cell Leakage Power   = 8.859e-10   ( 0.02%)
                         ---------
Total Power            = 5.611e-06  (100.00%)

X Transition Power     =    0.0000
Glitching Power        = 2.152e-08

Peak Power             = 4.726e-03
Peak Time              =   550.100