Fixing setup and hold violations in Cadence Encounter

[biju4u90]

Hi,
I am new to SOC Encounter and I am using First Encounter. When I try to do the physical design flow, I am having setup violations after nanorouting stage. The violation remains even after optimizing the design. I've read that addition of buffers will resolve the issue. But how can I add buffers in the design?? How can I identify where to put these buffers?

 

[artmalik]

Well the tool will identify the buffers using function statement in the .libs. So any function A=Y will be considered as buffer. You can use eco_opt_design -hold to fix the hold times. I am assuming you will be adding parasitics and other other design rule constraints to EDI interface.

 

[biju4u90]

@artmalik: Thanks for replying. I am using Encounter 9.1 version and there is no eco_opt_design command in the tool. Actually, I am not having any hold violation, but I do have setup violations. Its seen that the setup violation gets reduced if I optimize the design again and again. After 5 or 6 optimizations, my timing reports show no violations!!.. Is this an acceptable method??
Instead of doing multiple optimizations, how can I resize the cells or add buffers in my design??

- - - Updated - - -

The timing summary is added here.

Before optimization:

+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| -1.304 | -1.304 | 0.185 | -0.455 | N/A | -0.560 |
| TNS (ns):| -44.911 | -43.359 | 0.000 | -1.552 | N/A | -0.930 |
| Violating Paths:| 78 | 60 | 0 | 18 | N/A | 2 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+
+--------------------+---------+---------+---------+---------+---------+---------+
| Hold mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| 0.094 | 0.094 | 2.348 | 0.756 | N/A | 0.250 |
| TNS (ns):| 0.000 | 0.000 | 0.000 | 0.000 | N/A | 0.000 |
| Violating Paths:| 0 | 0 | 0 | 0 | N/A | 0 |
| All Paths:| 553 | 476 | 41 | 41 | N/A | 12 |
+--------------------+---------+---------+---------+---------+---------+---------+

After 1st optimization:
+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| -0.295 | -0.295 | 0.174 | 0.002 | N/A | -0.219 |
| TNS (ns):| -1.059 | -1.059 | 0.000 | 0.000 | N/A | -0.244 |
| Violating Paths:| 9 | 9 | 0 | 0 | N/A | 2 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+

Second optimization:
+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| -0.266 | -0.266 | 0.173 | 0.058 | N/A | -0.266 |
| TNS (ns):| -0.581 | -0.581 | 0.000 | 0.000 | N/A | -0.284 |
| Violating Paths:| 8 | 8 | 0 | 0 | N/A | 2 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+

Third optimization:
+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| -0.050 | -0.050 | 0.180 | 0.060 | N/A | -0.050 |
| TNS (ns):| -0.050 | -0.050 | 0.000 | 0.000 | N/A | -0.050 |
| Violating Paths:| 1 | 1 | 0 | 0 | N/A | 1 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+

Fourth optimization:
+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| -0.125 | -0.125 | 0.179 | 0.021 | N/A | -0.125 |
| TNS (ns):| -0.130 | -0.130 | 0.000 | 0.000 | N/A | -0.125 |
| Violating Paths:| 2 | 2 | 0 | 0 | N/A | 1 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+

After fifth optimization:
+--------------------+---------+---------+---------+---------+---------+---------+
| Setup mode | all | reg2reg | in2reg | reg2out | in2out | clkgate |
+--------------------+---------+---------+---------+---------+---------+---------+
| WNS (ns):| 0.004 | 0.004 | 0.177 | 0.044 | N/A | 0.004 |
| TNS (ns):| 0.000 | 0.000 | 0.000 | 0.000 | N/A | 0.000 |
| Violating Paths:| 0 | 0 | 0 | 0 | N/A | 0 |
| All Paths:| 1087 | 476 | 559 | 57 | N/A | 24 |
+--------------------+---------+---------+---------+---------+---------+---------+