markdown/gh_discussions/Query/3608.md

# How do I find and view the nets that are causing hold and setup violations?

Tool: OpenSTA

Subcategory: Timing analysis

## Conversation

### oharboe
It want to find and view nets that cause hold violations.

Today I have to wait and hope for a global routing failure to be able to view the nets that cause hold violations in DRC viewer there.

```
Repair setup and hold violations...
TNS end percent 5
[INFO RSZ-0041] Resized 2 instances.
[WARNING RSZ-0062] Unable to repair all setup violations.
[INFO RSZ-0046] Found 2957 endpoints with hold violations.
[INFO RSZ-0032] Inserted 40106 hold buffers.
Placement Analysis
```


### vvbandeira
```tcl
find_timing_paths -path_delay min -slack_max 0
```
@oharboe, Would this work for you?
Note that RSZ just said it had found `2957` hold violations; after inserting the `40106` buffers, there's no warning.
So it is likely that all have been fixed -- see the warning in the line above for a contrast about setup violations.

For setup you would do:
```tcl
find_timing_paths -path_delay max -slack_max 0
```

### oharboe
Found an approach... Here is what I did:

1. create some hold failures by reducing the clock period from 2000 to 1000ps in mock-array, using diff below.
2. There are no timing violations in placement, the timing violations happen after CTS.
3. Modify cts.tcl to write out an ODB file *before* hold cells are inserted and the design is repair. Post repair in CTS there are no violations.

Now I can run commands to examine minimum hold time violations, which will lead to hold cells being inserted.


```
report_checks -path_delay min
Startpoint: io_insRight_0[61] (input port clocked by clock)
Endpoint: ces_0_0 (rising edge-triggered flip-flop clocked by clock)
Path Group: clock
Path Type: min

  Delay    Time   Description
---------------------------------------------------------
   0.00    0.00   clock clock (rise edge)
   0.00    0.00   clock network delay (propagated)
 200.00  200.00 ^ input external delay
   0.00  200.00 ^ io_insRight_0[61] (in)
  10.45  210.45 ^ input1082/Y (BUFx2_ASAP7_75t_R)
   0.04  210.48 ^ ces_0_0/io_ins_right[61] (Element)
         210.48   data arrival time

   0.00    0.00   clock clock (rise edge)
 337.72  337.72   clock network delay (propagated)
   0.00  337.72   clock reconvergence pessimism
         337.72 ^ ces_0_0/clock (Element)
 102.40  440.11   library hold time
         440.11   data required time
---------------------------------------------------------
         440.11   data required time
        -210.48   data arrival time
---------------------------------------------------------
        -229.63   slack (VIOLATED)
```

```
foreach path [find_timing_paths -slack_max 0 -group_count 10 -path_delay min] {puts "[get_property $path slack] [get_property [get_property $path endpoint] full_name]"}
-229.630280 ces_0_0/io_ins_right[61]
-229.599152 ces_0_0/io_ins_right[3]
-229.596451 ces_0_0/io_ins_right[56]
-229.570663 ces_0_0/io_ins_right[51]
-229.570786 ces_0_0/io_ins_right[53]
-229.568649 ces_0_0/io_ins_right[1]
-229.561371 ces_0_0/io_ins_right[14]
-229.517380 ces_0_0/io_ins_right[30]
-229.512604 ces_0_0/io_ins_right[5]
-229.509186 ces_7_0/io_ins_right[61]
```



```
diff --git a/flow/designs/asap7/mock-array/Element/constraints.sdc b/flow/designs/asap7/mock-array/Element/constraints.sdc
index be545b8f..0a66e62e 100644
--- a/flow/designs/asap7/mock-array/Element/constraints.sdc
+++ b/flow/designs/asap7/mock-array/Element/constraints.sdc
@@ -4,7 +4,7 @@ set cols [expr {[info exists ::env(MOCK_ARRAY_COLS)] ? $::env(MOCK_ARRAY_COLS) :
 
 set clk_name clock
 set clk_port_name clock
-set clk_period 2000
+set clk_period 1000
 
 set clk_port [get_ports $clk_port_name]
 create_clock -period $clk_period -waveform [list 0 [expr $clk_period / 2]] -name $clk_name $clk_port
diff --git a/flow/designs/asap7/mock-array/constraints.sdc b/flow/designs/asap7/mock-array/constraints.sdc
index 5d33c792..46b20e5b 100644
--- a/flow/designs/asap7/mock-array/constraints.sdc
+++ b/flow/designs/asap7/mock-array/constraints.sdc
@@ -1,6 +1,6 @@
 set sdc_version 2.0
 
-set clk_period 2000
+set clk_period 1000
 create_clock [get_ports clock] -period $clk_period -waveform [list 0 [expr $clk_period/2]]
 
 set clk_name  clock
diff --git a/flow/scripts/cts.tcl b/flow/scripts/cts.tcl
index 0b7c56b8..2c0c6fef 100644
--- a/flow/scripts/cts.tcl
+++ b/flow/scripts/cts.tcl
@@ -45,6 +45,8 @@ estimate_parasitics -placement
 report_metrics "cts pre-repair"
 utl::pop_metrics_stage
 
+write_db $::env(RESULTS_DIR)/4_1_cts_pre_repair.odb
+
 repair_clock_nets
 
 utl::push_metrics_stage "cts__{}__post_repair"
```


### oharboe
`make gui_cts` ctrl-f and searching for instance `*hold*` is helpful. :-)

From there I can go to the buffer tree, then find the endpoints.


![image](https://github.com/The-OpenROAD-Project/OpenROAD/assets/2798822/bcfc601b-55b6-4a91-aa4c-e58f630c647e)


### maliberty
Various useful patterns at https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts/blob/2734e98ee7c0f6888a686c2ef2445c0bb837ed0f/flow/scripts/save_images.tcl#L59