# Commit Procedures

## For external developers
See [Submitting Code to VTR](CONTRIBUTING.md#submitting-code-to-vtr).

## For developers with commit rights
The guiding principle in internal development is to submit your work into the repository without breaking other people's work.
When you commit, make sure that the repository compiles, that the flow runs, and that you did not clobber someone else's work.
In the event that you are responsible for "breaking the build", fix the build at top priority.

We have some guidelines in place to help catch most of these problems:

1.  Before you push code to the central repository, your code MUST pass the check-in regression test.
    The check-in regression test is a quick way to test if any part of the VTR flow is broken.

    At a minimum you must run:
    ```shell
    #From the VTR root directory
    $ ./run_reg_test.pl vtr_reg_basic
    ```
    You may push if all the tests return `All tests passed`.

    However you are strongly encouraged to run both the *basic* and *strong* regression tests:
    ```shell
    #From the VTR root directory
    $ ./run_reg_test.pl vtr_reg_basic vtr_reg_strong
    ```
    since it performs much more thorough testing.

    It is typically a good idea to run tests regularily as you make changes.
    If you have failures see [how to debugging failed tests](#debugging-failed-tests).

2.  The automated [BuildBot](http://builds.verilogtorouting.org:8080/waterfall) will perform more extensive regressions tests and mark which revisions are stable.

3.  Everyone who is doing development must write regression tests for major feature they create.
    This ensures regression testing will detect if a feature is broken by someone (or yourself).
    See [Adding Tests](#adding-tests) for details.

4.  In the event a regression test is broken, the one responsible for having the test pass is in charge of determining:
    * If there is a bug in the source code, in which case the source code needs to be updated to fix the bug, or
    * If there is a problem with the test (perhaps the quality of the tool did in fact get better or perhaps there is a bug with the test itself), in which case the test needs to be updated to reflect the new changes.

    If the golden results need to be updated and you are sure that the new golden results are better, use the command `../scripts/parse_vtr_task.pl -create_golden your_regression_test_name_here`

5.  Keep in sync with the master branch as regularly as you can (i.e. `git pull` or `git pull --rebase`).
    The longer code deviates from the trunk, the more painful it is to integrate back into the trunk.

Whatever system that we come up with will not be foolproof so be conscientious about how your changes will effect other developers.

# Running Tests

VTR has a variety of tests which are used to check for correctness, performance and Quality of Result (QoR).

There are 4 main regression tests:

* `vtr_reg_basic`: ~3 minutes serial

    **Goal:** Fast functionality check

    **Feature Coverage:** Low

    **Benchmarks:** A few small and simple circuits

    **Architectures:** A few simple architectures

    This regression test is *not* suitable for evaluating QoR or performance.
    It's primary purpose is to make sure the various tools do not crash/fail in the basic VTR flow.

    QoR checks in this regression test are primarily 'canary' checks to catch gross degredations in QoR.
    Ocassionally, code changes can cause QoR failures (e.g. due to CAD noise -- particularly on small benchmarks); usually such failures are not a concern if the QoR differences are small.

* `vtr_reg_strong`: ~30 minutes serial, ~15 minutes with `-j4`

    **Goal:** Broad functionaly check

    **Feature Coverage:** High

    **Benchmarks:** A few small circuits, with some special benchmarks to exercise specific features

    **Architectures:** A variety of architectures, including special architectures to exercise specific features

    This regression test is *not* suitable for evaluating QoR or performance.
    It's primary purpose is try and achieve high functionality coverage.

    QoR checks in this regression test are primarily 'canary' checks to catch gross degredations in QoR.
    Ocassionally, changes can cause QoR failures (e.g. due to CAD noise -- particularly on small benchmarks); usually such failures are not a concern if the QoR differences are small.

* `vtr_reg_nightly`: ~15 hours with `-j2`

    **Goal:** Basic QoR and Performance evaluation.

    **Feature Coverage:** Medium

    **Benchmarks:** Small-medium size, diverse. Includes:

    * MCNC20 benchmarks
    * VTR benchmarks
    * Titan 'other' benchmarks (smaller than Titan23)

    **Architectures:** A wider variety of architectures

   QoR checks in this regression are aimed at evaluating quality and run-time of the VTR flow.
   As a result any QoR failures are a concern and should be investigated and understood.

* `vtr_reg_weekly`: ~30 hours with `-j2`

    **Goal:** Full QoR and Performance evaluation.

    **Feature Coverage:** Medium

    **Benchmarks:** Medium-Large size, diverse. Includes:

    * VTR benchmarks
    * Titan23 benchmarks

    **Architectures:** A wide variety of architectures

   QoR checks in this regression are aimed at evaluating quality and run-time of the VTR flow.
   As a result any QoR failures are a concern and should be investigated and understood.

These can be run with `run_reg_test.pl`:
```shell
#From the VTR root directory
$ ./run_reg_test.pl vtr_reg_basic
$ ./run_reg_test.pl vtr_reg_strong
```

The *nightly* and *weekly* regressions require the Titan benchmarks which can be integrated into your VTR tree with:
```shell
make get_titan_benchmarks
```
They can then be run using `run_reg_test.pl`:
```shell
$ ./run_reg_test.pl vtr_reg_nightly
$ ./run_reg_test.pl vtr_reg_weekly
```

To speed-up things up, individual sub-tests can be run in parallel using the `-j` option:
```shell
#Run up to 4 tests in parallel
$ ./run_reg_test.pl vtr_reg_strong -j4
```

You can also run multiple regression tests together:
```shell
#Run both the basic and strong regression, with up to 4 tests in parallel
$ ./run_reg_test.pl vtr_reg_basic vtr_reg_strong -j4
```

## Odin Functionality Tests

Odin has its own set of tests to verify the correctness of its synthesis results:

* `odin_reg_micro`: ~2 minutes serial
* `odin_reg_full`: ~6 minutes serial

These can be run with:
```shell
#From the VTR root directory
$ ./run_reg_test.pl odin_reg_micro
$ ./run_reg_test.pl odin_reg_full
```
and should be used when makeing changes to Odin.

## Unit Tests

VTR also has a limited set of unit tests, which can be run with:
```shell
#From the VTR root directory
$ make && make test
```

# Debugging Failed Tests

If a test fails you probably want to look at the log files to determine the cause.

Lets assume we have a failure in `vtr_reg_basic`:

```shell
#In the VTR root directory
$ ./run_reg_test.pl vtr_reg_strong
#Output trimmed...
regression_tests/vtr_reg_basic/basic_no_timing
-----------------------------------------
k4_N10_memSize16384_memData64/ch_intrinsics...failed: vpr
k4_N10_memSize16384_memData64/diffeq1...failed: vpr
#Output trimmed...
regression_tests/vtr_reg_basic/basic_no_timing...[Fail]
 k4_N10_memSize16384_memData64.xml/ch_intrinsics.v vpr_status: golden = success result = exited
#Output trimmed...
Error: 10 tests failed!
```

Here we can see that `vpr` failed, which caused subsequent QoR failures (`[Fail]`), and resulted in 10 total errors.

To see the log files we need to find the run directory.
We can see from the output that  the specific test which failed was `regression_tests/vtr_reg_basic/basic_no_timing`.
All the regression tests take place under `vtr_flow/tasks`, so the test directory is `vtr_flow/tasks/regression_tests/vtr_reg_basic/basic_no_timing`.
Lets move to that directory:
```shell
#From the VTR root directory
$ cd vtr_flow/tasks/regression_tests/vtr_reg_basic/basic_no_timing
$ ls
config  run002  run004
run001  run003  run005
```

There we see there is a `config` directory (which defines the test), and a set of run-directories.
Each time a test is run it creates a new `runXXX` directory (where `XXX` is an incrementing number).
From the above we can tell that our last run was `run005`.
From the output of `run_reg_test.pl` we know that one of the failing architecture/circuit combinations was `k4_N10_memSize16384_memData64/ch_intrinsics`.
Each architecture/circuit combination is run in its own sub-folder.
Lets move to that directory:
```shell
$ cd run005/k4_N10_memSize16384_memData64/ch_intrinsics
$ ls
abc.out                     k4_N10_memSize16384_memData64.xml  qor_results.txt
ch_intrinsics.net           odin.out                           thread_1.out
ch_intrinsics.place         output.log                         vpr.out
ch_intrinsics.pre-vpr.blif  output.txt                         vpr_stdout.log
ch_intrinsics.route         parse_results.txt
```

Here we can see the individual log files produced by each tool (e.g. `vpr.out`), which we can use to guide our debugging.
We could also manually re-run the tools (e.g. with a debugger) using files in this directory.

# Evaluating Quality of Result (QoR) Changes
VTR uses highly tuned and optimized algorithms and data structures.
Changes which effect these can have significant impacts on the quality of VTR's design implementations (timing, area etc.) and VTR's run-time/memory usage.
Such changes need to be evaluated carefully before they are pushed/merged to ensure no quality degredation occurs.

If you are unsure of what level of QoR evaluation is neccessary for your changes, please ask a VTR developer for guidance.

## General QoR Evaluation Principles
The goal of performing a QoR evaluation is to measure precisely the impact of a set of code/architecture/benchmark changes on both the quality of VTR's design implemenation (i.e. the result of VTR's optimizations), and on tool run-time and memory usage.

This process is made more challenging by the fact that many of VTR's optimization algorithms are based heuristics (some of which depend on randomization).
This means that VTR's implementation results are dependent upon:
 * The initial conditions (e.g. input architecture & netlist, random number generator seed), and
 * The precise optimization algorithms used.

The result is that a minor change to either of these can can make the measured QoR change.
This effect can be viewed as an intrinsic 'noise' or 'variance' to any QoR measurement for a particular architecture/benchmark/algorithm combination.

There are typically two key methods used to measure the 'true' QoR:

1. Averaging metrics accross multiple architectures and benchmark circuits.

2. Averaging metrics multiple runs of the same architecture and benchmark, but using different random number generator seeds

    This is a further variance reduction technique, although it can be very CPU-time intensive.
    A typical example would be to sweep an entire benchmark set accross 3 or 5 different seeds.

In practise any algorithm changes will likely cause improvements on some architecture/benchmark combinations, and degredations on others.
As a result we primarily focus on the *average* behaviour of a change to evaluate its impact.
However extreme outlier behaviour on particular circuits is also important, since it may indicate bugs or other unexpected behaviour.

### Key QoR Metrics

The following are key QoR metrics which should be used to evaluate the impact of changes in VTR.

Implementation Quality Metrics:

| Metric                      | Meaning                                                                  | Sensitivity |
|-----------------------------|--------------------------------------------------------------------------|-------------|
| num_pre_packed_blocks       | Number of primitive netlist blocks (after tech. mapping, before packing) | Low         |
| num_post_packed_blocks      | Number of Clustered Blocks (after packing)                               | Medium      |
| device_grid_tiles           | FPGA size in grid tiles                                                  | Low-Medium  |
| min_chan_width              | The minimum routable channel width                                       | Medium\*    |
| crit_path_routed_wirelength | The routed wirelength at the relaxed channel width                       | Medium      |
| critical_path_delay         | The critical path delay at the relaxed channel width                     | Medium-High |

\* By default, VPR attempts to find the minimum routable channel width; it then performs routing at a relaxed (e.g. 1.3x minimum) channel width. At minimum channel width routing congestion can distort the true timing/wirelength characteristics. Combined with the fact that most FPGA architectures are built with an abundance of routing, post-routing metrics are usually only evaluated at the relaxed channel width.

Run-time/Memory Usage Metrics:

| Metric                      | Meaning                                                                   | Sensitivity |
|-----------------------------|---------------------------------------------------------------------------|-------------|
| vtr_flow_elapsed_time       | Wall-clock time to complete the VTR flow                                  | Low         |
| pack_time                   | Wall-clock time VPR spent during packing                                  | Low         |
| place_time                  | Wall-clock time VPR spent during placement                                | Low         |
| min_chan_width_route_time   | Wall-clock time VPR spent during routing at the relaxed channel width     | High\*      |
| crit_path_route_time        | Wall-clock time VPR spent during routing at the relaxed channel width     | Low         |
| max_vpr_mem                 | Maximum memory used by VPR (in kilobytes)                                 | Low         |

\*  Note that the minimum channel width route time is chaotic and can be highly variable (e.g. 10x variation is not unusual). Minimum channel width routing performs a binary search to find the minimum channel width. Since route time is highly dependent on congestion, run-time is highly dependent on the precise channel widths searched (which may change due to perturbations).

In practise you will likely want to consider additional and more detailed metrics, particularly those directly related to the changes you are making.
For example, if your change related to hold-time optimization you would want to include hold-time related metrics such as `hold_TNS` (hold total negative slack) and `hold_WNS` (hold worst negative slack).
If your change related to packing, you would want to report additional packing-related metrics, such as the number of clusters formed by each block type (e.g. numbers of CLBs, RAMs, DSPs, IOs).

### Benchmark Selection

An important factor in performing any QoR evaluation is the benchmark set selected.
In order to draw reasonably general conclusions about the impact of a change we desire two characteristics of the benchmark set:

1. It includes a large number of benchmarks which are representative of the application domains of interest.

    This ensures we don't over-tune to a specific benchmark or application domain.

2. It should include benchmarks of large sizes.

    This ensures we can optimize and scale to large problem spaces.

In practise (for various reasons) satisfying both of these goals simultaneously is challenging.
The key goal here is to ensure the benchmark set is not unreasonably biased in some manner (e.g. benchmarks which are too small, benchmarks too skewed to a particular application domain).

### Fairly measuring tool run-time
Accurately and fairly measuring the run-time of computer programs is challenging in practise.
A variety of factors effect run-time including:

* Operating System
* System load (e.g. other programs running)
* Variance in hardware performance (e.g. different CPUs on different machines, CPU frequency scaling)

To make reasonably 'fair' run-time comparisons it is important to isolate the change as much as possible from other factors.
This involves keeping as much of the experimental environment identical as possible including:

1. Target benchmarks
2. Target architecture
3. Code base (e.g. VTR revision)
4. CAD parameters
5. Computer system (e.g. CPU model, CPU frequency/power scaling, OS version)
6. Compiler version

## Collecting QoR Measurements
The first step is to collect QoR metrics on your selected benchmark set.

You need at least two sets of QoR measurements:
1. The baseline QoR (i.e. unmodified VTR).
2. The modified QoR (i.e. VTR with your changes).

Note that it is important to generate both sets of QoR measurements on the same computing infrastructure to ensure a fair run-time comparison.

The following examples show how a single set of QoR measurements can be produced using the VTR flow infrastructure.

### Example: VTR Benchmarks QoR Measurement

The VTR benchmarks are a group of benchmark circuits distributed with the VTR project.
The are provided as synthesizable verilog and can be re-mapped to VTR supported architectures.
They consist mostly of small to medium sized circuits from a mix of application domains.
They are used primarily to evaluate the VTR's optimization quality in an architecture exploration/evaluation setting (e.g. determining minimum channel widths).

A typical approach to evaluating an algorithm change would be to run `vtr_reg_qor_chain` task from the nightly regression test:

```shell
#From the VTR root
$ cd vtr_flow/tasks

#Run the VTR benchmarks
$ ../scripts/run_vtr_task.pl regression_tests/vtr_reg_nightly/vtr_reg_qor_chain

#Several hours later... they complete

#Parse the results
$ ../scripts/parse_vtr_task.pl regression_tests/vtr_reg_nightly/vtr_reg_qor_chain

#The run directory should now contain a summary parse_results.txt file
$ head -5 vtr_reg_nightly/vtr_reg_qor_chain/latest/parse_results.txt
arch                                  	circuit           	script_params	vpr_revision 	vpr_status	error	num_pre_packed_nets	num_pre_packed_blocks	num_post_packed_nets	num_post_packed_blocks	device_width	device_height	num_clb	num_io	num_outputs	num_memoriesnum_mult	placed_wirelength_est	placed_CPD_est	placed_setup_TNS_est	placed_setup_WNS_est	min_chan_width	routed_wirelength	min_chan_width_route_success_iteration	crit_path_routed_wirelength	crit_path_route_success_iteration	critical_path_delay	setup_TNS	setup_WNS	hold_TNS	hold_WNS	logic_block_area_total	logic_block_area_used	min_chan_width_routing_area_total	min_chan_width_routing_area_per_tile	crit_path_routing_area_total	crit_path_routing_area_per_tile	odin_synth_time	abc_synth_time	abc_cec_time	abc_sec_time	ace_time	pack_time	place_time	min_chan_width_route_time	crit_path_route_time	vtr_flow_elapsed_time	max_vpr_mem	max_odin_mem	max_abc_mem
k6_frac_N10_frac_chain_mem32K_40nm.xml	bgm.v             	common       	9f591f6-dirty	success   	     	26431              	24575                	14738               	2258                  	53          	53           	1958   	257   	32         	0           11      	871090               	18.5121       	-13652.6            	-18.5121            	84            	328781           	32                                    	297718                     	18                               	20.4406            	-15027.8 	-20.4406 	0       	0       	1.70873e+08           	1.09883e+08          	1.63166e+07                      	5595.54                             	2.07456e+07                 	7114.41                        	11.16          	1.03          	-1          	-1          	-1      	141.53   	108.26    	142.42                   	15.63               	652.17               	1329712    	528868      	146796
k6_frac_N10_frac_chain_mem32K_40nm.xml	blob_merge.v      	common       	9f591f6-dirty	success   	     	14163              	11407                	3445                	700                   	30          	30           	564    	36    	100        	0           0       	113369               	13.4111       	-2338.12            	-13.4111            	64            	80075            	18                                    	75615                      	23                               	15.3479            	-2659.17 	-15.3479 	0       	0       	4.8774e+07            	3.03962e+07          	3.87092e+06                      	4301.02                             	4.83441e+06                 	5371.56                        	0.46           	0.17          	-1          	-1          	-1      	67.89    	11.30     	47.60                    	3.48                	198.58               	307756     	48148       	58104
k6_frac_N10_frac_chain_mem32K_40nm.xml	boundtop.v        	common       	9f591f6-dirty	success   	     	1071               	1141                 	595                 	389                   	13          	13           	55     	142   	192        	0           0       	5360                 	3.2524        	-466.039            	-3.2524             	34            	4534             	15                                    	3767                       	12                               	3.96224            	-559.389 	-3.96224 	0       	0       	6.63067e+06           	2.96417e+06          	353000.                          	2088.76                             	434699.                     	2572.18                        	0.29           	0.11          	-1          	-1          	-1      	2.55     	0.82      	2.10                     	0.15                	7.24                 	87552      	38484       	37384
k6_frac_N10_frac_chain_mem32K_40nm.xml	ch_intrinsics.v   	common       	9f591f6-dirty	success   	     	363                	493                  	270                 	247                   	10          	10           	17     	99    	130        	1           0       	1792                 	1.86527       	-194.602            	-1.86527            	46            	1562             	13                                    	1438                       	20                               	2.4542             	-226.033 	-2.4542  	0       	0       	3.92691e+06           	1.4642e+06           	259806.                          	2598.06                             	333135.                     	3331.35                        	0.03           	0.01          	-1          	-1          	-1      	0.46     	0.31      	0.94                     	0.09                	2.59                 	62684      	8672        	32940
```

### Example: Titan Benchmarks QoR Measurements

The Titan benchmarks are a group of large benchmark circuits from a wide range of applications, which are compatible with the VTR project.
The are typically used as post-technology mapped netlists which have been pre-synthesized with Quartus.
They are substantially larger and more realistic than the VTR benchmarks, but can only target specificly compatible architectures.
They are used primarily to evaluate the optimization quality and scalability of VTR's CAD algorithms while targetting a fixed architecture (e.g. at a fixed channel width).

A typical approach to evaluating an algorithm change would be to run `vtr_reg_titan` task from the weekly regression test:

```shell
#From the VTR root

#Download and integrate the Titan benchmarks into the VTR source tree
$ make get_titan_benchmarks

#Move to the task directory
$ cd vtr_flow/tasks

#Run the VTR benchmarks
$ ../scripts/run_vtr_task.pl regression_tests/vtr_reg_weekly/vtr_reg_titan

#Several days later... they complete

#Parse the results
$ ../scripts/parse_vtr_task.pl regression_tests/vtr_reg_nightly/vtr_reg_titan

#The run directory should now contain a summary parse_results.txt file
$ head -5 vtr_reg_nightly/vtr_reg_qor_chain/latest/parse_results.txt
arch                     	circuit                                 	vpr_revision	vpr_status	error	num_pre_packed_nets	num_pre_packed_blocks	num_post_packed_nets	num_post_packed_blocks	device_width	device_height	num_clb	num_io	num_outputs	num_memoriesnum_mult	placed_wirelength_est	placed_CPD_est	placed_setup_TNS_est	placed_setup_WNS_est	routed_wirelength	crit_path_route_success_iteration	logic_block_area_total	logic_block_area_used	routing_area_total	routing_area_per_tile	critical_path_delay	setup_TNS   setup_WNS	hold_TNS	hold_WNS	pack_time	place_time	crit_path_route_time	max_vpr_mem	max_odin_mem	max_abc_mem
stratixiv_arch.timing.xml	neuron_stratixiv_arch_timing.blif       	0208312     	success   	     	119888             	86875                	51408               	3370                  	128         	95           	-1     	42    	35         	-1          -1      	3985635              	8.70971       	-234032             	-8.70971            	1086419          	20                               	0                     	0                    	2.66512e+08       	21917.1              	9.64877            	-262034     -9.64877 	0       	0       	127.92   	218.48    	259.96              	5133800    	-1          	-1
stratixiv_arch.timing.xml	sparcT1_core_stratixiv_arch_timing.blif 	0208312     	success   	     	92813              	91974                	54564               	4170                  	77          	57           	-1     	173   	137        	-1          -1      	3213593              	7.87734       	-534295             	-7.87734            	1527941          	43                               	0                     	0                    	9.64428e+07       	21973.8              	9.06977            	-625483     -9.06977 	0       	0       	327.38   	338.65    	364.46              	3690032    	-1          	-1
stratixiv_arch.timing.xml	stereo_vision_stratixiv_arch_timing.blif	0208312     	success   	     	127088             	94088                	62912               	3776                  	128         	95           	-1     	326   	681        	-1          -1      	4875541              	8.77339       	-166097             	-8.77339            	998408           	16                               	0                     	0                    	2.66512e+08       	21917.1              	9.36528            	-187552     -9.36528 	0       	0       	110.03   	214.16    	189.83              	5048580    	-1          	-1
stratixiv_arch.timing.xml	cholesky_mc_stratixiv_arch_timing.blif  	0208312     	success   	     	140214             	108592               	67410               	5444                  	121         	90           	-1     	111   	151        	-1          -1      	5221059              	8.16972       	-454610             	-8.16972            	1518597          	15                               	0                     	0                    	2.38657e+08       	21915.3              	9.34704            	-531231     -9.34704 	0       	0       	211.12   	364.32    	490.24              	6356252    	-1          	-1
```

## Comparing QoR Measurements
Once you have two (or more) sets of QoR measurements they now need to be compared.

A general method is as follows:
1. Normalize all metrics to the values in the baseline measurements (this makes the relative changes easy to evaluate)
2. Produce tables for each set of QoR measurements showing the per-benchmark relative values for each metric
3. Calculate the GEOMEAN over all benchmarks for each normalized metric
4. Produce a summary table showing the Metric Geomeans for each set of QoR measurments

### QoR Comparison Gotchas
There are a variety of 'gotchas' you need to avoid to ensure fair comparisons:
* GEOMEAN's must be over the same set of benchmarks .
    A common issue is that a benchmark failed to complete for some reason, and it's metric values are missing

* Run-times need to be collected on the same compute infrastructure at the same system load (ideally unloaded).

### Example QoR Comparison
Suppose we've make a change to VTR, and we now want to evaluate the change.
As described above we produce QoR measurements for both the VTR baseline, and our modified version.

We then have the following (hypothetical) QoR Metrics.

**Baseline QoR Metrics:**

| arch                                   | circuit            | num_pre_packed_blocks | num_post_packed_blocks | device_grid_tiles | min_chan_width | crit_path_routed_wirelength | critical_path_delay | vtr_flow_elapsed_time | pack_time | place_time | min_chan_width_route_time | crit_path_route_time | max_vpr_mem |
|----------------------------------------|--------------------|-----------------------|------------------------|-------------------|----------------|-----------------------------|---------------------|-----------------------|-----------|------------|---------------------------|----------------------|-------------|
| k6_frac_N10_frac_chain_mem32K_40nm.xml | bgm.v              | 24575                 | 2258                   | 2809              | 84             | 297718                      | 20.4406             | 652.17                | 141.53    | 108.26     | 142.42                    | 15.63                | 1329712     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | blob_merge.v       | 11407                 | 700                    | 900               | 64             | 75615                       | 15.3479             | 198.58                | 67.89     | 11.3       | 47.6                      | 3.48                 | 307756      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | boundtop.v         | 1141                  | 389                    | 169               | 34             | 3767                        | 3.96224             | 7.24                  | 2.55      | 0.82       | 2.1                       | 0.15                 | 87552       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | ch_intrinsics.v    | 493                   | 247                    | 100               | 46             | 1438                        | 2.4542              | 2.59                  | 0.46      | 0.31       | 0.94                      | 0.09                 | 62684       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq1.v          | 886                   | 313                    | 256               | 60             | 9624                        | 17.9648             | 15.59                 | 2.45      | 1.36       | 9.93                      | 0.93                 | 86524       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq2.v          | 599                   | 201                    | 256               | 52             | 8928                        | 13.7083             | 13.14                 | 1.41      | 0.87       | 9.14                      | 0.94                 | 85760       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU8PEEng.v         | 31396                 | 2286                   | 2916              | 100            | 348085                      | 79.4512             | 1514.51               | 175.67    | 153.01     | 1009.08                   | 45.47                | 1410872     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU32PEEng.v        | 101542                | 7251                   | 9216              | 158            | 1554942                     | 80.062              | 28051.68              | 625.03    | 930.58     | 25050.73                  | 251.87               | 4647936     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mcml.v             | 165809                | 6767                   | 8649              | 128            | 1311825                     | 51.1905             | 9088.1                | 524.8     | 742.85     | 4001.03                   | 127.42               | 4999124     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkDelayWorker32B.v | 4145                  | 1327                   | 2500              | 38             | 30086                       | 8.39902             | 65.54                 | 7.73      | 15.39      | 26.19                     | 3.23                 | 804720      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkPktMerge.v       | 1160                  | 516                    | 784               | 44             | 13370                       | 4.4408              | 21.75                 | 2.45      | 2.14       | 13.95                     | 1.96                 | 122872      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkSMAdapter4B.v    | 2852                  | 548                    | 400               | 48             | 19274                       | 5.26765             | 47.64                 | 16.22     | 4.16       | 19.95                     | 1.14                 | 116012      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | or1200.v           | 4530                  | 1321                   | 729               | 62             | 51633                       | 9.67406             | 105.62                | 33.37     | 12.93      | 44.95                     | 3.33                 | 219376      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | raygentop.v        | 2934                  | 710                    | 361               | 58             | 22045                       | 5.14713             | 39.72                 | 9.54      | 4.06       | 19.8                      | 2.34                 | 126056      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | sha.v              | 3024                  | 236                    | 289               | 62             | 16653                       | 10.0144             | 390.89                | 11.47     | 2.7        | 6.18                      | 0.75                 | 117612      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision0.v    | 21801                 | 1122                   | 1156              | 58             | 64935                       | 3.63177             | 82.74                 | 20.45     | 15.49      | 24.5                      | 2.6                  | 411884      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision1.v    | 19538                 | 1096                   | 1600              | 100            | 143517                      | 5.61925             | 272.41                | 26.99     | 18.15      | 149.46                    | 15.49                | 676844      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision2.v    | 42078                 | 2534                   | 7396              | 134            | 650583                      | 15.3151             | 3664.98               | 66.72     | 119.26     | 3388.7                    | 62.6                 | 3114880     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision3.v    | 324                   | 55                     | 49                | 30             | 768                         | 2.66429             | 2.25                  | 0.75      | 0.2        | 0.57                      | 0.05                 | 61148       |

**Modified QoR Metrics:**

| arch                                   | circuit            | num_pre_packed_blocks | num_post_packed_blocks | device_grid_tiles | min_chan_width | crit_path_routed_wirelength | critical_path_delay | vtr_flow_elapsed_time | pack_time | place_time | min_chan_width_route_time | crit_path_route_time | max_vpr_mem |
|----------------------------------------|--------------------|-----------------------|------------------------|-------------------|----------------|-----------------------------|---------------------|-----------------------|-----------|------------|---------------------------|----------------------|-------------|
| k6_frac_N10_frac_chain_mem32K_40nm.xml | bgm.v              | 24575                 | 2193                   | 2809              | 82             | 303891                      | 20.414              | 642.01                | 70.09     | 113.58     | 198.09                    | 16.27                | 1222072     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | blob_merge.v       | 11407                 | 684                    | 900               | 72             | 77261                       | 14.6676             | 178.16                | 34.31     | 13.38      | 57.89                     | 3.35                 | 281468      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | boundtop.v         | 1141                  | 369                    | 169               | 40             | 3465                        | 3.5255              | 4.48                  | 1.13      | 0.7        | 0.9                       | 0.17                 | 82912       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | ch_intrinsics.v    | 493                   | 241                    | 100               | 54             | 1424                        | 2.50601             | 1.75                  | 0.19      | 0.27       | 0.43                      | 0.09                 | 60796       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq1.v          | 886                   | 293                    | 256               | 50             | 9972                        | 17.3124             | 15.24                 | 0.69      | 0.97       | 11.27                     | 1.44                 | 72204       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq2.v          | 599                   | 187                    | 256               | 50             | 7621                        | 13.1714             | 14.14                 | 0.63      | 1.04       | 10.93                     | 0.78                 | 68900       |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU8PEEng.v         | 31396                 | 2236                   | 2916              | 98             | 349074                      | 77.8611             | 1269.26               | 88.44     | 153.25     | 843.31                    | 49.13                | 1319276     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU32PEEng.v        | 101542                | 6933                   | 9216              | 176            | 1700697                     | 80.1368             | 28290.01              | 306.21    | 897.95     | 25668.4                   | 278.74               | 4224048     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mcml.v             | 165809                | 6435                   | 8649              | 124            | 1240060                     | 45.6693             | 9384.4                | 296.99    | 686.27     | 4782.43                   | 99.4                 | 4370788     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkDelayWorker32B.v | 4145                  | 1207                   | 2500              | 36             | 33354                       | 8.3986              | 53.94                 | 3.85      | 14.75      | 19.53                     | 2.95                 | 785316      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkPktMerge.v       | 1160                  | 494                    | 784               | 36             | 13881                       | 4.57189             | 20.75                 | 0.82      | 1.97       | 15.01                     | 1.88                 | 117636      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkSMAdapter4B.v    | 2852                  | 529                    | 400               | 56             | 19817                       | 5.21349             | 27.58                 | 5.05      | 2.66       | 14.65                     | 1.11                 | 103060      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | or1200.v           | 4530                  | 1008                   | 729               | 76             | 48034                       | 8.70797             | 202.25                | 10.1      | 8.31       | 171.96                    | 2.86                 | 178712      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | raygentop.v        | 2934                  | 634                    | 361               | 58             | 20799                       | 5.04571             | 22.58                 | 2.75      | 2.42       | 12.86                     | 1.64                 | 108116      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | sha.v              | 3024                  | 236                    | 289               | 62             | 16052                       | 10.5007             | 337.19                | 5.32      | 2.25       | 4.52                      | 0.69                 | 105948      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision0.v    | 21801                 | 1121                   | 1156              | 58             | 70046                       | 3.61684             | 86.5                  | 9.5       | 15.02      | 41.81                     | 2.59                 | 376100      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision1.v    | 19538                 | 1080                   | 1600              | 92             | 142805                      | 6.02319             | 343.83                | 10.68     | 16.21      | 247.99                    | 11.66                | 480352      |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision2.v    | 42078                 | 2416                   | 7396              | 124            | 646793                      | 14.6606             | 5614.79               | 34.81     | 107.66     | 5383.58                   | 62.27                | 2682976     |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision3.v    | 324                   | 54                     | 49                | 34             | 920                         | 2.5281              | 1.55                  | 0.31      | 0.14       | 0.43                      | 0.05                 | 63444       |

Based on these metrics we then calculate the following ratios and summary.

**QoR Metric Ratio** (Modified QoR / Baseline QoR):

| arch                                   | circuit            | num_pre_packed_blocks | num_post_packed_blocks | device_grid_tiles | min_chan_width | crit_path_routed_wirelength | critical_path_delay | vtr_flow_elapsed_time | pack_time | place_time | min_chan_width_route_time | crit_path_route_time | max_vpr_mem |
|----------------------------------------|--------------------|-----------------------|------------------------|-------------------|----------------|-----------------------------|---------------------|-----------------------|-----------|------------|---------------------------|----------------------|-------------|
| k6_frac_N10_frac_chain_mem32K_40nm.xml | bgm.v              | 1.00                  | 0.97                   | 1.00              | 0.98           | 1.02                        | 1.00                | 0.98                  | 0.50      | 1.05       | 1.39                      | 1.04                 | 0.92        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | blob_merge.v       | 1.00                  | 0.98                   | 1.00              | 1.13           | 1.02                        | 0.96                | 0.90                  | 0.51      | 1.18       | 1.22                      | 0.96                 | 0.91        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | boundtop.v         | 1.00                  | 0.95                   | 1.00              | 1.18           | 0.92                        | 0.89                | 0.62                  | 0.44      | 0.85       | 0.43                      | 1.13                 | 0.95        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | ch_intrinsics.v    | 1.00                  | 0.98                   | 1.00              | 1.17           | 0.99                        | 1.02                | 0.68                  | 0.41      | 0.87       | 0.46                      | 1.00                 | 0.97        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq1.v          | 1.00                  | 0.94                   | 1.00              | 0.83           | 1.04                        | 0.96                | 0.98                  | 0.28      | 0.71       | 1.13                      | 1.55                 | 0.83        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | diffeq2.v          | 1.00                  | 0.93                   | 1.00              | 0.96           | 0.85                        | 0.96                | 1.08                  | 0.45      | 1.20       | 1.20                      | 0.83                 | 0.80        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU8PEEng.v         | 1.00                  | 0.98                   | 1.00              | 0.98           | 1.00                        | 0.98                | 0.84                  | 0.50      | 1.00       | 0.84                      | 1.08                 | 0.94        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | LU32PEEng.v        | 1.00                  | 0.96                   | 1.00              | 1.11           | 1.09                        | 1.00                | 1.01                  | 0.49      | 0.96       | 1.02                      | 1.11                 | 0.91        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mcml.v             | 1.00                  | 0.95                   | 1.00              | 0.97           | 0.95                        | 0.89                | 1.03                  | 0.57      | 0.92       | 1.20                      | 0.78                 | 0.87        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkDelayWorker32B.v | 1.00                  | 0.91                   | 1.00              | 0.95           | 1.11                        | 1.00                | 0.82                  | 0.50      | 0.96       | 0.75                      | 0.91                 | 0.98        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkPktMerge.v       | 1.00                  | 0.96                   | 1.00              | 0.82           | 1.04                        | 1.03                | 0.95                  | 0.33      | 0.92       | 1.08                      | 0.96                 | 0.96        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | mkSMAdapter4B.v    | 1.00                  | 0.97                   | 1.00              | 1.17           | 1.03                        | 0.99                | 0.58                  | 0.31      | 0.64       | 0.73                      | 0.97                 | 0.89        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | or1200.v           | 1.00                  | 0.76                   | 1.00              | 1.23           | 0.93                        | 0.90                | 1.91                  | 0.30      | 0.64       | 3.83                      | 0.86                 | 0.81        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | raygentop.v        | 1.00                  | 0.89                   | 1.00              | 1.00           | 0.94                        | 0.98                | 0.57                  | 0.29      | 0.60       | 0.65                      | 0.70                 | 0.86        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | sha.v              | 1.00                  | 1.00                   | 1.00              | 1.00           | 0.96                        | 1.05                | 0.86                  | 0.46      | 0.83       | 0.73                      | 0.92                 | 0.90        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision0.v    | 1.00                  | 1.00                   | 1.00              | 1.00           | 1.08                        | 1.00                | 1.05                  | 0.46      | 0.97       | 1.71                      | 1.00                 | 0.91        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision1.v    | 1.00                  | 0.99                   | 1.00              | 0.92           | 1.00                        | 1.07                | 1.26                  | 0.40      | 0.89       | 1.66                      | 0.75                 | 0.71        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision2.v    | 1.00                  | 0.95                   | 1.00              | 0.93           | 0.99                        | 0.96                | 1.53                  | 0.52      | 0.90       | 1.59                      | 0.99                 | 0.86        |
| k6_frac_N10_frac_chain_mem32K_40nm.xml | stereovision3.v    | 1.00                  | 0.98                   | 1.00              | 1.13           | 1.20                        | 0.95                | 0.69                  | 0.41      | 0.70       | 0.75                      | 1.00                 | 1.04        |
|                                        | GEOMEAN            | 1.00                  | 0.95                   | 1.00              | 1.02           | 1.01                        | 0.98                | 0.92                  | 0.42      | 0.87       | 1.03                      | 0.96                 | 0.89        |

**QoR Summary:**

|                             | baseline | modified |
|-----------------------------|----------|----------|
| num_pre_packed_blocks       | 1.00     | 1.00     |
| num_post_packed_blocks      | 1.00     | 0.95     |
| device_grid_tiles           | 1.00     | 1.00     |
| min_chan_width              | 1.00     | 1.02     |
| crit_path_routed_wirelength | 1.00     | 1.01     |
| critical_path_delay         | 1.00     | 0.98     |
| vtr_flow_elapsed_time       | 1.00     | 0.92     |
| pack_time                   | 1.00     | 0.42     |
| place_time                  | 1.00     | 0.87     |
| min_chan_width_route_time   | 1.00     | 1.03     |
| crit_path_route_time        | 1.00     | 0.96     |
| max_vpr_mem                 | 1.00     | 0.89     |

From the results we can see that our change, on average, achieved a small reduction in the number of logic blocks (0.95) in return for a 2% increase in minimum channel width and 1% increase in routed wirelength. From a run-time persepective the packer is substantially faster (0.42).

### Automated QoR Comparison Script
To automate some of the QoR comparison VTR includes a script to compare pares_resutls.txt files and generate a spreadsheet including the ratio and summary tables.

For example:
```shell
#From the VTR Root
$ ./vtr_flow/scripts/qor_compare.py parse_results1.txt parse_results2.txt parse_results3.txt-o comparison.xlsx
```
will produce ratio tables and a summary table for the files parse_results1.txt, parse_results2.txt and parse_results3.txt, where the first file (parse_results1.txt) is assumed to be the baseline used to produce normalized ratios.

# Adding Tests

Any time you add a feature to VTR you **must** add a test which exercies the feature.
This ensures that regression tests will detect if the feature breaks in the future.

Consider which regression test suite your test should be added to (see [Running Tests](#running-tests) descriptions).

Typically, test which exercise new features should be added to `vtr_reg_strong`.
These tests should use small benchmarks to ensure they:
 * run quickly (so they get run often!), and
 * are easier to debug.
If your test will take more than ~2 mintues it should probably go in a longer running regression test (but see first if you can create a smaller testcase first).

## Adding a test to vtr_reg_strong
This describes adding a test to `vtr_reg_strong`, but the process is similar for the other regression tests.

1. Create a configuration file

    First move to the vtr_reg_strong directory:
    ```shell
    #From the VTR root directory
    $ cd vtr_flow/tasks/regression_tests/vtr_reg_strong
    $ ls
    qor_geomean.txt             strong_flyover_wires        strong_pack_and_place
    strong_analysis_only        strong_fpu_hard_block_arch  strong_power
    strong_bounding_box         strong_fracturable_luts     strong_route_only
    strong_breadth_first        strong_func_formal_flow     strong_scale_delay_budgets
    strong_constant_outputs     strong_func_formal_vpr      strong_sweep_constant_outputs
    strong_custom_grid          strong_global_routing       strong_timing
    strong_custom_pin_locs      strong_manual_annealing     strong_titan
    strong_custom_switch_block  strong_mcnc                 strong_valgrind
    strong_echo_files           strong_minimax_budgets      strong_verify_rr_graph
    strong_fc_abs               strong_multiclock           task_list.txt
    strong_fix_pins_pad_file    strong_no_timing            task_summary
    strong_fix_pins_random      strong_pack
    ```
    Each folder (prefixed with `strong_` in this case) defines a task (sub-test).

    Let's make a new task named `strong_mytest`.
    An easy way is to copy an existing configuration file such as `strong_timing/config/config.txt`
    ```shell
    $ mkdir -p strong_mytest/config
    $ cp strong_timing/config/config.txt strong_mytest/config/.
    ```
    You can now edit `strong_mytest/config/config.txt` to customize your test.

2. Generate golden reference results

    Now we need to test our new test and generate 'golden' reference results.
    These will be used to compare future runs of our test to detect any changes in behaviour (e.g. bugs).

    From the VTR root, we move to the `vtr_flow/tasks` directory, and then run our new test:
    ```shell
    #From the VTR root
    $ cd vtr_flow/tasks
    $ ../scripts/run_vtr_task.pl regression_tests/vtr_reg_strong/strong_mytest

    regression_tests/vtr_reg_strong/strong_mytest
    -----------------------------------------
    Current time: Jan-25 06:51 PM.  Expected runtime of next benchmark: Unknown
    k6_frac_N10_mem32K_40nm/ch_intrinsics...OK
    ```

    Next we can generate the golden reference results using `parse_vtr_task.pl` with the `-create_golden` option:
    ```shell
    $ ../scripts/parse_vtr_task.pl regression_tests/vtr_reg_strong/strong_mytest -create_golden
    ```

    And check that everything matches with `-check_golden`:
    ```shell
    $ ../scripts/parse_vtr_task.pl regression_tests/vtr_reg_strong/strong_mytest -check_golden
    regression_tests/vtr_reg_strong/strong_mytest...[Pass]
    ```

3. Add it to the task list

    We now need to add our new `strong_mytest` task to the task list, so it is run whenever `vtr_reg_strong` is run.
    We do this by adding the line `regression_tests/vtr_reg_strong/strong_mytest` to the end of `vtr_reg_strong`'s `task_list.txt`:
    ```shell
    #From the VTR root directory
    $ vim vtr_flow/tasks/regression_tests/vtr_reg_strong/task_list.txt
    # Add a new line 'regression_tests/vtr_reg_strong/strong_mytest' to the end of the file
    ```

    Now, when we run `vtr_reg_strong`:
    ```shell
    #From the VTR root directory
    $ ./run_reg_test.pl vtr_reg_strong
    #Output trimmed...
    regression_tests/vtr_reg_strong/strong_mytest
    -----------------------------------------
    #Output trimmed...
    ```
    we see our test is run.

4. Commit the new test

    Finally you need to commit your test:
    ```shell
    #Add the config.txt and golden_results.txt for the test
    $ git add vtr_flow/tasks/regression_tests/vtr_reg_strong/strong_mytest/
    #Add the change to the task_list.txt
    $ git add vtr_flow/tasks/regression_tests/vtr_reg_strong/task_list.txt
    #Commit the changes, when pushed the test will automatically be picked up by BuildBot
    $ git commit
    ```

# Debugging Aids
VTR has support for several additional tools/features to aid debugging.

## Sanitizers
VTR can be compiled using *sanitizers* which will detect invalid memory accesses, memory leaks and undefined behaviour (supported by both GCC and LLVM):
```shell
#From the VTR root directory
$ cmake -D VTR_ENABLE_SANITIZE=ON build
$ make
```

## Assertion Levels
VTR supports configurable assertion levels.

The default level (`2`) which turns on most assertions which don't cause significant run-time penalties.

This level can be increased:
```shell
#From the VTR root directory
$ cmake -D VTR_ASSERT_LEVEL=3 build
$ make
```
this turns on more extensive assertion checking and re-builds VTR.

# External Subtrees
VTR includes some code which is developed in external repositories, and is integrated into the VTR source tree using [git subtrees](https://www.atlassian.com/blog/git/alternatives-to-git-submodule-git-subtree).

To simplify the process of working with subtrees we use the `dev/update_external_subtrees.py` script.

For instance, running `./dev/update_external_subtrees.py --list` from the VTR root it shows the subtrees:
```
Component: abc             Path: abc                            URL: https://github.com/berkeley-abc/abc.git       URL_Ref: master
Component: libargparse     Path: libs/EXTERNAL/libargparse      URL: https://github.com/kmurray/libargparse.git    URL_Ref: master
Component: libblifparse    Path: libs/EXTERNAL/libblifparse     URL: https://github.com/kmurray/libblifparse.git   URL_Ref: master
Component: libsdcparse     Path: libs/EXTERNAL/libsdcparse      URL: https://github.com/kmurray/libsdcparse.git    URL_Ref: master
Component: libtatum        Path: libs/EXTERNAL/libtatum         URL: https://github.com/kmurray/tatum.git          URL_Ref: master
```

Code included in VTR by subtrees should *not be modified within the VTR source tree*.
Instead changes should be made in the relevant up-stream repository, and then synced into the VTR tree.

### Updating an existing Subtree
1. From the VTR root run: `./dev/external_subtrees.py $SUBTREE_NAME`, where `$SUBTREE_NAME` is the name of an existing subtree.

    For example to update the `libtatum` subtree:
    ```shell
    ./dev/external_subtrees.py --update libtatum
    ```

### Adding a new Subtree

To add a new external subtree to VTR do the following:

1. Add the subtree specification to `dev/subtree_config.xml`.

    For example to add a subtree name `libfoo` from the `master` branch of `https://github.com/kmurray/libfoo.git` to `libs/EXTERNAL/libfoo` you would add:
    ```xml
    <subtree
        name="libfoo"
        internal_path="libs/EXTERNAL/libfoo"
        external_url="https://github.com/kmurray/libfoo.git"
        default_external_ref="master"/>
    ```
    within the existing `<subtrees>` tag.

    Note that the internal_path directory should not already exist.

    You can confirm it works by running: `dev/external_subtrees.py --list`:
    ```
    Component: abc             Path: abc                            URL: https://github.com/berkeley-abc/abc.git       URL_Ref: master
    Component: libargparse     Path: libs/EXTERNAL/libargparse      URL: https://github.com/kmurray/libargparse.git    URL_Ref: master
    Component: libblifparse    Path: libs/EXTERNAL/libblifparse     URL: https://github.com/kmurray/libblifparse.git   URL_Ref: master
    Component: libsdcparse     Path: libs/EXTERNAL/libsdcparse      URL: https://github.com/kmurray/libsdcparse.git    URL_Ref: master
    Component: libtatum        Path: libs/EXTERNAL/libtatum         URL: https://github.com/kmurray/tatum.git          URL_Ref: master
    Component: libfoo          Path: libs/EXTERNAL/libfoo           URL: https://github.com/kmurray/libfoo.git         URL_Ref: master
    ```
    which shows libfoo is now recognized.

2. Run `./dev/update_external_subtrees.py $SUBTREE_NAME` to add the subtree.

    For the `libfoo` example above this would be:
    ```shell
    ./dev/update_external_subtrees.py libfoo
    ```

    This will create two commits to the repository.
    The first will squash all the upstream changes, the second will merge those changes into the current branch.


### Subtree Rational

VTR uses subtrees to allow easy tracking of upstream dependencies.

Their main advantages included:
 * Works out-of-the-box: no actions needed post checkout to pull in dependencies (e.g. no `git submodule update --init --recursive`)
 * Simplified upstream version tracking
 * Potential for local changes (although in VTR we do not use this to make keeping in sync easier)

See [here](https://blogs.atlassian.com/2013/05/alternatives-to-git-submodule-git-subtree/) for a more detailed discussion.

# Finding Bugs with Coverity
[Coverity Scan](https://scan.coverity.com) is a static code analysis service which can be used to detect bugs.

### Browsing Defects
To view defects detected do the following:

1. Get a coverity scan account

    Contact a project maintainer for an invitation.

2. Browse the existing defects through the coverity web interface


### Submitting a build
To submit a build to coverity do the following:

1. [Download](https://scan.coverity.com/download) the coverity build tool

2. Configure VTR to perform a *debug* build. This ensures that all assertions are enabled, without assertions coverity may report bugs that are gaurded against by assertions. We also set VTR asserts to the highest level.

    ```shell
    #From the VTR root
    mkdir -p build
    cd build
    CC=gcc CXX=g++ cmake -DCMAKE_BUILD_TYPE=debug -DVTR_ASSERT_LEVEL=3 ..
    ```

Note that we explicitly asked for gcc and g++, the coverity build tool defaults to these compilers, and may not like the default 'cc' or 'c++' (even if they are linked to gcc/g++).

3. Run the coverity build tool

    ```shell
    #From the build directory where we ran cmake
    cov-build --dir cov-int make -j8
    ```

4. Archive the output directory

    ```shell
    tar -czvf vtr_coverity.tar.gz cov-int
    ```

5. Submit the archive through the coverity web interface

Once the build has been analyzed you can browse the latest results throught the coverity web interface

### No files emitted
If you get the following warning from cov-build:

    [WARNING] No files were emitted.

You may need to configure coverity to 'know' about your compiler. For example:

    ```shell
    cov-configure --compiler `which gcc-7`
    ```

On unix-like systems run `scan-build make` from the root VTR directory.
to output the html analysis to a specific folder, run `scan-build make -o /some/folder`

# Debugging with clang static analyser
First make sure you have clang installed.
define clang as the default compiler:
  `export CC=clang`
  `export CXX=clang++`

set the build type to `debug` in makefile