[Docs] add documentation on build verification steps

docs/finn/command_line.rst

@@ -132,6 +132,38 @@ build configuration), and are detailed below.
 
   * ``deploy/`` -- deployment package folder with a bitfile and driver, ready to be copied to target hardware platform
 
+Verification of intermediate steps
+----------------------------------
+
+FINN dataflow builds go through many steps before the bitfile is generated,
+and the flow may produce erronous models due to bugs or unsupported features.
+When running new models throught this process it's a good idea to enable the
+verification features of the dataflow build. In this way, FINN will use the
+input you provide to run through the intermediate models, produce some output
+and compare it against the expected output that you provide.
+
+This is achieved by setting up the following members of the build configuration:
+
+* Set ``verify_steps`` to be a list of :py:mod:`finn.builder.build_dataflow.VerificationStepType`
+  where each element in the list indicates the output of a particular step
+  that will be verified. See the documentation of the ``VerificationStepType``
+  for more information.
+* Set ``verify_input_npy`` to the .npy filename to use as the test input to the
+  verification process. We recommend using a single input example as the
+  verification execution time can be lengthy for rtlsim, especially for larger
+  networks. The shape of the numpy array must match the expected shape by
+  the model.
+* Set ``verify_expected_output_npy`` to the .npy filename to use as the "golden"
+  output that the generated outputs will be compared against. The shape of the
+  numpy array must match the produced output shape of the model.
+
+The output of the verification is twofold:
+
+* A message like ``Verification for folded_hls_cppsim : SUCCESS`` will appear in
+  the build logfile.
+* The output generated by the model at each verified step will be saved as a
+  .npy file under ``verification_output/`` where each file created will indicate
+  the verification step and the result of the verification (FAIL/SUCCESS).
 
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