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[Doc] Add disclaimer for limitations when using repack pin constraints

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tangxifan 2021-04-21 14:14:54 -06:00
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7
docs/source/manual/file_formats/repack_design_constraints.rst
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@ -3,6 +3,11 @@
Repack Design Constraints (.xml)
--------------------------------
.. warning:: For the best practice, current repack design constraints only support the net remapping between pins in the same port. Pin constraints are **NOT** allowed for two separated ports.
- A legal pin constraint example: when there are two clock nets, ``clk0`` and ``clk1``, pin constraints are forced on two pins in a clock port ``clk[0:2]`` (e.g., ``clk[0] = clk0`` and ``clk[1] == clk1``).
- An **illegal** pin constraint example: when there are two clock nets, ``clk0`` and ``clk1``, pin constraints are forced on two clock ports ``clkA[0]`` and ``clkB[0]`` (e.g., ``clkA[0] = clk0`` and ``clkB[0] == clk1``).
An example of design constraints is shown as follows.
.. code-block:: xml
@ -25,5 +30,5 @@ An example of design constraints is shown as follows.
.. option:: net="<string>"
The net name of the pin to be mapped, which should be consistent with net definition in your ``.blif`` file. The reserved word ``OPEN`` means that no net should be mapped to a given pin. Please ensure that it is not conflicted with any net names in your ``.blif`` file.
.. warning:: Design constraints is a feature for power-users. It may cause repack to fail. It is users's responsibility to ensure proper design constraints