93 lines
3.9 KiB
ReStructuredText
93 lines
3.9 KiB
ReStructuredText
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Interconnection extensions
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==========================
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This section will introduce extensions on the architecture description file about existing interconnection description.
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Directlist
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----------
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The original direct connections in the directlist section is doccumented here_. Its description is given below:
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.. _here: http://docs.verilogtorouting.org/en/latest/arch/reference/?highlight=directlist#direct-inter-block-connections
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.. code-block:: xml
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<directlist>
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<direct name="string" from_pin="string" to_pin="string" x_offset="int" y_offset="int" z_offset="int" switch_name="string"/>
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</directlist>
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.. note:: These options are required
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Our extension include three more options:
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.. code-block:: xml
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<directlist>
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<direct name="string" from_pin="string" to_pin="string" x_offset="int" y_offset="int" z_offset="int" switch_name="string" interconnection_type="string" x_dir="string" y_dir="string"/>
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</directlist>
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* **interconnection_type**: [``NONE`` | ``column`` | ``row``], specifies if it applies on a column or a row ot if it doesn't apply. This option is optional and do not need to be set for any direct connection in the direclist. If this option is set *x_dir* and *y_dir* are required.
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* **x_dir**: [``positive`` | ``negative``], specifies if the next cell to connect has a bigger or lower x value. Considering a coordinate system where (0,0) is the origin at the bottom left and *x* and *y* are positives:
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* x_dir="positive":
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* interconnection_type="column": a column will be connected to a column on the **right**, if it exists.
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* interconnection_type="row": the most on the **right** cell from a row connection will connect the most on the **left** cell of next row, if it exists.
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* x_dir="negative":
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* interconnection_type="column": a column will be connected to a column on the **left**, if it exists.
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* interconnection_type="row": the most on the **left** cell from a row connection will connect the most on the **right** cell of next row, if it exists.
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* **y_dir**: [``positive`` | ``negative``], specifies if the next cell to connect has a bigger or lower x value. Considering a coordinate system where (0,0) is the origin at the bottom left and *x* and *y* are positives:
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* y_dir="positive":
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* interconnection_type="column": the **bottom** cell of a column will be connected to the next column **top** cell, if it exists.
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* interconnection_type="row": a row will be connected on an **above** row, if it exists.
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* y_dir="positive":
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* interconnection_type="column": the **top** cell of a column will be connected to the next column **bottom** cell, if it exists.
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* interconnection_type="row": a row will be connected on a row **below**, if it exists.
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Example
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-------
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For this example, we will study a scan-chain implementation.The description could be:
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.. code-block:: xml
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<directlist>
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<direct name="scff_chain" from_pin="clb.sc_out" to_pin="clb.sc_in" x_offset="0" y_offset="-1" z_offset="0" interconnection_type="column" x_dir="positive" y_dir="positive"/>
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</directlist>
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:numref:`fig_p2p_expl` is the graphical representation of the above scan-chain description on a 4x4 FPGA.
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.. _fig_p2p_expl:
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.. figure:: ./figures/point2point_example.png
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:scale: 100%
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:alt: example of scan-chain implementation
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In this figure, the red arrows represent the initial direct connection. The green arrows represent the point to point connection to connect all the columns of CLB together.
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Truth table
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-----------
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A point to point connection can be applied in different ways than showed in the example section. To help the designer implement his own point to point connection, a truth table with our new parameters id provided below.
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:numref:`fig_p2p_trtable` provides all possible variable combination and the connection it will generate.
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.. _fig_p2p_expl:
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.. figure:: ./figures/point2point_truthtable.png
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:scale: 100%
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:alt: point to point truth table
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