95 lines
3.8 KiB
ReStructuredText
95 lines
3.8 KiB
ReStructuredText
Interconnection extensions
|
|
==========================
|
|
|
|
This section introduces extensions on the architecture description file about existing interconnection description.
|
|
|
|
Directlist
|
|
----------
|
|
|
|
The original direct connections in the directlist section are documented here_. Its description is given below:
|
|
|
|
.. _here: http://docs.verilogtorouting.org/en/latest/arch/reference/?highlight=directlist#direct-inter-block-connections
|
|
|
|
.. code-block:: xml
|
|
|
|
<directlist>
|
|
<direct name="string" from_pin="string" to_pin="string" x_offset="int" y_offset="int" z_offset="int" switch_name="string"/>
|
|
</directlist>
|
|
|
|
.. note:: These options are required
|
|
|
|
Our extension include three more options:
|
|
|
|
.. code-block:: xml
|
|
|
|
<directlist>
|
|
<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"/>
|
|
</directlist>
|
|
|
|
.. note:: these options are optional. However, if *interconnection_type* is set *x_dir* and *y_dir* are required.
|
|
|
|
* **interconnection_type**: [``NONE`` | ``column`` | ``row``], specifies if it applies on a column or a row ot if it doesn't apply.
|
|
|
|
* **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:
|
|
|
|
* x_dir="positive":
|
|
|
|
* interconnection_type="column": a column will be connected to a column on the **right**, if it exists.
|
|
|
|
* 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.
|
|
|
|
* x_dir="negative":
|
|
|
|
* interconnection_type="column": a column will be connected to a column on the **left**, if it exists.
|
|
|
|
* 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.
|
|
|
|
* **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:
|
|
|
|
* y_dir="positive":
|
|
|
|
* interconnection_type="column": the **bottom** cell of a column will be connected to the next column **top** cell, if it exists.
|
|
|
|
* interconnection_type="row": a row will be connected on an **above** row, if it exists.
|
|
|
|
* y_dir="negative":
|
|
|
|
* interconnection_type="column": the **top** cell of a column will be connected to the next column **bottom** cell, if it exists.
|
|
|
|
* interconnection_type="row": a row will be connected on a row **below**, if it exists.
|
|
|
|
Example
|
|
-------
|
|
|
|
For this example, we will study a scan-chain implementation. The description could be:
|
|
|
|
.. code-block:: xml
|
|
|
|
<directlist>
|
|
<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"/>
|
|
</directlist>
|
|
|
|
:numref:`fig_p2p_exple` is the graphical representation of the above scan-chain description on a 4x4 FPGA.
|
|
|
|
.. _fig_p2p_exple:
|
|
|
|
.. figure:: ./figures/point2point_example.png
|
|
|
|
An example of scan-chain implementation
|
|
|
|
|
|
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.
|
|
|
|
Truth table
|
|
-----------
|
|
|
|
A point to point connection can be applied in different ways than showed in the example section. To help the designer implement his point to point connection, a truth table with our new parameters id provided below.
|
|
|
|
:numref:`fig_p2p_trtable` provides all possible variable combination and the connection it will generate.
|
|
|
|
.. _fig_p2p_trtable:
|
|
|
|
.. figure:: ./figures/point2point_truthtable.png
|
|
|
|
Point to point truth table
|