Inter-Tile Direct 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:

<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:

<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="<string>": the type of interconnection should be a string. Available types are NONE | column | row, specifies if it applies on a column or a row ot if it doesn’t apply.

x_dir="<string>"

Available directionalities are 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="<string>"

Available directionalities are 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:

<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>

Fig. 28 is the graphical representation of the above scan-chain description on a 4x4 FPGA.

../../../_images/point2point_example.png — Fig. 28 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.

Fig. 29 provides all possible variable combination and the connection it will generate.