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.. _fabric_key:
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Fabric Key
~~~~~~~~~~
Fabric key is a secure key for users to generate bitstream for a specific FPGA fabric.
With this key, OpenFPGA can generate correct bitstreams for the FPGA.
Using a wrong key, OpenFPGA may error out or generate wrong bitstreams.
The fabric key support allows users to build secured/classified FPGA chips even with an open-source tool.
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.. figure :: figures/fabric_key_motivation.png
:scale: 60%
:alt: map to buried treasure
The use of fabric key to secure the FPGA chip design
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.. note :: Users are the only owner of the key. OpenFPGA will not store or replicate the key.
Key Generation
`` ` ` ` ` ` ` ` ` ` ` ``
A fabric key can be achieved in the following ways:
- OpenFPGA can auto-generate a fabric key using random algorithms (see detail in :ref: `cmd_build_fabric` )
- Users can craft a fabric key based on auto-generated file by following the file format description.
File Format
`` ` ` ` ` ` ` ` ``
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A fabric key follows an XML format. As shown in the following XML code, the key file includes the organization of configurable blocks in the top-level FPGA fabric.
Configurable Region
^^^^^^^^^^^^^^^^^^^
The top-level FPGA fabric can consist of several configurable regions, where a region may contain one or multiple configurable blocks. Each configurable region can be configured independently and in parrallel.
.. option :: <region id="<int> "/>
- `` id `` indicates the unique id of a configurable region in the fabric.
.. warning :: The id must start from zero!
.. note :: The number of regions defined in the fabric key must be consistent with the number of regions defined in the configuration protocol of architecture description. (See details in :ref: `config_protocol` ).
The following example shows how to define multiple configuration regions in the fabric key.
.. code-block :: xml
<fabric_key>
<region id="0">
<key id="0" name="grid_io_bottom" value="0" alias="grid_io_bottom_1__0_"/>
<key id="1" name="grid_io_right" value="0" alias="grid_io_right_2__1_"/>
<key id="2" name="sb_1__1_" value="0" alias="sb_1__1_"/>
</region>
<region id="1">
<key id="3" name="cbx_1__1_" value="0" alias="cbx_1__1_"/>
<key id="4" name="grid_io_top" value="0" alias="grid_io_top_1__2_"/>
<key id="5" name="sb_0__1_" value="0" alias="sb_0__1_"/>
</region>
<region id="2">
<key id="6" name="sb_0__0_" value="0" alias="sb_0__0_"/>
<key id="7" name="cby_0__1_" value="0" alias="cby_0__1_"/>
<key id="8" name="grid_io_left" value="0" alias="grid_io_left_0__1_"/>
</region>
<region id="3">
<key id="9" name="sb_1__0_" value="0" alias="sb_1__0_"/>
<key id="10" name="cbx_1__0_" value="0" alias="cbx_1__0_"/>
<key id="11" name="cby_1__1_" value="0" alias="cby_1__1_"/>
<key id="12" name="grid_clb" value="0" alias="grid_clb_1__1_"/>
</region>
</fabric_key>
Configurable Block
^^^^^^^^^^^^^^^^^^^
Each configurable block is defined as a key. There are two ways to define a key, either with alias or with name and value.
.. option :: <key id="<int> " alias="<string>" name="<string>" value="<int>"/>
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- `` id `` indicates the sequence of the configurable memory block in the top-level FPGA fabric.
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- `` name `` indicates the module name of the configurable memory block. This property becomes optional when `` alias `` is defined.
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- `` value `` indicates the instance id of the configurable memory block in the top-level FPGA fabric. This property becomes optional when `` alias `` is defined.
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- `` alias `` indicates the instance name of the configurable memory block in the top-level FPGA fabric. If a valid alias is specified, the `` name `` and `` value `` are not required.
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.. warning :: For fast loading of fabric key, strongly recommend to use pairs `` name `` and `` alias `` or `` name `` and `` value `` in the fabric key file. Using only `` alias `` may cause long parsing time for fabric key.
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The following is an example of a fabric key generate by OpenFPGA for a 2 :math: `\times` 2 FPGA.
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This key contains only `` alias `` which is easy to craft.
.. code-block :: xml
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<fabric_key>
<region id="0">
<key id="0" alias="sb_2__2_"/>
<key id="1" alias="grid_clb_2_2"/>
<key id="2" alias="sb_0__1_"/>
<key id="3" alias="cby_0__1_"/>
<key id="4" alias="grid_clb_2_1"/>
<key id="5" alias="grid_io_left_0_1"/>
<key id="6" alias="sb_1__0_"/>
<key id="7" alias="sb_1__1_"/>
<key id="8" alias="cbx_2__1_"/>
<key id="9" alias="cby_1__2_"/>
<key id="10" alias="grid_io_right_3_2"/>
<key id="11" alias="cbx_2__0_"/>
<key id="12" alias="cby_1__1_"/>
<key id="13" alias="grid_io_right_3_1"/>
<key id="14" alias="grid_io_bottom_1_0"/>
<key id="15" alias="cby_2__1_"/>
<key id="16" alias="sb_2__1_"/>
<key id="17" alias="cbx_1__0_"/>
<key id="18" alias="grid_clb_1_2"/>
<key id="19" alias="cbx_1__2_"/>
<key id="20" alias="cbx_2__2_"/>
<key id="21" alias="sb_2__0_"/>
<key id="22" alias="sb_1__2_"/>
<key id="23" alias="cby_0__2_"/>
<key id="24" alias="sb_0__0_"/>
<key id="25" alias="grid_clb_1_1"/>
<key id="26" alias="cby_2__2_"/>
<key id="27" alias="grid_io_top_2_3"/>
<key id="28" alias="sb_0__2_"/>
<key id="29" alias="grid_io_bottom_2_0"/>
<key id="30" alias="cbx_1__1_"/>
<key id="31" alias="grid_io_top_1_3"/>
<key id="32" alias="grid_io_left_0_2"/>
</region>
</fabric_key>
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The following shows another example of a fabric key generate by OpenFPGA for a 2 :math: `\times` 2 FPGA.
This key contains only `` name `` and `` value `` which is fast to parse.
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.. code-block :: xml
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<fabric_key>
<region id="0">
<key id="0" name="sb_2__2_" value="0"/>
<key id="1" name="grid_clb" value="3"/>
<key id="2" name="sb_0__1_" value="0"/>
<key id="3" name="cby_0__1_" value="0"/>
<key id="4" name="grid_clb" value="2"/>
<key id="5" name="grid_io_left" value="0"/>
<key id="6" name="sb_1__0_" value="0"/>
<key id="7" name="sb_1__1_" value="0"/>
<key id="8" name="cbx_1__1_" value="1"/>
<key id="9" name="cby_1__1_" value="1"/>
<key id="10" name="grid_io_right" value="1"/>
<key id="11" name="cbx_1__0_" value="1"/>
<key id="12" name="cby_1__1_" value="0"/>
<key id="13" name="grid_io_right" value="0"/>
<key id="14" name="grid_io_bottom" value="0"/>
<key id="15" name="cby_2__1_" value="0"/>
<key id="16" name="sb_2__1_" value="0"/>
<key id="17" name="cbx_1__0_" value="0"/>
<key id="18" name="grid_clb" value="1"/>
<key id="19" name="cbx_1__2_" value="0"/>
<key id="20" name="cbx_1__2_" value="1"/>
<key id="21" name="sb_2__0_" value="0"/>
<key id="22" name="sb_1__2_" value="0"/>
<key id="23" name="cby_0__1_" value="1"/>
<key id="24" name="sb_0__0_" value="0"/>
<key id="25" name="grid_clb" value="0"/>
<key id="26" name="cby_2__1_" value="1"/>
<key id="27" name="grid_io_top" value="1"/>
<key id="28" name="sb_0__2_" value="0"/>
<key id="29" name="grid_io_bottom" value="1"/>
<key id="30" name="cbx_1__1_" value="0"/>
<key id="31" name="grid_io_top" value="0"/>
<key id="32" name="grid_io_left" value="1"/>
</region>
</fabric_key>
