-``size="<int>"`` Specify the driving strength of inverter/buffer. For a buffer, the size is the driving strength of the inverter at the second level. Note that we consider a two-level structure for a buffer here.
-``num_level="<int>"`` Define the number of levels of a tapered inverter/buffer. This is required when users need an inverter or a buffer consisting of >2 stages
..note:: For power-gated inverters: all the control signals must be set as ``config_enable`` so that the testbench generation will generate testing waveforms. If the power-gated inverters are auto-generated, all the ``config_enable`` signals must be ``global`` signals as well. If the power-gated inverters come from user-defined netlists, restrictions on ``global`` signals are free.
..note:: For power-gated buffers: all the control signals must be set as ``config_enable`` so that the testbench generation will generate testing waveforms. If the power-gated buffers are auto-generated, all the ``config_enable`` signals must be ``global`` signals as well. If the power-gated buffers come from user-defined netlists, restrictions on ``global`` signals are free.
- f_per_stage is set to 2. As a result, 2nd stage output strength is 4*, the 3rd stage output strength is 16*, and the 4th stage output strength is 64x.
-``topology="transmission_gate|pass_transistor"`` Specify the circuit topology for the pass-gate logic. A transmission gate consists of a *n*-type transistor and a *p*-type transistor. The pass transistor consists of only a *n*-type transistor.
-``nmos_size="<float>"`` the size of *n*-type transistor in a transmission gate or pass_transistor, expressed in terms of the minimum width ``min_width`` defined in the transistor model in :ref:`technology_library`.
-``pmos_size="<float>"`` the size of *p*-type transistor in a transmission gate, expressed in terms of the minimum width ``min_width`` defined in the transistor model in :ref:`technology_library`.
..note:: OpenFPGA does not auto-generate any netlist for SRAM cells. Users should define the HDL modeling in external netlists and ensure consistency to physical designs.
..note:: The circuit designs of SRAMs are highly dependent on the technology node and well optimized by engineers. Therefore, FPGA-Verilog/SPICE requires users to provide their customized SRAM Verilog/SPICE/Verilog netlists. A sample Verilog/SPICE netlist of SRAM can be found in the directory SpiceNetlists in the released package. FPGA-Verilog/SPICE assumes that all the LUTs and MUXes employ the SRAM circuit design. Therefore, currently only one SRAM type is allowed to be defined.
..note:: The information of input and output buffer should be clearly specified according to the customized Verilog/SPICE netlist! The existence of input/output buffers will influence the decision in creating testbenches, which may leads to larger errors in power analysis.
..note:: OpenFPGA always assume that a ``WL`` port should be the write enable signal, a ``WLR`` port should be the read enable signal, while a ``BL`` port is the data input.
..note:: When the ``memory_bank`` type of configuration procotol is specified, SRAM modules should have a BL and a WL. WLR is optional
..note:: OpenFPGA always assume that a ``WL`` port should be the write/read enable signal, while a ``BL`` port is the data input.
..note:: When the ``frame_based`` type of configuration procotol is specified, the configurable latch or a SRAM with ``BL`` and ``WL`` should be specified.
The circuit model in the type of ``gate`` aims to support direct mapping to standard cells or customized cells provided by technology vendors or users.
-``topology="AND|OR|MUX2"`` Specify the logic functionality of a gate. As for standard cells, the size of each port is limited to 1. Currently, only 2-input and single-output logic gates are supported.
- A 2-input MUX gate with two inputs ``in0`` and ``in1``, a select port ``sel`` and an output port ``out``
- The Verilog of MUX2 gate is provided by the user in the netlist ``sc_mux.v``
- The use of ``lib_name`` to bind to a Verilog module with different port names.
- When binding to the Verilog module, the inputs will be swapped. In other words, ``in0`` of the circuit model will be wired to the input ``B`` of the MUX2 cell, while ``in1`` of the circuit model will be wired to the input ``A`` of the MUX2 cell.
..note:: OpenFPGA requires a fixed truth table for the ``MUX2`` gate. When the select signal sel is enabled, the first input, i.e., ``in0``, will be propagated to the output, i.e., ``out``. If your standard cell provider does not offer the exact truth table, you can simply swap the inputs as shown in the example.
-``structure="tree|multi-level|one-level"`` Specify the multiplexer structure for a multiplexer. The structure option is only valid for SRAM-based multiplexers. For RRAM-based multiplexers, currently we only support the one-level structure
-``add_const_input="true|false"`` Specify if an extra input should be added to the multiplexer circuits. For example, an 4-input multiplexer will be turned to a 5-input multiplexer. The extra input will be wired to a constant value, which can be specified through the XML syntax ``const_input_val``.
-``const_input_val="0|1"`` Specify the constant value, to which the extra input will be connected. By default it is 0. This syntax is only valid when the ``add_const_input`` is set to true.
-``local_encoder="true|false"``. Specify if a local encoder should be added to the multiplexer circuits. The local encoder will interface the SRAM inputs of multiplexing structure and SRAMs. It can encode the one-hot codes (that drive the select port of multiplexing structure) to a binary code. For example, 8-bit ``00000001`` will be encoded to 3-bit ``000``. This will help reduce the number of SRAM cells used in FPGAs as well as configuration time (especially for scan-chain configuration protocols). But it may cost an area overhead.
..note:: For tree-like multiplexers, they can be built with standard cell MUX2. To enable this, users should define a ``circuit_model``, which describes a 2-input multiplexer (See details and examples in how to define a logic gate using ``circuit_model``. In this case, the ``circuit_model_name`` in the ``pass_gate_logic`` should be the name of MUX2 ``circuit_model``.
:numref:`fig_mux1` illustrates an example of multiplexer modelling, which consists of input/output buffers and a transmission-gate-based tree structure.
.._fig_mux1:
..figure:: ./figures/mux1lvl.png
:scale:60%
:alt:Detailed one level Multiplexer
An example of a one level multiplexer with transistor-level design parameters
:numref:`fig_mux` illustrates an example of multiplexer modelling, which consists of input/output buffers and a transmission-gate-based tree structure.
.._fig_mux:
..figure:: ./figures/mux.png
:scale:100%
:alt:Examples of Mux-tree
An example of a tree-like multiplexer with transistor-level design parameters
If we arbitrarily fix the number of Mux entries at 4, the following code could illustrate (a):
The auto-generated LUTs are based on a tree-like multiplexer, whose gates of the transistors are used as the inputs of LUTs and the drains/sources of the transistors are used for configurable memories (SRAMs).
..note:: In the context of LUT, ``input_buffer`` corresponds to the buffer for the datapath inputs of multiplexers inside a LUT. ``lut_input_buffer`` corresponds to the buffer at the inputs of a LUT
-``location_map="[1|-]"`` Customize the location of buffers in intermediate stages. Users can define an integer array consisting of '1' and '-'. Take the example in :numref:`fig_lut_intermediate_buffer_example`, ``-1-`` indicates buffer inseration to the second stage of the LUT multiplexer tree, considering a 3-input LUT.
..note:: For a LUT, three types of ports (``input``, ``output`` and ``sram``) should be defined. If the user provides an customized Verilog/SPICE netlist, the bandwidth of ports should be defined to the same as the Verilog/SPICE netlist. To support customizable LUTs, each type of port contain special keywords.
-``tri_state_map="[-|1]"`` Customize which inputs are fixed to constant values when the LUT is in fracturable modes. For example, ``tri_state_map="----11"`` indicates that the last two inputs will be fixed to be logic '1' when a 6-input LUT is in fracturable modes.
-``circuit_model_name="<string>"`` Specify the circuit model to build logic gates in order to tri-state the inputs in fracturable LUT modes. It is required to use an ``AND`` gate to force logic '0' or an ``OR`` gate to force logic '1' for the input ports.
-``is_harden_lut_port="[true|false]"`` Specify if the input drives a harden logic inside a LUT. A harden input is supposed **NOT** to drive any multiplexer input (the internal multiplexer of LUT). As a result, such inputs are not considered to implement any truth table mapped to the LUT. If enabled, the input will **NOT** be considered for wiring to internal multiplexers as well as bitstream generation. By default, an input port is treated **NOT** to be a harden LUT port.
-``lut_frac_level="<int>"`` Specify the level in LUT multiplexer tree where the output port are wired to. For example, ``lut_frac_level="4"`` in a fracturable LUT6 means that the output are potentially wired to the 4th stage of a LUT multiplexer and it is an output of a LUT4.
-``lut_output_mask="<int>"`` Describe which fracturable outputs are used. For instance, in a 6-LUT, there are potentially four LUT4 outputs can be wired out. ``lut_output_mask="0,2"`` indicates that only the first and the thrid LUT4 outputs will be used in fracturable mode.
-``is_harden_lut_port="[true|false]"`` Specify if the output is driven by a harden logic inside a LUT. A harden input is supposed **NOT** to be driven by any multiplexer output (the internal multiplexer of LUT). As a result, such outputs are not considered to implement any truth table mapped to the LUT. If enabled, the output will **NOT** be considered for wiring to internal multiplexers as well as bitstream generation. By default, an output port is treated **NOT** to be a harden LUT port.
-``mode_select="true|false"`` Specify if this port is used to switch the LUT between different operating modes, the SRAM bits of a fracturable LUT consists of two parts: configuration memory and mode selecting.
-``circuit_model_name="<string>"`` Specify the circuit model to be drive the SRAM port. Typically, the circuit model should be in the type of ``ccff`` or ``sram``.
-``default_val="0|1"`` Specify the default value for the SRAM port. The default value will be used in generating testbenches for unused LUTs
..note:: The size of a mode-selection SRAM port should be consistent to the number of '1s' or '0s' in the ``tri_state_map``.
:numref:`fig_single_lut3_example` illustrates an example of LUT modeling, which consists of input/output buffers and a transmission-gate-based tree structure.
:numref:`fig_frac_lut3_example` illustrates a typical example of 3-input fracturable LUT modeling, which consists of input/output buffers and a transmission-gate-based tree structure.
:numref:`fig_std_frac_lut` illustrates the detailed schematic of a standard fracturable 6-input LUT, where the 5th and 6th inputs can be pull up/down to a fixed logic value to enable LUT4 and LUT5 outputs.
.._fig_std_frac_lut:
..figure:: ./figures/std_frac_lut.svg
:scale:80%
:alt:detailed lut composition
Detailed schematic of a standard fracturable 6-input LUT.
- Fracturable 6-input LUT which is configurable by 66 SRAM cells.
- There are two SRAM cells to switch the operating mode of this LUT, configured by two configuration-chain flip-flops ``ccff``
- The inputs ``in[4]`` and ``in[5]`` of LUT will be tri-stated in dual-LUT4 and dual-LUT5 modes respectively.
- An 2-input OR gate will be wired to the inputs ``in[4]`` and ``in[5]`` to tri-state them. The mode-select SRAM will be wired to an input of the OR gate.
- There will be two outputs wired to the 4th stage of routing multiplexer (the outputs of dual 4-input LUTs)
- By default, the mode-selection configuration bit will be '11', indicating that by default the LUT will operate in dual-LUT4 mode.
Native Fracturable LUT
``````````````````````
:numref:`fig_native_frac_lut` illustrates the detailed schematic of a native fracturable 6-input LUT, where LUT4, LUT5 and LUT6 outputs are always active and there are no tri-state buffers.
.._fig_native_frac_lut:
..figure:: ./figures/native_frac_lut.svg
:scale:80%
:alt:detailed lut composition
Detailed schematic of a native fracturable 6-input LUT.
:numref:`fig_lut_arith` illustrates the detailed schematic of a fracturable 4-input LUT coupled with carry logic gates. For fracturable LUT schematic, please refer to :numref:`fig_std_frac_lut`.
This feature allows users to fully customize their LUT circuit implementation while being compatible with OpenFPGA's bitstream generator when mapping truth tables to the LUTs.
..warning:: OpenFPGA does **NOT** support netlist autogeneration for the LUT with harden logic. Users should build their own netlist and use ``verilog_netlist`` syntax of :ref:`circuit_library` to include it.
.._fig_lut_arith:
..figure:: ./figures/lut_arith_example.svg
:scale:80%
:alt:detailed lut composition
Detailed schematic of a fracturable 4-input LUT with embedded carry logic.
- Fracturable 4-input LUT which is configurable by 16 SRAM cells.
- There are two output wired to the 3th stage of routing multiplexer (the outputs of dual 3-input LUTs)
- There are two outputs wired to the 2th stage of routing multiplexer (the outputs of 2-input LUTs in the in the lower part of SRAM cells). Note that the two outputs drive the embedded carry logic
- There is a harden carry logic, i.e., a 2-input MUX, to implement high-performance carry function.
- There is a mode-switch multiplexer at ``cin`` port, which is used to switch between arithemetic mode and regular LUT mode.
..note:: If the embedded harden logic are driven partially by LUT outputs, users may use the :ref:`file_formats_bitstream_setting` to gaurantee correct bitstream generation for the LUTs.
..note:: OpenFPGA does not auto-generate any netlist for datapath flip-flops. Users should define the HDL modeling in external netlists and ensure consistency to physical designs.
..note:: The circuit designs of flip-flops are highly dependent on the technology node and well optimized by engineers. Therefore, FPGA-Verilog/SPICE requires users to provide their customized FF Verilog/SPICE/Verilog netlists. A sample Verilog/SPICE netlist of FF can be found in the directory SpiceNetlists in the released package.
The information of input and output buffer should be clearly specified according to the customized SPICE netlist! The existence of input/output buffers will influence the decision in creating SPICE testbenches, which may leads to larger errors in power analysis.
..note:: FPGA-Verilog/SPICE currently support only one clock domain in the FPGA. Therefore there should be only one clock port to be defined and the size of the clock port should be 1.
- A regular flip-flop which is defined in a Verilog netlist ``ff.v`` and a SPICE netlist ``ff.sp``
- The flip-flop has ``set`` and ``reset`` functionalities
- The flip-flop port names defined differently in standard cell library and VPR architecture. The ``lib_name`` capture the port name defined in standard cells, while ``prefix`` capture the port name defined in ``pb_type`` of VPR architecture file
- A multi-mode flip-flop which is defined in a Verilog netlist ``frac_ff.v`` and a SPICE netlist ``frac_ff.sp``
- The flip-flop has a ``reset`` pin which can be either active-low or active-high, depending on the mode selection pin ``MODE``.
- The mode-selection bit will be generated by a configurable memory outside the flip-flop, which will be implemented by a circuit model ``CCFF`` defined by users (see an example in :ref:`circuit_model_ccff_example`).
- The flip-flop port names defined differently in standard cell library and VPR architecture. The ``lib_name`` capture the port name defined in standard cells, while ``prefix`` capture the port name defined in ``pb_type`` of VPR architecture file
..note:: OpenFPGA does not auto-generate any netlist for configuration chain flip-flops. Users should define the HDL modeling in external netlists and ensure consistency to physical designs.
..note:: The circuit designs of configurable memory elements are highly dependent on the technology node and well optimized by engineers. Therefore, FPGA-Verilog/SPICE requires users to provide their customized FF Verilog/SPICE/Verilog netlists. A sample Verilog/SPICE netlist of FF can be found in the directory SpiceNetlists in the released package.
The information of input and output buffer should be clearly specified according to the customized SPICE netlist! The existence of input/output buffers will influence the decision in creating SPICE testbenches, which may leads to larger errors in power analysis.
..note:: FPGA-Verilog/SPICE currently support only one clock domain for any configuration protocols in the FPGA. Therefore there should be only one clock port to be defined and the size of the clock port should be 1.
..note:: A flip-flop should at least have three types of ports, ``input``, ``output`` and ``clock``.
..note:: If the user provides a customized Verilog/SPICE netlist, the bandwidth of ports should be defined to the same as the Verilog/SPICE netlist.
..note:: In a valid FPGA architecture, users should provide at least either a ``ccff`` or ``sram`` circuit model, so that the configurations can loaded to core logic.
..note:: OpenFPGA does not auto-generate any netlist for the hard logics. Users should define the HDL modeling in external netlists and ensure consistency to physical designs.
..note:: The information of input and output buffer should be clearly specified according to the customized Verilog/SPICE netlist! The existence of input/output buffers will influence the decision in creating SPICE testbenches, which may leads to larger errors in power analysis.
- A multi-mode 8-bit multiplier which is defined in a Verilog netlist ``dsp.v`` and a SPICE netlist ``dsp.sp``
- The multi-mode multiplier can operating in two modes: (1) dual 4-bit multipliers; and (2) 8-bit multiplier
- The mode-selection bit will be generated by a configurable memory outside the flip-flop, which will be implemented by a circuit model ``CCFF`` defined by users (see an example in :ref:`circuit_model_ccff_example`).
- A 128x8 dual port RAM which is defined in a Verilog netlist ``dpram.v`` and a SPICE netlist ``dpram.sp``
- The clock port of the RAM is controlled by a global signal (see details about global signal definition in :ref:`annotate_vpr_arch_physical_tile_annotation`).
- A fracturable dual port RAM which is defined in a Verilog netlist ``frac_dpram.v`` and a SPICE netlist ``frac_dpram.sp``
- The dual port RAM can operate in two modes: (1) 128 addresses with 8-bit data width; (2) 256 addresses with 4-bit data width
- The clock port of the RAM is controlled by a global signal (see details about global signal definition in :ref:`annotate_vpr_arch_physical_tile_annotation`).
- The mode-selection bit will be generated by a configurable memory outside the flip-flop, which will be implemented by a circuit model ``CCFF`` defined by users (see an example in :ref:`circuit_model_ccff_example`).
FPGA architecture requires two type of wire segments:
-``wire``, which targets the local wires inside the logic blocks. The wire has one input and one output, directly connecting the output of a driver and the input of the downstream unit, respectively
-``chan_wire``, especially targeting the channel wires. The channel wires have one input and two outputs, one of which is connected to the inputs of Connection Boxes while the other is connected to the inputs of Switch Boxes. Two outputs are created because from the view of layout, the inputs of Connection Boxes are typically connected to the middle point of channel wires, which has less parasitic resistances and capacitances than connected to the ending point.
..note:: FPGA-Verilog/SPICE can auto-generate the Verilog/SPICE model for wires while also allows users to provide their customized Verilog/SPICE netlists.
..note:: The information of input and output buffer should be clearly specified according to the customized netlist! The existence of input/output buffers will influence the decision in creating testbenches, which may leads to larger errors in power analysis.
-``model_type="pi|T"`` Specify the type of RC models for this wire segement. Currently, OpenFPGA supports the :math:`\pi`-type and T-type multi-level RC models.
- The routing wire will be modelled as a 1-level :math:`\pi`-type RC wire model with a total resistance of :math:`103.84\Omega` and a total capacitance of :math:`13.89fF`
..note:: OpenFPGA does not auto-generate any netlist for I/O cells. Users should define the HDL modeling in external netlists and ensure consistency to physical designs.
Therefore, FPGA-Verilog/SPICE requires users to provide their customized Verilog/SPICE/Verilog netlists. A sample Verilog/SPICE netlist of an I/O pad can be found in the directory SpiceNetlists in the released package.
..note:: The information of input and output buffer should be clearly specified according to the customized netlist! The existence of input/output buffers will influence the decision in creating testbenches, which may leads to larger errors in power analysis.
