- The ``parameter`` and ``localparam`` attributes are used to mark wires
that represent module parameters or localparams (when the HDL front-end
- is run in -pwires mode).
+ is run in ``-pwires`` mode).
+
+- Wires marked with the ``hierconn`` attribute are connected to wires with the
+ same name (format ``cell_name.identifier``) when they are imported from
+ sub-modules by ``flatten``.
- The ``clkbuf_driver`` attribute can be set on an output port of a blackbox
module to mark it as a clock buffer output, and thus prevent ``clkbufmap``
- The ``clkbuf_sink`` attribute can be set on an input port of a module to
request clock buffer insertion by the ``clkbufmap`` pass.
+- The ``clkbuf_inv`` attribute can be set on an output port of a module
+ with the value set to the name of an input port of that module. When
+ the ``clkbufmap`` would otherwise insert a clock buffer on this output,
+ it will instead try inserting the clock buffer on the input port (this
+ is used to implement clock inverter cells that clock buffer insertion
+ will "see through").
+
- The ``clkbuf_inhibit`` is the default attribute to set on a wire to prevent
automatic clock buffer insertion by ``clkbufmap``. This behaviour can be
overridden by providing a custom selection to ``clkbufmap``.
+- The ``invertible_pin`` attribute can be set on a port to mark it as
+ invertible via a cell parameter. The name of the inversion parameter
+ is specified as the value of this attribute. The value of the inversion
+ parameter must be of the same width as the port, with 1 indicating
+ an inverted bit and 0 indicating a non-inverted bit.
+
- The ``iopad_external_pin`` attribute on a blackbox module's port marks
it as the external-facing pin of an I/O pad, and prevents ``iopadmap``
from inserting another pad cell on it.
+- The module attribute ``abc_box_id`` specifies a positive integer linking a
+ blackbox or whitebox definition to a corresponding entry in a `abc9`
+ box-file.
+
+- The port attribute ``abc_carry`` marks the carry-in (if an input port) and
+ carry-out (if output port) ports of a box. This information is necessary for
+ `abc9` to preserve the integrity of carry-chains. Specifying this attribute
+ onto a bus port will affect only its most significant bit.
+
+- The port attribute ``abc_arrival`` specifies an integer (for output ports
+ only) to be used as the arrival time of this sequential port. It can be used,
+ for example, to specify the clk-to-Q delay of a flip-flop for consideration
+ during techmapping.
+
+- The frontend sets attributes ``always_comb``, ``always_latch`` and
+ ``always_ff`` on processes derived from SystemVerilog style always blocks
+ according to the type of the always. These are checked for correctness in
+ ``proc_dlatch``.
+
- In addition to the ``(* ... *)`` attribute syntax, Yosys supports
the non-standard ``{* ... *}`` attribute syntax to set default attributes
for everything that comes after the ``{* ... *}`` statement. (Reset
blackboxes and whiteboxes. Use ``read_verilog -specify`` to enable this
functionality. (By default specify .. endspecify blocks are ignored.)
-- The module attribute ``abc_box_id`` specifies a positive integer linking a
- blackbox or whitebox definition to a corresponding entry in a `abc9`
- box-file.
-
-- The port attribute ``abc_scc_break`` indicates a module input port that will
- be treated as a primary output during `abc9` techmapping. Doing so eliminates
- the possibility of a strongly-connected component (i.e. a combinatorial loop)
- existing. Typically, this is specified for sequential inputs on otherwise
- combinatorial boxes -- for example, applying ``abc_scc_break`` onto the `D`
- port of a LUTRAM cell prevents `abc9` from interpreting any `Q` -> `D` paths
- as a combinatorial loop.
-
-- The port attribute ``abc_carry`` marks the carry-in (if an input port) and
- carry-out (if output port) ports of a box. This information is necessary for
- `abc9` to preserve the integrity of carry-chains. Specifying this attribute
- onto a bus port will affect only its most significant bit.
-
Non-standard or SystemVerilog features for formal verification
==============================================================
into a design with ``read_verilog``, all its packages are available to
SystemVerilog files being read into the same design afterwards.
+- typedefs are supported (including inside packages)
+
- SystemVerilog interfaces (SVIs) are supported. Modports for specifying whether
ports are inputs or outputs are supported.
projects / yosys.git / blobdiff