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Group abc_* attribute doc with other attributes

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Eddie Hung 2019-08-29 12:13:52 -07:00
parent 3e0f73c3df
commit c52db44f9a
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README.md
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@ -347,6 +347,23 @@ Verilog Attributes and non-standard features
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_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.
- 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
@ -423,23 +440,6 @@ Verilog Attributes and non-standard features
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
==============================================================