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Update README.md for (* abc9_required *)

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Eddie Hung 2020-01-15 14:42:00 -08:00
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@ -373,10 +373,15 @@ Verilog Attributes and non-standard features
`abc9` to preserve the integrity of carry-chains. Specifying this attribute `abc9` to preserve the integrity of carry-chains. Specifying this attribute
onto a bus port will affect only its most significant bit. onto a bus port will affect only its most significant bit.
- The port attribute ``abc9_arrival`` specifies an integer (for output ports - The output port attribute ``abc9_arrival`` specifies an integer, or a string
only) to be used as the arrival time of this sequential port. It can be used, of space-separated integers to be used as the arrival time of this blackbox
for example, to specify the clk-to-Q delay of a flip-flop for consideration port. It can be used, for example, to specify the clk-to-Q delay of a flip-
during `abc9` techmapping. flop output for consideration during `abc9` techmapping.
- The input port attribute ``abc9_requiredl`` specifies an integer, or a string
of space-separated integers to be used as the required time of this blackbox
port. It can be used, for example, to specify the setup-time of a flip-flop
input for consideration during `abc9` techmapping.
- The module attribute ``abc9_flop`` is a boolean marking the module as a - The module attribute ``abc9_flop`` is a boolean marking the module as a
flip-flop. This allows `abc9` to analyse its contents in order to perform flip-flop. This allows `abc9` to analyse its contents in order to perform