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--- config:generic [2025/05/27 18:02] – [Specification directives] rajit
+++ config:generic [2025/05/27 18:12] (current) – [Attributes] rajit
@@ Line 135: / Line 135: @@
 ==== Attributes ====
+ACT supports attributes on both instances and production rules. An ACT instance can be assigned an attribute in the following way:
+<code act>
+bool v @ [attr=0];
+bool w;
+w @ [attr=5];
+</code>
+In these two examples, the signal ''v'' has an attribute called ''attr'' with value ''0'', and signal ''w'' has attribute ''attr'' with value ''5''. These attributes can be inspected by tools. Instead of having a hard-coded set of instance attributes, an ACT configuration file can //specify// the list of supported attributes.
+<code>
+begin act
+string_table instance_attr "i:s:autokeeper" "i:s:iscomb" "i:s:sigtype"
+end
+</code>
+This specifies three instance attributes: ''autokeeper'', ''iscomb'', and ''sigtype''.  In general, an attribute is specified as a string of the form ''//x//://y//://name//''
+  * The first component ''//x//'' can be either ''i'' for an integer attribute, ''b'' for a Boolean attribute, or ''r'' for a real attribute.
+  * The second component ''//y//'' specifies how to unify two attributes (which can happen if two instances with different attributes are connected). Supported methods are
+     * ''s'' : for strict; the two attributes must be equal, otherwise an error is reported.
+     * ''+'' : sum, so the attributes are summed
+     * ''M'' : max, so the maximum value is used
+     * ''m'' : min, so the minimum value is used
+     * ''|'' : or, so a logical OR is used
+     * ''&'': and, so a logical AND is used
+A second set of attributes can be specified per-production rule.
+<code>
+string_table prs_attr "i:s:after" "i:s:keeper" "i:s:iskeeper"
+</code>
+The syntax for these is the same, except the attributes are applied per production rule. These attributes are interpreted by the [[tools:prsim|simulator]] as well as [[tools:netgen|netlist generator]].
+==== Verilog global signal prefix ====
+Since ACT can refer to global signals, this functionality may be needed when converting ACT files into Verilog netlists. Different systems may have different ways that a user can access signals  starting from the top-level in Verilog.
+<code>
+begin act
+  string global_signal_prefix "top."
+end
+</code>
+This specifies that a global signal ''foo'' can be accessed from Verilog using ''top.foo''.