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15.2.2 Rule attributes

We propose the following syntax for per-rule attributes:

Rule-attribs are generalized as key-value(s) pairs, which permits the programmer to add arbitrary attributes to the language without adding more keywords to the language. Rule-attrib-lists are just semicolon-delimited lists of one or more rule-attributes. In the case of repeated attributes, the latter pair will override the former. Rule-attribute-lists are optional prefixes to PRS-rules.

For now, the purpose of these attributes is to emit attribute lines suitable for consumption by another text-based tool, such as old versions of prsim. Q: What happens when we OR-combine rules with different attributes?

Some existing attributes:

— Macro: after d

Applies a fixed delay d to a single rule. Affects hflat output and hacprsim operation.

— Macro: after_min d
— Macro: after_max d

Specifies upper and lower bounds on delays for a rule. The upper bound should be greater than or equal to the lower bound, however, this is not checked here.

— Macro: weak b

If b is true (1), rule is considered weak, e.g. feedback, and may be overpowered by non-weak rules. If unspecified, default value is true.

— Macro: W width

Specify the default transistor width for this rule. For uniformly sized stacks, writing this makes the rule much less cluttered than repeating sizes per literal. Widths can always be overridden per literal.

— Macro: L length

Specify the default transistor length for this rule. Lengths can always be overridden per literal.

— Macro: unstab b

If b is true (1), rule is allowed to be unstable, as an exception. If unspecified, default value is true.

— Macro: comb b

If b is true (1), use combinational feedback.

— Macro: iskeeper [b]

If b is true (1), flag that this rule is part of a standard keeper. If unspecified, default value is true.

— Macro: isckeeper [b]

If b is true (1), flag that this rule is part of a combinational feedback keeper. If unspecified, default value is true.

— Macro: diode [b]

If b is true (1), flag that this rule generates a diode-connected transistor. If unspecified, default value is true.

— Macro: res [b]

If b is true (1), flag that this rule is a fake resistor. If unspecified, default value is true.

— Macro: keeper b

For LVS, If b is true (1), staticize (explicitly). This attribute will soon be deprecated in favor of a node attribute autokeeper.

— Macro: hvt
— Macro: lvt
— Macro: svt

If hvt is set, then emit all devices with in this particular rule with hvt (high voltage threshold), unless explicitly overridden in a node literal. If lvt is set, then emit all devices with in this particular rule with lvt (low voltage threshold), unless overridden. svt restores back to standard Vt as the default. When no parameter value is given, implicit value is 1. When multiple settings are given, the last one should take precedence. Default: svt

— Macro: output b

If b is true (1), staticize (explicitly). Q: should this really be a rule-attribute? better off as node-attribute?

— Macro: loadcap C

Use C as load capacitance instead of inferring from configuration.

— Macro: always_random b

If b is true (1), rule delay is based on random exponential distribution. If unspecified, default value is true.

— Macro: N_reff R
— Macro: P_reff R

Use R as effective resistance to override the automatically computed value in other back-end tools. NOTE: This is a hack that should be replaced with a proper implementation of the "fold" expression macro. Consider this attribute deprecated from the start.