INTRODUCTION.

This document describes a set of when clause definitions and our
interpretation of how they should be mapped to condition existance
and conditional values.

Abbreviations:
   TG := (.lib) timing group
   EC := edge combination (e.g., Rise-to-Rise)

Background:
   Timing groups (TGs) are examined on a per-pin-pair, per-edge combination (EC)
   basis.  All the TGs having the same pin-pair and EC are grouped into a set.
   The mapping logic is based on which of the following three categories describe 
   that set:

         case A:  only default (non-"when") TGs
         case B:  only when (non-"default") TGs
         case C:  at least one default and at least one "when" TG

   For case A, results depend on whether
      . any "when" timing group(s) (for the same pin-pair) exist
         for any OTHER edge-combination.

   For cases B & C, results depend on whether
      . any "when" timing group(s) exist (for the same pin-pair)
         for the SAME edge-combination
      . any "when" timing group(s) exist (for the same pin-pair)
         for any OTHER edge-combination

   By "results depend on", I mean that either the existence condition,
   or the value(s), or both, may change.

TEST CASES

   Note that all of the descriptions that follow apply to a single
   pin-pair combination.

   case A:  only default (non-"when") group(s)

      (1) single, default TG for a given EC
            . should also have default TG for different EC(s), to double-check that
               values are not somehow erroneously commingled
      (2) multiple default TGs, for the same EC
            . value should be the worst case over all the default TGs having the given EC
            . should also have multiple default TGs for different ECs, to double-check that
               values are not somehow erroneously commingled

   case B:  only when (non-"default") group(s)

      (1) single "when" for a given EC (and nothing else for this pin-pair)
      (2) multiple "when" for a given EC (and nothing else for this pin-pair)

      In all cases, arcs should have
         . a conditional value for each "when"
         . a default value equal to the worst case over all TGs having the given EC

   case C:  at least one default and at least one "when" group

      (1) single "when" and single "default" for a given EC (and nothing else for this pin-pair)
      (2) multiple "when" and single "default" for a given EC
      (3) single "when" and multiple "default" for a given EC
      (4) multiple "when" and multiple "default" for a given EC

      In all cases, arcs should have
         . a conditional value for each "when"
         . a default value equal to the worst case over all default TGs having the given EC
               (note that this default differs from that in case (B))