RAIL Revision Or Appendage Document  (ROAD)


ROAD ID#:      10.1
ISSUE TITLE:   Clarification of net assignments to [Group Nets]
REQUESTER:     Guy de Burgh, Quad Design

DATE SUBMITTED:  February 14, 1997, April 8, 1997
DATE ACCEPTED BY RAIL WORKGROUP:   April 24, 1997

******************************************************************************* 
*******************************************************************************

STATEMENT OF THE ISSUE:
       If a net is allowed to be a member of more than one [Group Nets] it can
       have different [Budgets] to follow as each group will have different
       [Budgets]. This could cause confusion as to which set of [Budgets] the
       net should follow. The same is true about a group being a member of more
       than one [Group Nets]. The RAIL specification needs to clarify this.

*******************************************************************************

STATEMENT OF THE RESOLVED SPECIFICATIONS:

Add to "Other Notes" section of [Group Nets]

|               A net, or group of nets, can be assigned to one group only.
|               This group can become a subgroup of another group to allow
|               for hierarchical net grouping; however, a subgroup can have
|               only one parent group. That is, a subgroup is like a net in
|               that it can be assigned to one group only.
|               A net follows the budgets assigned to the group it is a member
|               of, and for those budgets not defined, the budgets of the
|               hierarchical parent group will be followed. If a budget is
|               defined for both the group and the parent group, then the
|               group budget will be followed, and the parent group budget
|               ignored.

*******************************************************************************

ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:

The question arose when a net was a member of more that one group. Which
set of budgets, assigned to the individual groups, should the net follow?
The RAIL spec. needs to clarify this.
The question was sent to the RAIL reflector and the responses fell into
the following two solutions:

a) A net can be a member of one group only.
b) A net can be a member of multiple groups, and must meet the budgets
   assigned to all the groups it is a member of.

The one net/one group restriction can be circumvented by assigning the
net to a group and then assigning the group to multiple groups. The RAIL
spec. makes no mention of restricting groups in this way.

The RAIL meeting on 27 March 1997 voted unanimously to support a). That is,
a net can be a member of one group only. This was further clarified to
restrict groups such that a subgroup can have only one parent group.

*******************************************************************************

ANY OTHER BACKGROUND INFORMATION:

Question came from Joe Gorman (Viewlogic).


*******************************************************************************