Answers Database

MAP: BUFG net attached to a BUF with an X attribute gets distributed using local routing instead of being driven directly by a BUFG


Record #2921

Product Family:  Software

Product Line:  Merged Core

Problem Title:
MAP: BUFG net attached to a BUF with an X attribute gets distributed
using local routing instead of being driven directly by a BUFG



Problem Description:
Keywords:  MAP, net, local, BUFG, BUF

Urgency: Standard

General Description:
Given a net named "PCI_CLK", with an "X" attribute which is driven by a BUF.  Th
e BUF is driven by a BUFG. The intent
is to preserve the net named "PCI_CLK" as the output of
the BUFG, rather than letting it get collapsed and renamed
using the name of the net between the BUFG and the IPAD.
This may be done to preserve a signal name that you can
specify as part of an interface to an IP core macro.

(WEBIMAGE 1: Buffered clock signal isolated with separate BUF symbol)


In XACT:

The BUF element would be collapsed (trimmed out),
but the net would retain the name "PCI_CLK".

In M1 MAP:

The BUF element is not collapsed, and the net "PCI_CLK" ends
up being driven by a CLB and distributed using local routing
instead of being driven directly by the BUFG.

Reference # 11883








Solution 1:

This is mainly a difference in behavior between M1 and XACT.
There is no real workaround that will allow you to keep
the BUF output net name without incurring the additional
function generator delay.




End of Record #2921