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  3. AR# 3405: M1.4 Map - Map will sometimes run FLUT to Flop connection through an HLUT routethru.

AR# 3405

M1.4 Map - Map will sometimes run FLUT to Flop connection through an HLUT routethru.

描述

Map will sometimes use an HLUT routhru to make an FLUT
to Flop connection, rather than using a direct connection.
This only happens when two Flops are constrained to a CLB,
but there are no LUTs constrained to the CLB. The result is
unnecessary delay.

解决方案

This problem can be avoided by always constraining associated LUTs
when two flops are constrained to a CLB.

Work Around: Re-mapping the design with the problem .ncd file
as a guide design will cure the problem (it constrains the
LUTs).

Detecting the problem on work station:

Create the following csh script (.scr) and awk script (.awk):

find_hlut.scr:
#!/bin/csh -f
ncdread $1 > /tmp/$1.dmp
cat /tmp/$1.dmp | awk -f find_hlut.awk

find_hlut.awk:
/NC_COMP/ && hlut == "1" && flop == "1" {print "CLB component "comp" has an HLUT route-thru."}
/macinsts/ && hlut == "1" && flop == "1" {print "CLB component "comp" has an HLUT route-thru."}
/NC_COMP/ {comp=$3}
/NC_COMP/ {hlut=0; flop=0}
/H:#LUT:H=F/ {hlut=1}
/H:#LUT:H=G/ {hlut=1}
/DX:H/ {flop=1}
/DY:H/ {flop=1}

To run the script:
find_hlut design.ncd

Sample output:
CLB component <COUNTER.12> has an HLUT route-thru.
CLB component <COUNTER.16> has an HLUT route-thru.
CLB component <COUNTER> has an HLUT route-thru.
CLB component <COUNTER.24> has an HLUT route-thru.
AR# 3405
日期 04/03/2000
状态 Archive
Type 综合文章