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.
Description
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):
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.