Issue with pre-packing. The tool doesn't find the pairs.

[GoogleCodeExporter]

Hello,

In VPR 7 when output of the LUT goes through a latch, the CAD tool merges the 
pair in the same LB, even you do not use advanced pre-packing option.

I use simple Hard-Logics (HL) beside LUTs in my architecture, but the tool 
fails to find the HL-latch pairs and puts them in separate LBs. Actually, it 
routes the HL's output through another LUT (so dedicates an extra intermediate 
LUT), then connects the LUT's output to the latch (which is in the LB of 
intermediate LUT)! Thus, it imposes area and delay overhead.

To solve this issue, I defined pre-packing by using "pack_pattern" for the LUT, 
HL1 and HL2. However, the tools hangs in initial step, after printing "Begin 
prepacking".

The architecture and a simple blif file is attached. You may find the 3 
pre-packing specifications by searching pack_pattern in the arch file. Thanks 
in advance.

Best regards,
Behnam Khaleghi

Original issue reported on code.google.com by behnam5...@gmail.com on 30 Dec 2014 at 6:07

Attachments:

• [arch and blif.zip](https://storage.googleapis.com/google-code-attachments/vtr-verilog-to-routing/issue-99/comment-0/arch and blif.zip)

[GoogleCodeExporter]

When identifying pack patterns, you need to mark every interconnect along the 
path that joins two blocks that you want to keep together.  So if you have 
HL1_perm --> [wire1] --> [wire2] --> FF then both wire1 and wire 2 need to be 
labelled with same pack_pattern.  For your architecture, this means line 211:

<pack_pattern name="ble2" in_port="logic.out" out_port="ff.D"/>

implies that you need to add a pack_pattern on line 204:

<pack_pattern name="ble2" in_port="perm.out" out_port="logic.out"/>

Our original plan behind pack patterns was to automatically identify them and 
use manual identification as an intermediate step towards that goal.  But I've 
graduated before getting around to that.  So I'll apologize now for the very 
manual process of identifying these things.

Original comment by JasonKai...@gmail.com on 2 Jan 2015 at 2:15

[GoogleCodeExporter]

Thanks Dr. Luu. It really helped us.

Original comment by behnam5...@gmail.com on 2 Jan 2015 at 5:28