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# AR# 2443

## Description

General Description:

TIMESPECs that include RAMs in TIMEGRPs show only some or none of the

paths analyzed. This can happen when a Timing Group of RAMs is

infered with the use of a TNM (Time Name).

## Solution

The RAM BEL is typically named by the name of the RAM output NET name.

For example, if the output NET of a ram16x1s is named "N\$1", then the

resulting BEL name for the RAM primitive will also be "N\$1".

For RAM primitives that are deeper than 16 address locations, two

Function Generators are needed to implement the RAM. Each of the FGs

will get a unique BEL name. For example, if the name of the RAM

output NET is "N\$2", then the two BEL names for the RAM will be:

"BEL_N\$2.F" and "BEL_N\$2.G"

If the .ucf file used the following constraints:

TIMEGRP RAMS_B = RAMS(N\$2);

NET N\$32 TNM = RAMS_B;

Then the resulting .pcf file would look like this:

SCHEMATIC START ;

TIMEGRP "RAMS_B" = BEL "N\$2" ;

TS02 = MAXDELAY FROM TIMEGRP "RAMS_B" TO TIMEGRP "RAMPADS" 20 nS ;

SCHEMATIC END ;

The BEL "N\$2" doesn't actually exist, so this TIMEGRP is empty. To

workaround this problem change the TIMEGRP line in the .pcf file to:

TIMEGRP "RAMS_B" = BEL "BEL_N\$2.F" BEL "BEL_N\$2.G" ;

Now the TIMEGRP is valid and the constrinat may be used. One easy way

to find out which are all the RAMs in a design that fit into this

catagory is to do the following:

1. Place th following line in your .ucf file:

TIMEGRP "ALLRAMS" = RAMS ("*") ;

2. Implement the design through MAP and run a verbose TRCE:

trce -v <design_name>

3. Check the trce report file for the BEL names for both the TIMEGRP

to be created and the ALLRAMS TIMEGRP:

Table of Timegroups:

-------------------

TimeGroup RAMS_B:

BELs:

N\$2

TimeGroup ALLRAMS:

BELs:

N\$1 BEL_N\$2.G BEL_N\$2.F

In the above .twr file, N\$2 is the obvious match.

AR# 2443
Date 01/18/2010
Status Archive
Type General Article
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