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How to Read Combiner Information Files

Acknowledgements: Jonathan Alexander, Actel.

In Designer, the optimizer can perform a variety of functions to remove or combine logic.  Multiple modules can be combined into a single module, for example.   Unneeded logic can be removed.  Logic functions can be optimized by pushing through power and ground connections.  For the applications that do not want combining make sure to attach the preserve attribute onto the Viewlogic net.

For the older version of software, the .cob file contained information on what the Combiner did.  For the newer releases, this file must be exported from the .adb file.   Attached below are samples of the .cob file and how to interpret the codes, letting you know what happened to the modules.

A typical Combiner file looks like this:

**** Header Information*********

DEF PR2_CLK.
USE ; $1I692;
REMOVED:LCOM.
USE ; $1I580;
REMOVED:LCOM.
USE ; $1I895;
REMOVED:TOFF.
USE ; $1I581;
REMOVED:LCOM.
USE ; $1I579;
REMOVED:LCOM.
USE ; $1I690;
REMOVED:LCOM.
USE ; $1I1005/$1I70;
REMOVED:GOB.
USE ; $1I1005/$1I67;
REMOVED:GOB.
USE ; $1I582;
REMOVED:LCOM.
USE ; $1I731;
REMOVED:LCOM.
USE ; $1I721;
REMOVED:LCOM.
USE ; $1I688;
REMOVED:LCOM.
USE ; $1I730;
REMOVED:LCOM.

The following provides a description of the codes used in the Combiner info file:

REMOVED:GOB- The removal of redundant instances.

REMOVED:RCOM- The combining of a Comb gate and a FF (or LATCH). For example, a MX2 gate feeding a FF resulting in a single DFMB.

REMOVED:SPLIT- The split of a DFMB-type into a MUX and a FF. For example, a DFMB is split into a MX2 and a DF1. The MX2 can then be combined with other Comb gates.

REMOVED:TOFF- The removal of constant inputs. For example, a AND3 with 1 input tied to VCC will combine to form an AND2.

REMOVED:FCOM- The simplification of gate with identical inputs. For example, connecting 2 inputs of a AND3 together will combine to an AND2 gate.

REMOVED:LCOM- The combining of two cascading Comb gates. For example a first AND2 feeding only to another AND2 will combine to form a single AND3.

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Last Revised: January 09, 2002
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