Testing XOR and XNOR gates with AND/OR inputs

	gate count 1362 number of cells 553 number of library cells 91 number of used cells 38 max fanin 17 max input capacitance 187 max internal fanout 34 critical path 0fF 2280 critical path 6fF 2908
	xaoi21
	xaon21
	xooi21
	xoon21

Now we examine the multiplier netlist to see whether possible new logic gates will be selected by BOOG.

Looking at the netlist with XSCH shows gate combinations like the one below:

The combinations of 2-NOR+2-XOR and 2-AND+2-XOR could be combined into a single gate with 3 inputs. Four gate types like this can be tried out, shown by the symbols above right. In fact, these netlists have already been used as macros in the previous experiments.

Extending an XOR or XNOR gate by turning one of its inputs into a 2-AND or a 2-OR is relatively straight forward. An inverter connected to one of the inputs is changed to a 2-NAND or a 2-NOR gate. Implementing it as a gate netlist is also efficient, since inverting 2-NAND and 2-NOR gates can be used.

The four new cells are added to the list for BOOG. The timing of the xaoi21 and xaon21 gates is made the same as the regular XOR and XNOR gates at 75ps. The timing of the xooi21 and xoon21 gates is set to 100ps, since the input gate structure is slower.

These cells give general benefits in terms of speed, area and connectivity through a reduced number of cells and pin connections. The critical path shows an improvement from 2960 to 2908, or 1.8%; the area improves by 8.0% and the porosity increases by one percentage point from 53% to 54%.

BOOG chooses two of the xaon21, eight of the xoon21 and 102 of the xooi21 cells, which reduces the total number of cells from 666 down to 553.

The conclusion is that these AND/OR into XOR/XNOR gates are useful additions to the library. The critical path is shown below.

               fanout         -- delay--
    x 1          17                  187
 1  nd4v0x1       1  d->z      288   101
 2  oai21v0x2     4  b->z      424   136
 3  iv1v0x4       1  a->z      473    49
 4  oai21v0x2     4  a2->z     612   139
 5  iv1v0x4       1  a->z      661    49
 6  oai21v0x2     4  a2->z     800   139
 7  iv1v0x4       1  a->z      849    49
 8  oai21v0x2     4  a2->z     987   138
 9  iv1v0x4       1  a->z     1036    49
10  oai21v0x2     4  a2->z    1172   136
11  iv1v0x4       1  a->z     1221    49
12  oai21v0x2     4  a2->z    1356   135
13  iv1v0x4       1  a->z     1406    50
14  oai21v0x2     5  a2->z    1572   166
15  xor2v0x1      1  b->z     1685   113
16  xor2v0x2      1  a->z     1796   111
17  xnr2v0x2      1  b->z     1901   105
18  cgi2v0x2      2  b->z     2011   110
19  iv1v0x4       1  a->z     2070    59
20  cgi2v0x2      2  a->z     2182   112
21  iv1v0x4       1  a->z     2232    50
22  cgi2v0x2      2  c->z     2337   105
23  iv1v0x4       1  a->z     2387    50
24  cgi2v0x2      2  c->z     2471    84
25  an2v0x2       2  b->z     2591   120
26  an2v0x2       2  b->z     2737   146
27  xaon21v0x2    0  a1->z    2908   171
    r 15