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gate count 1352 number of cells 668 number of library cells 28 number of used cells 18 max fanin 17 max input capacitance 211 max internal fanout 34 critical path 0fF 2754 critical path 6fF 3948 |
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Inverters with a range of drive strengths are added. LOON switches twelve inverters to a higher drive strength with a 0.9% speed improvement at the cost of a 0.7% area increase.
iv1v0x2 71 iv1v0x3 9 iv1v0x12 3 |
The inverter drive strength used by BOOG is x2, and we can see that no weaker drive strengths are subsequently chosen by LOON, indicating that the LOON synthesis more easily can buffer up than buffer down in order to improve speed. The critical path has changed, since the inverter at the start of the previous critical path has now been buffered up to an iv1v0x12.
When we look at the critical path, the cells with the largest delays have a drive strength of x1 with a fanout of 3 or 4. Probably the speed can be improved if these functions were available with a stronger drive strength. This would also allow the inverters between the oai21 cells in the critical path to be buffered up. In this experiment, an inverter drive strength of x2 is the quickest because of the limited drive of the preceeding oai21v0x1 cells.
fanout -- delay--
y 1 16 200
1 aoi22v0x1 1 b2->z 302 102
2 oai21v0x1 4 a2->z 551 249
3 iv1v0x3 1 a->z 600 49
4 oai21v0x1 4 a2->z 849 249
5 iv1v0x3 1 a->z 898 49
6 oai21v0x1 4 a2->z 1147 249
7 iv1v0x3 1 a->z 1196 49
8 oai21v0x1 4 a2->z 1437 241
9 iv1v0x3 1 a->z 1486 49
10 oai21v0x1 4 a2->z 1720 234
11 iv1v0x3 1 a->z 1769 49
12 oai21v0x1 4 a2->z 2003 234
13 iv1v0x3 1 a->z 2052 49
14 oai21v0x1 5 a2->z 2334 282
15 xnr2v0x1 1 b->z 2437 103
16 cgi2v0x1 3 c->z 2620 183
17 iv1v0x3 2 a->z 2682 62
18 iv1v0x2 1 a->z 2741 59
19 nd2v0x2 1 b->z 2801 60
20 oai21v0x1 3 b->z 2975 174
21 xnr2v0x1 1 b->z 3077 102
22 cgi2v0x1 2 c->z 3228 151
23 iv1v0x3 1 a->z 3276 48
24 cgi2v0x1 2 c->z 3408 132
25 an2v0x2 2 b->z 3532 124
26 an2v0x2 2 b->z 3659 127
27 nd2v0x2 1 b->z 3728 69
28 xnr2v0x1 0 b->z 3948 220
r 15 |
| Table of synthesis results | |||||||
| critical path (ps) | gate count | cell count | porosity | library cells | used cells | ||
| synthesis 1 | 4279 | 1561 | 923 | 43% | 9 | 8 | basic inverters, NAND & NOR gates |
| synthesis 2 | 4236 | 1472 | 792 | 45% | 15 | 12 | AND & OR gates |
| synthesis 3 | 4157 | 1357 | 696 | 46% | 19 | 16 | AOI & OAI gates, 2/1 and 2/2 |
| synthesis 4 | 4157 | 1357 | 696 | 46% | 20 | 16 | mxi2 2-way inverting mux |
| synthesis 5 | 3983 | 1343 | 668 | 48% | 21 | 16 | cgi2 carry generator inverting |
| synthesis 6 | 3948 | 1352 | 668 | 48% | 28 | 18 | inverters with multiple drive strengths |
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