File size: 11,091 Bytes
b90fdbb | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 | # Cell Library (Liberty)
OpenTimer reads a set of Cell Library files (.lib)
that contain all cells available to the design.
Each instance declared in the verilog netlist (.v) must have
a corresponding cell type found in the cell library.
+ [Admissible Library Format](#admissible-library-format)
+ [Non-linear Delay Model](#non-linear-delay-model)
# Admissible Library Format
OpenTimer has a built-in parser to read in a library file.
A valid library format contains
1. header section
2. lookup table template definitions
3. cell definitions
A header section has the following syntax.
```text
library (<library name>) {
/* header section */
delay_model : table_lookup ;
time unit : <time unit>
voltage_unit : <voltage unit>
current_unit : <current_unit>
capacitive_load_unit (<float>, <capacitance unit>)
leakage_power_unit : <power unit>
pulling_resistive_unit : <resistance unit>
...
nom_process : <double> ;
nom_temperature : <double> ;
nom_voltage : <double> ;
operating_conditions(<instance name>) {
process : <double> ;
temperature : <double> ;
voltage : <double> ;
}
default_operating_conditions : <instance name>
/* lookup table template definitions */
lu_table_template (<table label>) {
variable_1 : <variable name> ;
index_1 (<string of data points for variable_1>);
variable_2 : <variable name> ;
index_2 (<string of data points for variable_2>);
...
}
... more template definitions
/* cell definitions */
cell (<cell type>) {
pin (<pin name>) {
direction : <direction> ;
clock : <boolean> ;
max_capacitance : <double> ;
min_capacitance : <double> ;
...
timing() {
related_pin : <pin name> ;
/* combinational or sequential definitions */
}
... more timing definitions
}
... more pin definitions
}
... more cell definitions
}
```
## Example
The example below demonstrates a valid library file (source from [TAU15 Contest][TAU15])
for OpenTimer.
```text
library ("simple") {
delay_model : table_lookup ;
time_unit : "1ps" ;
voltage_unit : "1V" ;
current_unit : "1mA" ;
leakage_power_unit : 1uW ;
capacitive_load_unit(1,ff);
pulling_resistance_unit : "1kohm" ;
default_fanout_load : 1.0 ;
default_inout_pin_cap : 0.0 ;
default_input_pin_cap : 0.0 ;
default_output_pin_cap : 0.0 ;
slew_lower_threshold_pct_rise : 20.0 ;
slew_lower_threshold_pct_fall : 20.0 ;
slew_upper_threshold_pct_rise : 80.0 ;
slew_upper_threshold_pct_fall : 80.0 ;
input_threshold_pct_rise : 50.0 ;
input_threshold_pct_fall : 50.0 ;
output_threshold_pct_rise : 50.0 ;
output_threshold_pct_fall : 50.0 ;
nom_voltage : 0.7 ;
nom_temperature : 70.0 ;
nom_process : 1.0 ;
operating_conditions("typical_1.00") {
process : 1.00 ;
temperature : 70.0 ;
voltage : 0.7 ;
tree_type : "balanced_tree" ;
}
default_operating_conditions : "typical_1.00" ;
lu_table_template (delay_outputslew_template_7X8) {
variable_1 : total_output_net_capacitance ;
variable_2 : input_net_transition ;
index_1 ("1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6");
index_2 ("2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7");
}
/* Begin cell: INV_X1 */
cell ("INV_X1") {
pin ("o") {
direction : output ;
capacitance : 0.0 ;
max_capacitance : 12.80 ;
min_capacitance : 0.00 ;
timing() {
cell_fall ("delay_outputslew_template_7X8") {
index_1 ("0.00,1.00,2.00,4.00,8.00,16.00,32.00") ;
index_2 ("5.00,30.00,50.00,80.00,140.00,200.00,300.00,500.00") ;
values (\
"9.376, 14.576, 18.136, 22.088, 27.856, 32.352, 38.568, 48.992",\
"13.544, 18.744, 22.88, 27.96, 35.32, 40.944, 48.52, 60.664",\
"17.704, 22.904, 27.064, 32.992, 41.784, 48.456, 57.336, 71.2",\
"26.04, 31.24, 35.4, 41.64, 52.84, 61.408, 72.68, 89.872",\
"42.704, 47.904, 52.064, 58.304, 70.784, 82.472, 97.92, 121.136",\
"76.04, 81.24, 85.4, 91.64, 104.12, 116.6, 137.272, 170.648",\
"142.704, 147.904, 152.064, 158.304, 170.784, 183.264, 204.064, 245.664"\
);
}
fall_transition ("delay_outputslew_template_7X8") {
index_1 ("0.00,1.00,2.00,4.00,8.00,16.00,32.00") ;
index_2 ("5.00,30.00,50.00,80.00,140.00,200.00,300.00,500.00") ;
values (\
"10, 10.976, 13.104, 16.08, 20.136, 22.92, 26.36, 31.864",\
"15, 15.36, 16.92, 20.224, 25.72, 29.648, 34.384, 41.048",\
"20, 20.072, 21.128, 23.928, 30.376, 35.272, 41.328, 49.488",\
"30, 30, 30.256, 32.08, 38.128, 44.616, 52.912, 64.456",\
"50, 50, 50, 50.32, 54.008, 59.808, 71.024, 88.184",\
"90, 90, 90, 90, 90.448, 93.336, 101.536, 123.584",\
"170, 170, 170, 170, 170, 170, 172.12, 185.672"\
);
}
cell_rise ("delay_outputslew_template_7X8") {
index_1 ("0.00,1.00,2.00,4.00,8.00,16.00,32.00") ;
index_2 ("5.00,30.00,50.00,80.00,140.00,200.00,300.00,500.00") ;
values (\
"9.376, 14.576, 18.136, 22.088, 27.856, 32.352, 38.568, 48.992",\
"13.544, 18.744, 22.88, 27.96, 35.32, 40.944, 48.52, 60.664",\
"17.704, 22.904, 27.064, 32.992, 41.784, 48.456, 57.336, 71.2",\
"26.04, 31.24, 35.4, 41.64, 52.84, 61.408, 72.68, 89.872",\
"42.704, 47.904, 52.064, 58.304, 70.784, 82.472, 97.92, 121.136",\
"76.04, 81.24, 85.4, 91.64, 104.12, 116.6, 137.272, 170.648",\
"142.704, 147.904, 152.064, 158.304, 170.784, 183.264, 204.064, 245.664"\
);
}
rise_transition ("delay_outputslew_template_7X8") {
index_1 ("0.00,1.00,2.00,4.00,8.00,16.00,32.00") ;
index_2 ("5.00,30.00,50.00,80.00,140.00,200.00,300.00,500.00") ;
values (\
"10, 10.976, 13.104, 16.08, 20.136, 22.92, 26.36, 31.864",\
"15, 15.36, 16.92, 20.224, 25.72, 29.648, 34.384, 41.048",\
"20, 20.072, 21.128, 23.928, 30.376, 35.272, 41.328, 49.488",\
"30, 30, 30.256, 32.08, 38.128, 44.616, 52.912, 64.456",\
"50, 50, 50, 50.32, 54.008, 59.808, 71.024, 88.184",\
"90, 90, 90, 90, 90.448, 93.336, 101.536, 123.584",\
"170, 170, 170, 170, 170, 170, 172.12, 185.672"\
);
}
timing_sense : negative_unate ;
related_pin : "a" ;
}
/* End timing */
}
/* End pin */
pin ("a") {
capacitance : 1.00 ;
direction : input ;
}
/* End pin */
}
/* End cell: INV_X1 */
}
```
# Non-linear Delay Model
OpenTimer supports *Non-Linear Delay Model (NLDM)*.
Most of the cell libraries include table models to specify the delays and timing checks
for various timing arcs of the cell.
The table models are referred to as NLDM,
and are used for delay, output slew, and timing tests.
NLDM captures the delay through the combination of input transition time at the cell input pin
and the total output capacitance at the cell output pin.
## How does NLDM Work in OpenTimer?
To give you a better idea about how OpenTimer works with NLDM,
let's start with an example of such a table for a typical inverter cell.
```text
cell ("INV_X1") {
pin ("o") {
direction : output ;
capacitance : 0.0 ;
max_capacitance : 12.80 ;
min_capacitance : 0.00 ;
timing() {
cell_fall ("delay_template_5x5") {
index_1 ("0.00,1.00,2.00,4.00,8.00") ; // input transition
index_2 ("5.00,30.00,50.00,80.00,140.00") ; // output capacitance
values (\
"9.376, 14.576, 18.136, 22.088, 27.856", \
"13.544, 18.744, 22.88, 27.96, 35.32", \
"17.704, 22.904, 27.064, 32.992, 41.784", \
"26.04, 31.24, 35.4, 41.64, 52.84", \
"42.704, 47.904, 52.064, 58.304, 70.784" \
);
}
cell_rise ("delay_template_5x5") {
index_1 ("0.00,1.00,2.00,4.00,8.00") ; // input transition
index_2 ("5.00,30.00,50.00,80.00,140.00") ; // output capacitance
values (\
"9.376, 14.576, 18.136, 22.088, 27.856", \
"13.544, 18.744, 22.88, 27.96, 35.32", \
"17.704, 22.904, 27.064, 32.992, 41.784", \
"26.04, 31.24, 35.4, 41.64, 52.84", \
"42.704, 47.904, 52.064, 58.304, 70.784" \
);
}
timing_sense : negative_unate ;
related_pin : "a" ;
}
}
}
```
The above example describes the delay of from the input pin `a` to the output pin `o`.
Two tables are defined for fall delay and rise delay at pin `o`,
labeled as `cell_fall` and `cell_rise`.
The type of indices and the order of lookup table indices are defined in the
lookup table template `delay_template_5x5`.
```text
lu_table_template(delay_template_5x5) {
variable_1 : input_net_transition;
variable_2 : total_output_net_capacitance;
index_1 ("1000, 1001, 1002");
index_2 ("1000, 1001, 1002");
}
```
This lookup table template defines that the first variable is the input transition time
and the second variable is the output capacitance.
Based on the upon delay tables, an input fall transition time of 1.00 (library time unit)
and an output load of 30.00 (library capacitance unit) will correspond to the rise delay
of the inverter of 18.744 (library time unit).
For values outside the indices, we perform interpolation or extrapolation to obtain the resulting timing values.
## Table Lookup through Linear Interpolation and Extrapolation
The figure below demonstrates different timing lookup tables of scalar,
one dimension, and two dimensions.
<img src="nldm.png" width="70%">
If the table is of size 1x1 (single scalar value),
no interpolation is needed.
Regardless of input `x` and `y`, the output value `z` is constant.
If the table is one-dimensional (1xn or mx1),
the output values depends on the non-scalar dimension.
For instance, in the above 1x4 table, if `y < y1`,
the output value z is the linear extrapolation between `z1` and `z2`.
If `y2 ≤ y ≤ y3`, the output value `z` is the linear interpolation
between `z2` and `z3`.
If `y > y4`, the output value `z` is the linear extrapolation
between `z3` and `z4`.
If the table is two-dimensional,
we perform linear interpolation or extrapolation on the x value first,
and then perform the linear interpolation or extrapolation on the y value.
For instance, in the above 3x4 table,
if `x2 < x < x3` and `y2 < y < y3`,
we compute `z_first` by linear interpolation on `z22` and `z32`,
and `z_second` by linear interpolation on `z23` and `z33`.
Then we determine the output value z by linear interpolation on
`z_first` and `z_second`.
# Reference
1. [2015 ACM TAU Timing Analysis Contest][TAU15]
2. [Synopsys Technology Access Program (TAP-in)][Synopsys TAP-in]
* * *
[Synopsys TAP-in]: https://www.synopsys.com/community/interoperability-programs/tap-in.html
[SDC-Basics]: http://www.vlsi-expert.com/2011/02/synopsys-design-constraints-sdc-basics.html
[TAU15]: https://sites.google.com/site/taucontest2015/
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