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.
OpenTimer has a built-in parser to read in a library file. A valid library format contains
- header section
- lookup table template definitions
- cell definitions
A header section has the following syntax.
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
}
The example below demonstrates a valid library file (source from TAU15 Contest) for OpenTimer.
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 */
}
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.
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.
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.
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.
The figure below demonstrates different timing lookup tables of scalar, one dimension, and two dimensions.
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.