Selecting wire_load model in Synopsys DC

[giggs11]

10x10 wire load

hi all,

i'm attempting to run some HDL synthesis on Synopsys DC but am very confused on how to choose the appropriate Wire Load model.

As i understand it, Wire loading models contain all the information required by compiler to estimate interconnect wiring delays.wire load model definition contains: area, resistance,capacitance,slope and fanout. all these attributes are given per unit length wire.

But what is meant by 10x10, 5x5 models....? How do we characterize metal wires and what dimensions do we go by to form wire delay models...? Has the choosing of a model during synthesis got anything to do with die design area...?

If anyone any literature or notes relating to wire load models...please let me know where to obtain online.

Help is much appreciated.

 

[niuniu]

wire_load_from_area

usually the lib will provide some wireload models and an autoselection statement to choose one of them based on the module size. you can let dc autoselect a model.

but in design less than 0.18, wireload model is not accurate, you can choose the smallest wireload at the begining of the synthesis process, or use physical compiler directly.

 

[quake]

when do we use wire_load

Hi. are you using 0.18? if so and your design is large you can choose 30*30, or if you think your design does not have that much load, you can also choose 20*20,
by my experience. tsmc or smic

 

[giggs11]

definition wire_load

hi,

How to specify the wireload autoselect statement in Design Compiler? Can you give the DCSH syntax for the directive...?

Thanks

 

[niuniu]

synopsys load wire model

auto wire load selection is not in script but in the lib file.
not all lib file contain such selection. but you can modify the file by your self.
here is a simple example:

add these lines after wireload model definition in lib file.

wire_load_selection (MY_SEL_ON_AREA) {
wire_load_from_area(0, 10000000, "wl10");
wire_load_from_area(10000000, 20000000, "wl20");
....
}

default_wire_load_mode : enclosed
default_wire_load : wl10
default_wire_load_selection : MY_SEL_ON_AREA

..
for detail information, see SOLD on lib file formation.

 

[quake]

wire load model selection

Yeah, that is it. niuniu is right, you can refer to his script

 

[giggs11]

dc wire load length

hi niuniu,

Appreciate the help. does this mean, with the inclusion of those lines of script, the wire load model doesn't need to be set in DC...?

Thanks.

 

[giggs11]

wire load wl10

hi,

A wire load model of 10x10 may denote a die size of 1mm x 1mm. But my wire load model is stated as :

wire_load("0 to 50"){
....
....
}

wire_load("50 to 100"){
....
....
}

what does "0 to 50" and "50 to 100" denote in terms of die size...?