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Types of Delay Models. Delay models Three types of delay models used in Verilog Distributed delay model Lumped Delay model Pin-to-pin (path) Delay model.

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Presentation on theme: "Types of Delay Models. Delay models Three types of delay models used in Verilog Distributed delay model Lumped Delay model Pin-to-pin (path) Delay model."— Presentation transcript:

1 Types of Delay Models

2 Delay models Three types of delay models used in Verilog Distributed delay model Lumped Delay model Pin-to-pin (path) Delay model 1/9/2016 EnhanceEdu, IIIT-H2

3 Distributed Delay Model Delays that are specified on a per element basis Distributed delays a. modelled by assigning delay values - in gate level modelling b. modelled by assigning delays in the continuous assignment - in data flow modelling Provides detailed delay modelling 1/9/2016 EnhanceEdu, IIIT-H3

4 module M (out,a,b,c,d); output out; input a,b,c,d; wire e,f; and #5 a1(e,a,b); and #7 a2(f,c,d); and #4 a3(out,e,f); endmodule module M(out,a,b,c,d); output out; input a,b,c,d; wire e,f; assign #5 e = a & b; assign #7 f = c & d; assign #4 out = e & f; endmodule 1/9/2016 EnhanceEdu, IIIT-H4

5 Lumped delays 1/9/2016 EnhanceEdu, IIIT-H5 Lumped delays are specified on a per module basis. Single delay on the output gate of the module – cumulative delays of all paths is lumped at one location. They are easy to model compared with distributed delays

6 module M (out,a,b,c,d); output out; input a,b,c,d; wire e,f; and a1(e,a,b); and a2(f,c,d); and #11 a3(out,e,f); endmodule module M(out,a,b,c,d); output out; input a,b,c,d; wire e,f; assign e = a & b; assign f = c & d; assign #11 out = e & f; endmodule 1/9/2016 EnhanceEdu, IIIT-H6

7 Pin-to-Pin Delays Delays are assigned individually to paths from each input to each output. Delays can be separately specified for each input/output path. 1/9/2016 EnhanceEdu, IIIT-H7

8 path a-e-out, delay = 9 path b-e-out, delay = 9 path c-f-out, delay = 11 path d-f-out, delay = 11 1/9/2016 EnhanceEdu, IIIT-H8

9 Path Delays Pin-to-Pin delays are named as path delays The delay values got directly from Data Books for standard elements. For larger Digital Circuits, a low level circuit simulator like SPICE may be used. Designer needs to know the I/O pins of the module rather than the internals of the module –so easier to model, even though it is very detailed. 1/9/2016 EnhanceEdu, IIIT-H9

10 Path Delays Distributed Delays and Lumped Delays –already covered. a. Rise, fall, turnoff delays b. Min, max, typ delays We now study Path Delays Specify blocks 1/9/2016 EnhanceEdu, IIIT-H10

11 module M (out,a,b,c,d); output out; input a,b,c,d; wire e,f; specify (a => out) = 9; (b => out) = 9; (c => out) = 11; (d => out) = 11; endspecify and a1(e,a,b); and a2(f,c,d); and a3(out,e,f); endmodule 1/9/2016 EnhanceEdu, IIIT-H11

12 Specify blocks Specify blocks are outside initial and always blocks. Inside specify blocks a. Parallel connections b. Full connections c. Conditional Connections Parallel: If a[3:0] and out[3:0] are 4-bit vectors then, (a => out) = 9 stands for the shorthand of (a[0] => out[0]) = 9; (a[1] => out[1]) = 9; (a[2] => out[2]) = 9; (a[3] => out[3]) = 9; 1/9/2016 EnhanceEdu, IIIT-H12

13 Specify blocks If width does not match for ‘a’ and ‘out’, then it is a illegal connection Full Connection: Here every bit in source field connected to every bit of the destination. A full connection is denoted by *> Example: specify (a,b *> out) = 9; (c,d *> out) = 11; endspecify 1/9/2016 EnhanceEdu, IIIT-H13

14 Conditional Path delays specify if (a) (a => out) = 9; if (~a) (a => out) = 10; if (b & c) (b => out) = 9; if ((c,d) == 2’b01) (c,d *> out) = 11; if ((c,d) != 2’b01) (c,d *> out) = 13; endspecify 1/9/2016 EnhanceEdu, IIIT-H14

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