logic simulation 한양대학교 신현철 교수 [email protected]
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CAD and Design Project Course for SoC
Circuit Simulation (1/2) Real-delay Simulation (Using HSPICE)
V1
V2 Vout2
Vout1
CAD and Design Project Course for SoC
Circuit Simulation (2/2) Zero-delay Simulation (Using ModelSim)
V1
V2 Vout2
Vout1
CAD and Design Project Course for SoC
Logic Simulation (1/3) Digital Logic Circuit Diagram
Boolean Function Y = (A&B) | (!(B&C)&D) Z = (!(B&C)&D) | (!(B&C)&E)
A
B
C
D
E
W1
W2 W3
W4
Y
Z
ISCAS’85 C17 benchmark circuit
CAD and Design Project Course for SoC
Given the boolean function of a net, you can calculate the logic value.
If the circuit size is doubled, the cost for logic simulation will be quadrapled. Recently, the number of CPU gates is over one million.
Ex) Pentium 4 chipset, Altera FPGA, …
Logic Simulation (2/3)
CAD and Design Project Course for SoC
If the boolean function is simplified, logic simulation time becomes shorter. Simplification of boolean function using BDD Simplification of boolean function using Espresso tool Simplification of boolean function using SIS tool
But, if the input vector is changed, all logic values of the nets have to be recalculated. Simulation cost is still high.
If only changed values are calculated, simulation time can be shorter.
Logic Simulation (3/3)
CAD and Design Project Course for SoC
Circuit Data Structure (1/3)
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3
6
2
7
22
23
10
11
19
16
Input Pattern (ISCAS’85 C17 benchmark circuit)
output gate typeinput
10 5 1 3
11 5 3 6
16 5 2 11
19 5 11 7
22 5 10 16
23 5 16 19
** Gate type ** Inverter : 2 AND gate : 3 OR gate : 4 NAND gate : 5 NOR gate: 6 XOR gate: 7 XNOR gate : 8 INPUT PIN : 0 OUTPUT PIN : 1
CAD and Design Project Course for SoC
Circuit Data Structure (2/3)
1
3
6
2
7
NANDGATE
NANDGATE
10
11 NANDGATE
NANDGATE
16
19
NANDGATE
NANDGATE
22
23
1
3
6
2
7
22
23
10
11
19
16
Build Graph
CAD and Design Project Course for SoC
Circuit Data Structure (3/3)
Total switching countSuccessor netPredecessor net
Current logic valuePrevious logic value
LevelNet ID
Gate type
Predecessor net
Predecessor net Successor net
1
3
6
2
7
NANDGATE
NANDGATE
10
11 NANDGATE
NANDGATE
16
19
NANDGATE
NANDGATE
22
23
Vertex Structure
CAD and Design Project Course for SoC
Level Decision Algorithm Pseudo code
Initialize all logic level to 0Current queue = primary inputsWhile (current queue != empty) { for (nets in current queue) { level of gate += 1 if (level of gate is change) next queue <- output net of the gate } if (current queue = empty) { current queue = next queue; next queue = empty }}
CAD and Design Project Course for SoC
Level Decision Algorithm Initialize level to 0 and schedule primary inputs
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
0 0
0
0
0
CAD and Design Project Course for SoC
Level Decision Algorithm Decide level
A
B
C
D
E
W1
W2 W3
W4
Y
Z
1
1 1
1
0
0
A
B
C
D
E
W1
W2 W3
W4
Y
Z
1
1 2
2
3
3
CAD and Design Project Course for SoC
Logic Calculation Algorithm Pseudo code
Initialize all logic valuesSchedule changed primary inputsWhile (schedule != empty) { update nets in order of level for (gates whose outputs are changed) schedule output of the gate}
CAD and Design Project Course for SoC
Logic Calculation Algorithm (1/3) Initialize all logic values
A
B
C
D
E
W1
W2 W3
W4
Y
Z
1
1 0
1
1
1
0
1
0
1
0
CAD and Design Project Course for SoC
Logic Calculation Algorithm (2/3) Calculate logic value
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
1 0
1
1
1
1
0
0
1
0
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
1 0
1
1
1
1
0
0
1
0
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
1 0
1
1
1
1
0
0
1
0
CAD and Design Project Course for SoC
16
Logic Calculation Algorithm (3/3) Calculate switching count
A
B
C
D
E
W1
W2 W3
W4
Y
Z
1 - 0
0
1
1
1
1-1
0-1
1-0
0-1
0-0
1 - 0
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
0
0-1
1-1
11
0
0
1
11
A
B
C
D
E
W1
W2 W3
W4
Y
Z
0
0
1
1
1-1
1
1
1
0
01-0
Level 0 : 3Level 1 : 2
Level 2 : 1 Level 3 : 1
CAD and Design Project Course for SoC
Result Format
You are to print the switching count of each gate and the
total switching count for each
level.
################################################################## RESULT!!! #
#################################################################
####### 0 Level ####### 6 Net's Switchng count : 2 5 Net's Switchng count : 1 4 Net's Switchng count : 2 3 Net's Switchng count : 1 2 Net's Switchng count : 2 1 Net's Switchng count : 1
************************* 0 Level's Total Switching count : 9
####### 1 Level ####### 21 Net's Switchng count : 2 10 Net's Switchng count : 2 9 Net's Switchng count : 0 8 Net's Switchng count : 1 7 Net's Switchng count : 1
************************* 1 Level's Total Switching count : 6
####### 2 Level ####### 17 Net's Switchng count : 2 16 Net's Switchng count : 0 15 Net's Switchng count : 0 14 Net's Switchng count : 0 13 Net's Switchng count : 0 12 Net's Switchng count : 1 11 Net's Switchng count : 1
************************* 2 Level's Total Switching count : 4