For electrical net simulation in SV, I'd like to implement a trapezoidal integration method using companion models for caps and inductors. [http://circsimproj.blogspot.nl/2009/07/companion-models.html]
Some simulation tool vendors provide a SV package allowing to solve for the voltages of a resistive network. See Mixed Signal Verification: Model Development by Simetkosky for a published resolution function.
In order to implement the trapezoidal method, I need to synchronously change equivalent resistors and currents:
- at the beginning of the simulation, a small time step is chosen, every dynamic element is replaced by a resistor.
- the package resolving function calculates new node voltages.
- every dynamic element calculates a maximum time step based on tolerance criteria.
- the next time step is calculated as the minimum of the requested time steps and a (delayed) update signal is issued.
- once the update signal fires, every dynamic element calculates a new equivalent resistance and current..
The package uses a nettype with the following structure:
package SVA_pkg;
typedef struct {
real V;
real I;
real R;
} SVAstruct;
function automatic SVAstruct res_SVA (input SVAstruct driver[]);
// resolution function
endfunction
nettype SVAstruct SVAnet with res_SVA;
endpackage
// in module
inout SVAnet P;
assign P = '{1 , 0 , 0}; // defines a voltage source
In order to find a minimum common time step, delaying and then executing the update of the equivalent resistances and currents I have to pass information around.
This boils down to associate to a SVAnet variables with the following requirements:
- they can be set independently of {V, I, R}
- resolution function for {V, I, R} should not react on them
- no resolution function for them is needed
Clearly, direct extension of SVAstruct would not fulfill the first two requirements.
Ideas?
- Global variables are a possibility, but I would like to see a more automatic way to communicate among connected SVAnets.
- Creating a class or using a substructure on which the resolution works come to my mind but are beyond my programming skills.
