Fatal error found by spectre during topology check.

Please find the attached verilogA code of two modules and help me to solve the error

OK, the issue is that you have indirect branch assignments in the MTJ_model block:

V(mx):
ddt(V(mx)) == k1*(h3*V(my) - h2*V(mz)) + k2*(-h1*V(my)*V(my)- h1*V(mz)*V(mz) + h2*V(mx)*V(my) + h3*V(mx)*V(mz))+k3*net_torque*(-s1*V(my)*V(my) -s1*V(mz)*V(mz) + s2*V(mx)*V(my)+ s3*V(mx)*V(mz));

(similar expressions for my and mz), and then the Initial block has some voltage sources:

V(x) <+ 0.2;//0;

These are in conditional blocks based on the analysis (which is a dubious modelling practice and potentially dangerous because the behaviour might be different). The indirect branch assignments will be creating voltage sources on mx, my and mz - and so the simulator sees these as potentially in parallel. In practice, because of the condition they are not in parallel - the Initial module only has the sources when in the "ic" analysis, and the MTJ module only has the sources when in the "tran" analysis. So you could workaround this by changing the analog begin in the Initial module to:

(* no_rigid_switch_branch *) analog begin

which turns off the check for switch branches (this is sort of a multi-module switch branch).

However I would question whether this is a particularly good way of implementing the model. You might want to look at this again and decide whether there is a better way of setting up the initial conditions. Maybe have the indirect branch assignments there all the time, and use initial conditions in the simulator (which are handled via a 1ohm resistor to avoid the rigid loops) rather than using this Initial block?

Regards,

Andrew

sir, when i tried as per your suggestion by putting the code before analog begin the error report got is attached . please find the attachment error_2.docx

sir, when i tried as per your suggestion by putting the code before analog begin the error report got is attached . please find the attachment error_2.docx

I checked in the same version of Spectre that you're using, and don't see that error. The error you're seeing is exactly what would happen if you have two voltage sources in parallel (the loop of rigid branches that the check normally performs, and that this attribute is disabling). With the attribute on the analog line, no check for a loop of rigid branches is performed, and so parallel voltage sources will lead to a singularity and that's what you're seeing.

I suspect you've changed the conditions in the code so that there is a time when both sources are enabled. For me (because the Initial block as them enabled during the "ic" analysis, and MTJ block has them in "tran" analysis) they are never in parallel at the same time.

Did you change something else as well? Maybe by mistake?

Andrew 

yes sir, i made a small mistake in code. when i remove that transient working. but the output of MTJ is shown  as 

in the graph. it is only 100mv. normally around 1v should be there to indicate high state. any information regarding this . 

Sorry, I can't debug your code for you - I don't know what it's supposed to be doing, and my quick tests showed different (and rather strange behaviour) - the model looks pretty unstable to me.

Andrew