What is Latch based isolation ?

Latch based isolation is similar to latch in architecture.

when user specify  "-clamp_value latch " in set_isolation latch type isolation is used for analysis.

We can mimic RTL behavioural model of latch based isolation as below.


Behavioural model for Latch based isolation :


module ISO_LATCH (data,iso_en,q,VDD,VSS) ;
input data,iso_en;
input VDD,VSS ;  //power and ground pin .
output q;

reg q_latch;


assign q = ((VDD && !VSS )  ? (iso_en ? q_latch : data ) : 1'bx) ;

always @ (VDD,VSS, iso_en,data) begin

  if (!(VDD && !VSS ) ) begin
         q_latch <= 1'bx ;
  end
  else if ( iso_en === 1'bx || iso_en === 1'bz) begin
         q_latch <= 1'bx ;
  end
  else if (iso_en === 1'b1 )
        q_latch <= data ;

end


endmodule

Example:


Let us consider below example to understand the simulation behavior of Latch based isolation.


Design:

module top (input in1,in2,iso_en,output out);

assign out = in1 & in2 ;

endmodule


UPF:

create_power_domain PD1
set_isolation iso_1 -domain PD1 -elements {out} -clamp_value latch  -location self -isolation_signal iso_en -isolation_sense high


Here when "iso_en" signal changes to value 1 , value of signal "out" at that time will be latched until "iso_en" is changes to logic 0 , irrespective of domain primary supply .