Hi,
As a beginner for learning verilog-A, I got a syntax error when I tried to implement 4-bit lookup table with a case statement. I couldn't figure out why Synopsys hspice 2005 complains my code "lookup.va" with the following errors. Is anyone suggesting me the reason or the simple way to implement 4-bit lookup table?
Any comments would be welcome.

Yongjin CHOI

                  hsp-vacomp: Synopsys HSPICE Verilog-A Compiler Version 1.26.111705.
                  hsp-vacomp: Copyright (C) 2005 Synopsys, Inc. All Rights Reserved.
                  hsp-vacomp:
                  hsp-vacomp: Error: Missing array index in using 'result'.
                  hsp-vacomp:    ['lookup.va',30]

                 ** error **
                 During Verilog-A Device processing:
                 Failed to compile the Verilog-A File, 'lookup.va'.

// Simple Lookup table 'lookup.va'

`include "disciplines.vams"
`include "constants.vams"

module lookup(out,in);
  parameter real vdd = 2.5;
  parameter real thresh = vdd/2;
  parameter real tt=0.1n from (0:inf); // transition time of output signal
  parameter real td=0 from (0:inf); // average delay from input to output

  input [0:3] in;
  output [0:3] out;

  electrical [0:3] in;
  electrical [0:3] out;
  integer result [0:3];
  real vout [0:3];
  genvar i;

  analog begin
     for (i=0; i < 4; i=i+1) begin
       if(V(in[i]) >= thresh) begin
               result[i]= 1;
       end else begin
               result[i]=0;
       end
     end //for

    case(result)
       4'b0000 : begin vout[0]= 3; vout[1]= 0; vout[2]= 0; vout[3]= 0; end
       4'b0001 : begin vout[0]= 0; vout[1]= 3; vout[2]= 0; vout[3]= 0; end
       4'b0010 : begin vout[0]= 0; vout[1]= 0; vout[2]= 3; vout[3]= 0; end
       4'b0011 : begin vout[0]= 0; vout[1]= 0; vout[2]= 0; vout[3]= 3; end
       4'b0100 : begin vout[0]= 1; vout[1]= 0; vout[2]= 0; vout[3]= 0; end
       4'b0101 : begin vout[0]= 0; vout[1]= 1; vout[2]= 0; vout[3]= 0; end
       4'b0110 : begin vout[0]= 0; vout[1]= 0; vout[2]= 1; vout[3]= 0; end
       4'b0111 : begin vout[0]= 0; vout[1]= 0; vout[2]= 0; vout[3]= 1; end
       4'b1000 : begin vout[0]=-1; vout[1]= 0; vout[2]= 0; vout[3]= 0; end
       4'b1001 : begin vout[0]= 0; vout[1]=-1; vout[2]= 0; vout[3]= 0; end
       4'b1010 : begin vout[0]= 0; vout[1]= 0; vout[2]=-1; vout[3]= 0; end
       4'b1011 : begin vout[0]= 0; vout[1]= 0; vout[2]= 0; vout[3]=-1; end
       4'b1100 : begin vout[0]=-3; vout[1]= 0; vout[2]= 0; vout[3]= 0; end
       4'b1101 : begin vout[0]= 0; vout[1]=-3; vout[2]= 0; vout[3]= 0; end
       4'b1110 : begin vout[0]= 0; vout[1]= 0; vout[2]=-3; vout[3]= 0; end
       4'b1111 : begin vout[0]= 0; vout[1]= 0; vout[2]= 0; vout[3]=-3; end
    endcase

    V(out) <+ transition(vout,td, tt);

  end //analog
endmodule

Hi Yongjin,

It looks as though your intent is to set individual bits within "result" to indicate whether V(in[i]) is above or below a certain threshold. However, declaring "result" as

integer result [0:3];

will give you an array of four integers, and not four bits. The compiler reports an error on the "case(result)" line because it expects to receive an integer value, rather than an array of integers (it could concatenate the integers together into a big bitfield, but I don't think that would give you the result that you expect based on your case-stmnt contents).

The way to address this issue is to simply use

integer result;

as your datatype, since a single integer contains more than four bits. You can then use bitwise ops, along with shifts, to set the proper bits as follows:

analog begin
    result = 0;
    for (i=0; i < 4; i=i+1) begin
      if(V(in[i]) >= thresh)
              result = result | (1 << i);
    end //for

.... case stmnt goes here unchanged, etc.

Lastly, on your transition statement, you would want to loop through each of the values as follows:

for(i = 0; i < 4; i = i+1)
       V(out[i]) <+ transition(vout[i],td, tt);

As Geoffrey mentions above, your bit order (most significant bit vs. least significant bit) may or (may not) be in the order that you intended, so that might be something to have a look at as well.

- Boris