arraycast_demo.va

// arraycast_demo.va -- Enhancement-214: whole-array type coercion.
//
// Both array spellings in this model used to CRASH the compiler, because an
// integer array element reached a float MIR op that the constant evaluator has
// no case for ("invalid operation fdiv Int(1) Float(..)"):
//
//   * `num` is an INTEGER array variable used as a laplace_nd coefficient
//     vector. Coefficient vectors are real per LRM 9.19, but the elements of an
//     integer array read back as i32 and hit the fmul/fsub/fdiv of the internal
//     state-space realization.
//
//   * the `case` discriminant `sel` is a REAL array while the items are written
//     `{1}` / `{2}`. The comparison opcode is chosen from the discriminant --
//     Feq, for a real array -- but the items' integer elements lower to i32.
//
// Neither spelling is exotic: `{1}` is simply how a unity coefficient and a
// small integer selector are naturally written. Both now coerce to real, and
// -- verified in verify_arraycast.py -- the compiled result is bit-identical to
// the same model written '{1.0} / '{2.0} throughout, so nothing is silently
// mis-lowered in the process.
//
// The model itself is a unity-numerator first-order low-pass with a
// mode-selected gain:  H(s) = gain / (1 + tau*s).

`include "disciplines.vams"

module arraycast_demo(in, out);
    input in;
    output out;
    electrical in, out;

    parameter real tau  = 1e-6 from (0:inf);
    parameter real mode = 1    from [1:3];

    integer num[0:0];    // integer array VARIABLE as a real coefficient vector
    real    sel[0:0];    // real discriminant vs integer case items
    real    gain;

    analog begin
        num[0] = 1;                       // unity numerator, written as an integer
        sel[0] = mode;

        case (sel)
            {1}:     gain = 1.0;
            {2}:     gain = 2.0;
            default: gain = 0.5;          // mode 3
        endcase

        V(out) <+ gain * laplace_nd(V(in), num, '{1.0, tau});
    end
endmodule