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array_examples — Verilog-A array literals / aggregates (Enhancement-14)

Demonstrates the three array-aggregate capabilities added in Enhancement-14, using version11's own openvaf-r and ngspice-46:

# Capability Syntax
A Whole-array aggregate assignment and copy acc = '{a, b, c}; · b = a;
B Array-valued parameters (per-element default and override) parameter real [0:3] w = '{...};
C Dynamic (non-constant) indexing rev[i] = acc[3 - i]; in a for loop

Both models are programmable-gain buffers: V(out) = gain * V(in), where the gain is computed through the array machinery, so measuring V(out) at V(in)=1 reads the gain back directly.

Files

File Purpose
array_demo.va 4-tap gain buffer exercising A + B + C together. Gain = w[0]+w[1]+w[2]+w[3].
array_copy.va Whole-array copy b = a and integer→real element promotion (a = '{1,2,3}).
verify_array.py Compiles both, drives them through ngspice, asserts gains against closed forms.

Run

python3 verify_array.py

Expected:

array_demo default (w='{0.1,0.2,0.3,0.4})         1.000000     1.000000  PASS
array_demo override w[0..3]=0.3,0.4,0.5,0.6       1.800000     1.800000  PASS
array_demo override w[2]=0.9 only                 1.600000     1.600000  PASS
array_copy (b=a='{1,2,3}) gain                    0.600000     0.600000  PASS
ALL PASS

Notes

  • Array declaration syntax is range-before-name: real [0:3] w; (as for vectored nets and Enhancement-4 array variables), not real w[0:3];.
  • Array parameters expand into one scalar OSDI parameter per element, named w[0], w[1], … — ngspice overrides each individually in a .model card (.model mm array_demo(w[2]=0.9)); unset elements keep their literal default. Element order follows the declared range ([msb:lsb]), so [2:0] fills the literal from w[2] down to w[0].
  • Dynamic indexing applies to array variables (mutable state). Array parameters are constant tables and are read by a constant index; to index a parameter table dynamically, copy it into an array variable first (as array_demo does: acc = '{w[0], w[1], w[2], w[3]}, then acc[i]).
  • A dynamic index lowers to a runtime select over the element variables, so its cost grows with the array length — fine for the small coefficient arrays these features target.