read_rtlil <<EOT
module \top
  wire input 3 \A
  wire width 2 input 2 \B
  wire width 2 input 1 \S
  wire \Y
  cell $pmux \my_pmux
    parameter signed \S_WIDTH 2
    parameter signed \WIDTH 1
    connect \A \A
    connect \B \B
    connect \S \S
    connect \Y \Y
  end
end
EOT

assertpmux