Altera_Forum
Honored Contributor
Honored Contributorsigned/unsigned multipliers
I can't seem to find a way to instantiate a multiplier that will dynamically select between signed and unsigned multiplication. This is on a Cyclone II, but applies to other parts as well.
Reading the Cyclone II documentation it is clear that signa, signb inputs does what I want, but none of the multipliers created with the Wizzard exports that as an input signal. Trying to infer it with the code below doesn't work (bug in Quartus II?); it complains that no logic depends on input_sign. However looking at the RTL with Tools/Netlist Viewers/RTL Viewer clearly shows it being used, however the technology map viewer shows input_sign as disconnected and signa and signb hardwired to ground. This looks like a bug to me, but I could be doing something wrong.
module mult(input clock,
input input_sign,
input input_a,
input input_b,
output reg output_c);
reg a, b;
reg sign;
always @(posedge clock) begin
sign <= input_sign;
a <= input_a;
b <= input_b;
if (sign)
output_c <= $signed(a) * $signed(b);
else
output_c <= $unsigned(a) * $unsigned(b);
end
endmodule
