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Altera_Forum's avatar
Altera_Forum
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10 years ago

Problem with while loop in an array

I need to check how many cells in an array are "filled" and how many are zeroed. The array is a one-dimensional array of 64 bits vector. Declaration in package: package my_pack is typ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

A for loop will work in your case, as you're only going through every entry in the table. With the while loop, imagine what would happen if no entries are 0? it will just loop forever, in 0 time. The synthesisor has no way of knowing that some entries will always be zero.

You just need a for loop that updates a counter. 


process(clk)
  variable num_packets : integer;
begin
  if rising_edge(clk) begin
    num_packets := 0;
    for i in packets_in'range loop
      if packets_in(i) /= ZERO_64 then
        num_packets := num_packets + 1;
      end if;
    end loop;
    output <= num_packets;
  end if;
end process;

Here, the compiler knows exacly how many loop iterations there are, and can generate the adder circuit required.