Support for 'keep' boolean attribute

[anfractuosity]

Hi,

I'm just wondering if it would be possible to pass the keep attribute to yosys so that the following kind of use of it would work:

architecture blink of leds is

signal clk_4hz: std_logic := '0';
constant gates: integer := 3 - 1;
signal max: integer := 3e6;
signal A: std_logic_vector(0 to gates) := ( others => '0');

attribute keep: boolean;
attribute keep of A: signal is true;  

signal B: std_logic := '1';
signal C: std_logic := '1';
signal val: std_logic := '0';
signal data: std_logic := '0';

begin 
  process (clk)
    variable counter : unsigned (23 downto 0) := (others => '0');
  begin
    if rising_edge(clk) then
      if counter >= max then
        counter := x"000000";
        clk_4hz <= not clk_4hz;
      else
        counter := counter + 1;
      end if;
    end if;
  end process;

GEN:
    for i in 0 to gates generate
        A(i) <= not A(gates - i);    
    end generate GEN;

  led2 <= clk_4hz;
  led3 <= clk_4hz;
  led4 <= clk_4hz;
  led5 <= clk_4hz;
end;

Many thanks!

[tgingold]

So keep is currently handled in the front-end, but not always propagated to yosys. Still WIP.