antonblanchard.microwatt/fetch2.vhdl

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.common.all;
use work.wishbone_types.all;

entity fetch2 is
	port(
		clk          : in std_ulogic;
		rst          : in std_ulogic;

		stall_in     : in std_ulogic;
		stall_out    : out std_ulogic;

		flush_in     : in std_ulogic;

		i_in         : in IcacheToFetch2Type;
		i_out        : out Fetch2ToIcacheType;

		f_in         : in Fetch1ToFetch2Type;

		f_out        : out Fetch2ToDecode1Type
	);
end entity fetch2;

architecture behaviour of fetch2 is
	signal r, rin : Fetch2ToDecode1Type;
begin
	regs : process(clk)
	begin
		if rising_edge(clk) then
			-- Output state remains unchanged on stall, unless we are flushing
			if rst = '1' or flush_in = '1' or stall_in = '0' then
				r <= rin;
			end if;
		end if;
	end process;

	comb : process(all)
		variable v : Fetch2ToDecode1Type;
	begin
		v := r;

		-- asynchronous icache lookup
		i_out.req <= '1';
		i_out.addr <= f_in.nia;
		v.valid := i_in.ack;
		v.nia := f_in.nia;
		v.insn := i_in.insn;
		stall_out <= not i_in.ack;


		if flush_in = '1' then
			v.valid := '0';
		end if;

		-- Update registers
		rin <= v;

		-- Update outputs
		f_out <= r;
	end process;
end architecture behaviour;