Add a simple direct mapped icache

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>

Makefile

@@ -12,8 +12,8 @@ all: $(all)
 	$(GHDL) -a $(GHDLFLAGS) $<
 
 common.o: decode_types.o
-core_tb.o: common.o wishbone_types.o soc.o
-core.o: common.o wishbone_types.o fetch1.o fetch2.o decode1.o decode2.o register_file.o cr_file.o execute1.o execute2.o loadstore1.o loadstore2.o multiply.o writeback.o
+core_tb.o: common.o core.o soc.o
+core.o: common.o wishbone_types.o fetch1.o fetch2.o icache.o decode1.o decode2.o register_file.o cr_file.o execute1.o execute2.o loadstore1.o loadstore2.o multiply.o writeback.o
 cr_file.o: common.o
 crhelpers.o: common.o
 decode1.o: common.o decode_types.o
@@ -26,6 +26,7 @@ fetch2.o: common.o wishbone_types.o
 glibc_random_helpers.o:
 glibc_random.o: glibc_random_helpers.o
 helpers.o:
+icache.o: common.o wishbone_types.o
 insn_helpers.o:
 loadstore1.o: common.o
 loadstore2.o: common.o helpers.o wishbone_types.o

common.vhdl

@@ -31,6 +31,16 @@ package common is
 	end record;
 	constant Decode1ToDecode2Init : Decode1ToDecode2Type := (valid => '0', decode => decode_rom_init, others => (others => '0'));
 
+	type Fetch2ToIcacheType is record
+		req: std_ulogic;
+		addr: std_ulogic_vector(63 downto 0);
+	end record;
+
+	type IcacheToFetch2Type is record
+		ack: std_ulogic;
+		insn: std_ulogic_vector(31 downto 0);
+	end record;
+
 	type Decode2ToExecute1Type is record
 		valid: std_ulogic;
 		insn_type: insn_type_t;

core.vhdl

@@ -31,6 +31,10 @@ architecture behave of core is
     signal fetch1_to_fetch2: Fetch1ToFetch2Type;
     signal fetch2_to_decode1: Fetch2ToDecode1Type;
 
+    -- icache signals
+    signal fetch2_to_icache : Fetch2ToIcacheType;
+    signal icache_to_fetch2 : IcacheToFetch2Type;
+
     -- decode signals
     signal decode1_to_decode2: Decode1ToDecode2Type;
     signal decode2_to_execute1: Decode2ToExecute1Type;
@@ -97,14 +101,28 @@ begin
             stall_in => fetch2_stall_in,
             stall_out => fetch2_stall_out,
             flush_in => flush,
-            wishbone_in => wishbone_insn_in,
-            wishbone_out => wishbone_insn_out,
+            i_in => icache_to_fetch2,
+            i_out => fetch2_to_icache,
             f_in => fetch1_to_fetch2,
             f_out => fetch2_to_decode1
             );
 
     fetch2_stall_in <= decode2_stall_out;
 
+    icache_0: entity work.icache
+        generic map(
+            LINE_SIZE_DW => 8,
+            NUM_LINES => 16
+            )
+        port map(
+            clk => clk,
+            rst => rst,
+            i_in => fetch2_to_icache,
+            i_out => icache_to_fetch2,
+            wishbone_out => wishbone_insn_out,
+            wishbone_in => wishbone_insn_in
+            );
+
     decode1_0: entity work.decode1
         port map (
             clk => clk,

core_tb.vhdl

@@ -1,7 +1,5 @@
 library ieee;
 use ieee.std_logic_1164.all;
-use ieee.numeric_std.all;
-use std.textio.all;
 
 library work;
 use work.common.all;

fetch2.vhdl

@@ -16,9 +16,8 @@ entity fetch2 is
 
 		flush_in     : in std_ulogic;
 
-		-- instruction memory interface
-		wishbone_in  : in wishbone_slave_out;
-		wishbone_out : out wishbone_master_out;
+		i_in         : in IcacheToFetch2Type;
+		i_out        : out Fetch2ToIcacheType;
 
 		f_in         : in Fetch1ToFetch2Type;
 
@@ -27,35 +26,7 @@ entity fetch2 is
 end entity fetch2;
 
 architecture behaviour of fetch2 is
-	type state_type is (IDLE, JUST_IDLE, WAIT_ACK, WAIT_ACK_THROWAWAY);
-
-	type reg_internal_type is record
-		state     : state_type;
-		nia       : std_ulogic_vector(63 downto 0);
-		w         : wishbone_master_out;
-		-- Trivial 64B cache
-		cache     : std_ulogic_vector(63 downto 0);
-		tag       : std_ulogic_vector(60 downto 0);
-		tag_valid : std_ulogic;
-	end record;
-
-	function wishbone_fetch(nia : std_ulogic_vector(63 downto 0)) return wishbone_master_out is
-		variable w : wishbone_master_out;
-	begin
-		assert nia(2 downto 0) = "000";
-
-		w.adr := nia;
-		w.dat := (others => '0');
-		w.cyc := '1';
-		w.stb := '1';
-		w.sel := "11111111";
-		w.we  := '0';
-
-		return w;
-	end;
-
 	signal r, rin : Fetch2ToDecode1Type;
-	signal r_int, rin_int : reg_internal_type;
 begin
 	regs : process(clk)
 	begin
@@ -64,96 +35,31 @@ begin
 			if rst = '1' or flush_in = '1' or stall_in = '0' then
 				r <= rin;
 			end if;
-			r_int <= rin_int;
 		end if;
 	end process;
 
 	comb : process(all)
 		variable v : Fetch2ToDecode1Type;
-		variable v_int : reg_internal_type;
 	begin
 		v := r;
-		v_int := r_int;
 
-		v.valid := '0';
+		-- 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;
 
-		case v_int.state is
-		when IDLE | JUST_IDLE =>
-			v_int.state := IDLE;
-
-			if (v_int.tag_valid = '1') and (v_int.tag = f_in.nia(63 downto 3)) then
-				v.valid := '1';
-				if f_in.nia(2) = '0' then
-					v.insn := v_int.cache(31 downto 0);
-				else
-					v.insn := v_int.cache(63 downto 32);
-				end if;
-			else
-				v_int.state := WAIT_ACK;
-				v_int.nia := f_in.nia;
-				v_int.w := wishbone_fetch(f_in.nia(63 downto 3) & "000");
-			end if;
-
-		when WAIT_ACK =>
-			if wishbone_in.ack = '1' then
-				v_int.state := IDLE;
-				v_int.w := wishbone_master_out_init;
-				v_int.cache := wishbone_in.dat;
-				v_int.tag := v_int.nia(63 downto 3);
-				v_int.tag_valid := '1';
-
-				v.valid := '1';
-				if v_int.nia(2) = '0' then
-					v.insn := v_int.cache(31 downto 0);
-				else
-					v.insn := v_int.cache(63 downto 32);
-				end if;
-			end if;
-
-		when WAIT_ACK_THROWAWAY =>
-			if wishbone_in.ack = '1' then
-				-- Should we put the returned data in the cache? We went to the
-				-- trouble of fetching it and it might be useful in the future
-
-				v_int.w := wishbone_master_out_init;
-
-				-- We need to stall fetch1 for one more cycle, so transition through JUST_IDLE
-				v_int.state := JUST_IDLE;
-			end if;
-		end case;
-
-		stall_out <= '0';
-		if v_int.state /= IDLE then
-			stall_out <= '1';
-		end if;
 
 		if flush_in = '1' then
 			v.valid := '0';
-
-			-- Throw away in flight data
-			if v_int.state = WAIT_ACK then
-				v_int.state := WAIT_ACK_THROWAWAY;
-			end if;
-		end if;
-
-		if rst = '1' then
-			v := Fetch2ToDecode1Init;
-
-			v_int.state := IDLE;
-			v_int.nia := (others => '0');
-			v_int.w := wishbone_master_out_init;
-			v_int.cache := (others => '0');
-			v_int.tag := (others => '0');
-			v_int.tag_valid := '0';
 		end if;
 
 		-- Update registers
-		rin_int <= v_int;
 		rin <= v;
 
 		-- Update outputs
 		f_out <= r;
-		wishbone_out <= r_int.w;
 	end process;
 end architecture behaviour;

icache.vhdl

@@ -0,0 +1,173 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+library work;
+use work.common.all;
+use work.wishbone_types.all;
+
+-- 64 bit direct mapped icache. All instructions are 4B aligned.
+
+entity icache is
+    generic (
+        -- Line size in 64bit doublewords
+        LINE_SIZE_DW : natural := 8;
+        -- Number of lines
+        NUM_LINES : natural := 32
+        );
+    port (
+        clk          : in std_ulogic;
+        rst          : in std_ulogic;
+
+        i_in         : in Fetch2ToIcacheType;
+        i_out        : out IcacheToFetch2Type;
+
+        wishbone_out : out wishbone_master_out;
+        wishbone_in  : in wishbone_slave_out
+        );
+end entity icache;
+
+architecture rtl of icache is
+    function log2(i : natural) return integer is
+        variable tmp : integer := i;
+        variable ret : integer := 0;
+    begin
+        while tmp > 1 loop
+            ret  := ret + 1;
+            tmp := tmp / 2;
+        end loop;
+        return ret;
+    end function;
+
+    function ispow2(i : integer) return boolean is
+    begin
+        if to_integer(to_unsigned(i, 32) and to_unsigned(i - 1, 32)) = 0 then
+            return true;
+        else
+            return false;
+        end if;
+    end function;
+
+    constant LINE_SIZE : natural := LINE_SIZE_DW*8;
+    constant OFFSET_BITS : natural := log2(LINE_SIZE);
+    constant INDEX_BITS : natural := log2(NUM_LINES);
+    constant TAG_BITS : natural := 64 - OFFSET_BITS - INDEX_BITS;
+
+    subtype cacheline_type is std_logic_vector((LINE_SIZE*8)-1 downto 0);
+    type cacheline_array is array(0 to NUM_LINES-1) of cacheline_type;
+
+    subtype cacheline_tag_type is std_logic_vector(TAG_BITS-1 downto 0);
+    type cacheline_tag_array is array(0 to NUM_LINES-1) of cacheline_tag_type;
+
+    signal cachelines : cacheline_array := (others => (others => '0'));
+    signal tags       : cacheline_tag_array := (others => (others => '0'));
+    signal tags_valid : std_ulogic_vector(NUM_LINES-1 downto 0) := (others => '0');
+
+    attribute ram_style : string;
+    attribute ram_style of cachelines : signal is "block";
+
+    attribute ram_decomp : string;
+    attribute ram_decomp of cachelines : signal is "power";
+
+    type state_type is (IDLE, WAIT_ACK);
+
+    type reg_internal_type is record
+        state : state_type;
+        w     : wishbone_master_out;
+        store_index     : integer range 0 to (NUM_LINES-1);
+        store_word  : integer range 0 to (LINE_SIZE-1);
+    end record;
+
+    signal r : reg_internal_type;
+
+    signal read_index : integer range 0 to NUM_LINES-1;
+    signal read_tag   : std_ulogic_vector(63-OFFSET_BITS-INDEX_BITS downto 0);
+    signal read_miss  : boolean;
+
+    function get_index(addr: std_ulogic_vector(63 downto 0)) return integer is
+    begin
+        return to_integer(unsigned(addr((OFFSET_BITS+INDEX_BITS-1) downto OFFSET_BITS)));
+    end;
+
+    function get_word(addr: std_ulogic_vector(63 downto 0); data: cacheline_type) return std_ulogic_vector is
+        variable word : integer;
+    begin
+        word := to_integer(unsigned(addr(OFFSET_BITS-1 downto 2)));
+        return data((word+1)*32-1 downto word*32);
+    end;
+
+    function get_tag(addr: std_ulogic_vector(63 downto 0)) return std_ulogic_vector is
+    begin
+        return addr(63 downto OFFSET_BITS+INDEX_BITS);
+    end;
+begin
+    assert ispow2(LINE_SIZE) report "LINE_SIZE not power of 2" severity FAILURE;
+    assert ispow2(NUM_LINES) report "NUM_LINES not power of 2" severity FAILURE;
+
+    icache_read : process(all)
+    begin
+        read_index <= get_index(i_in.addr);
+        read_tag <= get_tag(i_in.addr);
+        read_miss <= false;
+
+        i_out.ack <= '0';
+        i_out.insn <= get_word(i_in.addr, cachelines(read_index));
+
+        if i_in.req = '1' then
+            if (tags_valid(read_index) = '1') and (tags(read_index) = read_tag) then
+                -- report hit asynchronously
+                i_out.ack <= '1';
+            else
+                read_miss <= true;
+            end if;
+        end if;
+    end process;
+
+    wishbone_out <= r.w;
+
+    icache_write : process(clk)
+    begin
+        if rising_edge(clk) then
+            if rst = '1' then
+                tags_valid <= (others => '0');
+                r.state <= IDLE;
+                r.w.cyc <= '0';
+                r.w.stb <= '0';
+            end if;
+
+            r.w.dat <= (others => '0');
+            r.w.sel <= "11111111";
+            r.w.we  <= '0';
+
+            case r.state is
+                when IDLE =>
+                    if read_miss = true then
+                        r.state <= WAIT_ACK;
+                        r.store_word <= 0;
+                        r.store_index <= read_index;
+
+                        tags(read_index) <= read_tag;
+                        tags_valid(read_index) <= '0';
+
+                        r.w.adr <= i_in.addr(63 downto OFFSET_BITS) & (OFFSET_BITS-1 downto 0 => '0');
+                        r.w.cyc <= '1';
+                        r.w.stb <= '1';
+                    end if;
+                when WAIT_ACK =>
+                    if wishbone_in.ack = '1' then
+                        cachelines(r.store_index)((r.store_word+1)*64-1 downto ((r.store_word)*64)) <= wishbone_in.dat;
+                        r.store_word <= r.store_word + 1;
+
+                        if r.store_word = (LINE_SIZE_DW-1) then
+                            r.state <= IDLE;
+                            tags_valid(r.store_index) <= '1';
+                            r.w.cyc <= '0';
+                            r.w.stb <= '0';
+                        else
+                            r.w.adr(OFFSET_BITS-1 downto 3) <= std_ulogic_vector(to_unsigned(r.store_word+1, OFFSET_BITS-3));
+                        end if;
+                    end if;
+            end case;
+        end if;
+    end process;
+end;

microwatt.core

@@ -26,6 +26,7 @@ filesets:
       - writeback.vhdl
       - insn_helpers.vhdl
       - core.vhdl
+      - icache.vhdl
     file_type : vhdlSource-2008
 
   soc: