dcache: Add a dcache
This replaces loadstore2 with a dcache The dcache unit is losely based on the icache one (same basic cache layout), but has some significant logic additions to deal with stores, loads with update, non-cachable accesses and other differences due to operating in the execution part of the pipeline rather than the fetch part. The cache is store-through, though a hit with an existing line will update the line rather than invalidate it. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>pull/114/head
Benjamin Herrenschmidt
6 years ago
parent
7b3df7cb05
commit
b513f0fb48
@ -0,0 +1,733 @@
|
||||
--
|
||||
-- Set associative dcache write-through
|
||||
--
|
||||
-- TODO (in no specific order):
|
||||
--
|
||||
-- * See list in icache.vhdl
|
||||
-- * Complete load misses on the cycle when WB data comes instead of
|
||||
-- at the end of line (this requires dealing with requests coming in
|
||||
-- while not idle...)
|
||||
--
|
||||
library ieee;
|
||||
use ieee.std_logic_1164.all;
|
||||
use ieee.numeric_std.all;
|
||||
|
||||
library work;
|
||||
use work.common.all;
|
||||
use work.helpers.all;
|
||||
use work.wishbone_types.all;
|
||||
|
||||
entity dcache is
|
||||
generic (
|
||||
-- Line size in bytes
|
||||
LINE_SIZE : positive := 64;
|
||||
-- Number of lines in a set
|
||||
NUM_LINES : positive := 32;
|
||||
-- Number of ways
|
||||
NUM_WAYS : positive := 4
|
||||
);
|
||||
port (
|
||||
clk : in std_ulogic;
|
||||
rst : in std_ulogic;
|
||||
|
||||
d_in : in Loadstore1ToDcacheType;
|
||||
d_out : out DcacheToWritebackType;
|
||||
|
||||
wishbone_out : out wishbone_master_out;
|
||||
wishbone_in : in wishbone_slave_out
|
||||
);
|
||||
end entity dcache;
|
||||
|
||||
architecture rtl of dcache 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;
|
||||
|
||||
-- BRAM organisation: We never access more than wishbone_data_bits at
|
||||
-- a time so to save resources we make the array only that wide, and
|
||||
-- use consecutive indices for to make a cache "line"
|
||||
--
|
||||
-- ROW_SIZE is the width in bytes of the BRAM (based on WB, so 64-bits)
|
||||
constant ROW_SIZE : natural := wishbone_data_bits / 8;
|
||||
-- ROW_PER_LINE is the number of row (wishbone transactions) in a line
|
||||
constant ROW_PER_LINE : natural := LINE_SIZE / ROW_SIZE;
|
||||
-- BRAM_ROWS is the number of rows in BRAM needed to represent the full
|
||||
-- dcache
|
||||
constant BRAM_ROWS : natural := NUM_LINES * ROW_PER_LINE;
|
||||
|
||||
-- Bit fields counts in the address
|
||||
|
||||
-- ROW_BITS is the number of bits to select a row
|
||||
constant ROW_BITS : natural := log2(BRAM_ROWS);
|
||||
-- ROW_LINEBITS is the number of bits to select a row within a line
|
||||
constant ROW_LINEBITS : natural := log2(ROW_PER_LINE);
|
||||
-- LINE_OFF_BITS is the number of bits for the offset in a cache line
|
||||
constant LINE_OFF_BITS : natural := log2(LINE_SIZE);
|
||||
-- ROW_OFF_BITS is the number of bits for the offset in a row
|
||||
constant ROW_OFF_BITS : natural := log2(ROW_SIZE);
|
||||
-- INDEX_BITS is the number if bits to select a cache line
|
||||
constant INDEX_BITS : natural := log2(NUM_LINES);
|
||||
-- TAG_BITS is the number of bits of the tag part of the address
|
||||
constant TAG_BITS : natural := 64 - LINE_OFF_BITS - INDEX_BITS;
|
||||
-- WAY_BITS is the number of bits to select a way
|
||||
constant WAY_BITS : natural := log2(NUM_WAYS);
|
||||
|
||||
-- Example of layout for 32 lines of 64 bytes:
|
||||
--
|
||||
-- .. tag |index| line |
|
||||
-- .. | row | |
|
||||
-- .. | |---| | ROW_LINEBITS (3)
|
||||
-- .. | |--- - --| LINE_OFF_BITS (6)
|
||||
-- .. | |- --| ROW_OFF_BITS (3)
|
||||
-- .. |----- ---| | ROW_BITS (8)
|
||||
-- .. |-----| | INDEX_BITS (5)
|
||||
-- .. --------| | TAG_BITS (53)
|
||||
|
||||
subtype row_t is integer range 0 to BRAM_ROWS-1;
|
||||
subtype index_t is integer range 0 to NUM_LINES-1;
|
||||
subtype way_t is integer range 0 to NUM_WAYS-1;
|
||||
|
||||
-- The cache data BRAM organized as described above for each way
|
||||
subtype cache_row_t is std_ulogic_vector(wishbone_data_bits-1 downto 0);
|
||||
|
||||
-- The cache tags LUTRAM has a row per set. Vivado is a pain and will
|
||||
-- not handle a clean (commented) definition of the cache tags as a 3d
|
||||
-- memory. For now, work around it by putting all the tags
|
||||
subtype cache_tag_t is std_logic_vector(TAG_BITS-1 downto 0);
|
||||
-- type cache_tags_set_t is array(way_t) of cache_tag_t;
|
||||
-- type cache_tags_array_t is array(index_t) of cache_tags_set_t;
|
||||
constant TAG_RAM_WIDTH : natural := TAG_BITS * NUM_WAYS;
|
||||
subtype cache_tags_set_t is std_logic_vector(TAG_RAM_WIDTH-1 downto 0);
|
||||
type cache_tags_array_t is array(index_t) of cache_tags_set_t;
|
||||
|
||||
-- The cache valid bits
|
||||
subtype cache_way_valids_t is std_ulogic_vector(NUM_WAYS-1 downto 0);
|
||||
type cache_valids_t is array(index_t) of cache_way_valids_t;
|
||||
|
||||
-- Storage. Hopefully "cache_rows" is a BRAM, the rest is LUTs
|
||||
signal cache_tags : cache_tags_array_t;
|
||||
signal cache_valids : cache_valids_t;
|
||||
|
||||
attribute ram_style : string;
|
||||
attribute ram_style of cache_tags : signal is "distributed";
|
||||
|
||||
-- Type of operation on a "valid" input
|
||||
type op_t is (OP_NONE,
|
||||
OP_LOAD_HIT, -- Cache hit on load
|
||||
OP_LOAD_MISS, -- Load missing cache
|
||||
OP_LOAD_NC, -- Non-cachable load
|
||||
OP_BAD, -- BAD: Cache hit on NC load/store
|
||||
OP_STORE_HIT, -- Store hitting cache
|
||||
OP_STORE_MISS); -- Store missing cache
|
||||
|
||||
-- Cache state machine
|
||||
type state_t is (IDLE, -- Normal load hit processing
|
||||
LOAD_UPDATE, -- Load with update address update cycle
|
||||
RELOAD_WAIT_ACK, -- Cache reload wait ack
|
||||
STORE_WAIT_ACK, -- Store wait ack
|
||||
NC_LOAD_WAIT_ACK);-- Non-cachable load wait ack
|
||||
|
||||
type reg_internal_t is record
|
||||
req_latch : Loadstore1ToDcacheType;
|
||||
|
||||
-- Cache hit state (Latches for 1 cycle BRAM access)
|
||||
hit_way : way_t;
|
||||
hit_load_valid : std_ulogic;
|
||||
|
||||
-- Register update (load/store with update)
|
||||
update_valid : std_ulogic;
|
||||
|
||||
-- Data buffer for "slow" read ops (load miss and NC loads).
|
||||
slow_data : std_ulogic_vector(63 downto 0);
|
||||
slow_valid : std_ulogic;
|
||||
|
||||
-- Cache miss state (reload state machine)
|
||||
state : state_t;
|
||||
wb : wishbone_master_out;
|
||||
store_way : way_t;
|
||||
store_index : index_t;
|
||||
end record;
|
||||
|
||||
signal r : reg_internal_t;
|
||||
|
||||
-- Async signals on incoming request
|
||||
signal req_index : index_t;
|
||||
signal req_row : row_t;
|
||||
signal req_hit_way : way_t;
|
||||
signal req_tag : cache_tag_t;
|
||||
signal req_op : op_t;
|
||||
|
||||
-- Cache RAM interface
|
||||
type cache_ram_out_t is array(way_t) of cache_row_t;
|
||||
signal cache_out : cache_ram_out_t;
|
||||
|
||||
-- PLRU output interface
|
||||
type plru_out_t is array(index_t) of std_ulogic_vector(WAY_BITS-1 downto 0);
|
||||
signal plru_victim : plru_out_t;
|
||||
|
||||
-- Wishbone read/write/cache write formatting signals
|
||||
signal bus_sel : wishbone_sel_type;
|
||||
signal store_data : wishbone_data_type;
|
||||
|
||||
-- Return the cache line index (tag index) for an address
|
||||
function get_index(addr: std_ulogic_vector(63 downto 0)) return index_t is
|
||||
begin
|
||||
return to_integer(unsigned(addr(63-TAG_BITS downto LINE_OFF_BITS)));
|
||||
end;
|
||||
|
||||
-- Return the cache row index (data memory) for an address
|
||||
function get_row(addr: std_ulogic_vector(63 downto 0)) return row_t is
|
||||
begin
|
||||
return to_integer(unsigned(addr(63-TAG_BITS downto ROW_OFF_BITS)));
|
||||
end;
|
||||
|
||||
-- Returns whether this is the last row of a line
|
||||
function is_last_row(addr: std_ulogic_vector(63 downto 0)) return boolean is
|
||||
constant ones : std_ulogic_vector(ROW_LINEBITS-1 downto 0) := (others => '1');
|
||||
begin
|
||||
return addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) = ones;
|
||||
end;
|
||||
|
||||
-- Return the address of the next row in the current cache line
|
||||
function next_row_addr(addr: std_ulogic_vector(63 downto 0)) return std_ulogic_vector is
|
||||
variable row_idx : std_ulogic_vector(ROW_LINEBITS-1 downto 0);
|
||||
variable result : std_ulogic_vector(63 downto 0);
|
||||
begin
|
||||
-- Is there no simpler way in VHDL to generate that 3 bits adder ?
|
||||
row_idx := addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS);
|
||||
row_idx := std_ulogic_vector(unsigned(row_idx) + 1);
|
||||
result := addr;
|
||||
result(LINE_OFF_BITS-1 downto ROW_OFF_BITS) := row_idx;
|
||||
return result;
|
||||
end;
|
||||
|
||||
-- Get the tag value from the address
|
||||
function get_tag(addr: std_ulogic_vector(63 downto 0)) return cache_tag_t is
|
||||
begin
|
||||
return addr(63 downto 64-TAG_BITS);
|
||||
end;
|
||||
|
||||
-- Read a tag from a tag memory row
|
||||
function read_tag(way: way_t; tagset: cache_tags_set_t) return cache_tag_t is
|
||||
begin
|
||||
return tagset((way+1) * TAG_BITS - 1 downto way * TAG_BITS);
|
||||
end;
|
||||
|
||||
-- Write a tag to tag memory row
|
||||
procedure write_tag(way: in way_t; tagset: inout cache_tags_set_t;
|
||||
tag: cache_tag_t) is
|
||||
begin
|
||||
tagset((way+1) * TAG_BITS - 1 downto way * TAG_BITS) := tag;
|
||||
end;
|
||||
|
||||
-- Generate byte enables from sizes
|
||||
function length_to_sel(length : in std_logic_vector(3 downto 0)) return std_ulogic_vector is
|
||||
begin
|
||||
case length is
|
||||
when "0001" =>
|
||||
return "00000001";
|
||||
when "0010" =>
|
||||
return "00000011";
|
||||
when "0100" =>
|
||||
return "00001111";
|
||||
when "1000" =>
|
||||
return "11111111";
|
||||
when others =>
|
||||
return "00000000";
|
||||
end case;
|
||||
end function length_to_sel;
|
||||
|
||||
-- Calculate shift and byte enables for wishbone
|
||||
function wishbone_data_shift(address : in std_ulogic_vector(63 downto 0)) return natural is
|
||||
begin
|
||||
return to_integer(unsigned(address(2 downto 0))) * 8;
|
||||
end function wishbone_data_shift;
|
||||
|
||||
function wishbone_data_sel(size : in std_logic_vector(3 downto 0);
|
||||
address : in std_logic_vector(63 downto 0))
|
||||
return std_ulogic_vector is
|
||||
begin
|
||||
return std_ulogic_vector(shift_left(unsigned(length_to_sel(size)),
|
||||
to_integer(unsigned(address(2 downto 0)))));
|
||||
end function wishbone_data_sel;
|
||||
|
||||
begin
|
||||
|
||||
assert LINE_SIZE mod ROW_SIZE = 0 report "LINE_SIZE not multiple of ROW_SIZE" severity FAILURE;
|
||||
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;
|
||||
assert ispow2(ROW_PER_LINE) report "ROW_PER_LINE not power of 2" severity FAILURE;
|
||||
assert (ROW_BITS = INDEX_BITS + ROW_LINEBITS)
|
||||
report "geometry bits don't add up" severity FAILURE;
|
||||
assert (LINE_OFF_BITS = ROW_OFF_BITS + ROW_LINEBITS)
|
||||
report "geometry bits don't add up" severity FAILURE;
|
||||
assert (64 = TAG_BITS + INDEX_BITS + LINE_OFF_BITS)
|
||||
report "geometry bits don't add up" severity FAILURE;
|
||||
assert (64 = TAG_BITS + ROW_BITS + ROW_OFF_BITS)
|
||||
report "geometry bits don't add up" severity FAILURE;
|
||||
assert (64 = wishbone_data_bits)
|
||||
report "Can't yet handle a wishbone width that isn't 64-bits" severity FAILURE;
|
||||
|
||||
-- Generate PLRUs
|
||||
maybe_plrus: if NUM_WAYS > 1 generate
|
||||
begin
|
||||
plrus: for i in 0 to NUM_LINES-1 generate
|
||||
-- PLRU interface
|
||||
signal plru_acc : std_ulogic_vector(WAY_BITS-1 downto 0);
|
||||
signal plru_acc_en : std_ulogic;
|
||||
signal plru_out : std_ulogic_vector(WAY_BITS-1 downto 0);
|
||||
|
||||
begin
|
||||
plru : entity work.plru
|
||||
generic map (
|
||||
BITS => WAY_BITS
|
||||
)
|
||||
port map (
|
||||
clk => clk,
|
||||
rst => rst,
|
||||
acc => plru_acc,
|
||||
acc_en => plru_acc_en,
|
||||
lru => plru_out
|
||||
);
|
||||
|
||||
process(req_index, req_op, req_hit_way, plru_out)
|
||||
begin
|
||||
-- PLRU interface
|
||||
if (req_op = OP_LOAD_HIT or
|
||||
req_op = OP_STORE_HIT) and req_index = i then
|
||||
plru_acc_en <= '1';
|
||||
else
|
||||
plru_acc_en <= '0';
|
||||
end if;
|
||||
plru_acc <= std_ulogic_vector(to_unsigned(req_hit_way, WAY_BITS));
|
||||
plru_victim(i) <= plru_out;
|
||||
end process;
|
||||
end generate;
|
||||
end generate;
|
||||
|
||||
-- Cache request parsing and hit detection
|
||||
dcache_request : process(all)
|
||||
variable is_hit : std_ulogic;
|
||||
variable hit_way : way_t;
|
||||
variable op : op_t;
|
||||
variable tmp : std_ulogic_vector(63 downto 0);
|
||||
variable data : std_ulogic_vector(63 downto 0);
|
||||
variable opsel : std_ulogic_vector(3 downto 0);
|
||||
begin
|
||||
-- Extract line, row and tag from request
|
||||
req_index <= get_index(d_in.addr);
|
||||
req_row <= get_row(d_in.addr);
|
||||
req_tag <= get_tag(d_in.addr);
|
||||
|
||||
-- Test if pending request is a hit on any way
|
||||
hit_way := 0;
|
||||
is_hit := '0';
|
||||
for i in way_t loop
|
||||
if d_in.valid = '1' and cache_valids(req_index)(i) = '1' then
|
||||
if read_tag(i, cache_tags(req_index)) = req_tag then
|
||||
hit_way := i;
|
||||
is_hit := '1';
|
||||
end if;
|
||||
end if;
|
||||
end loop;
|
||||
|
||||
-- The way that matched on a hit
|
||||
req_hit_way <= hit_way;
|
||||
|
||||
-- Combine the request and cache his status to decide what
|
||||
-- operation needs to be done
|
||||
--
|
||||
opsel := d_in.valid & d_in.load & d_in.nc & is_hit;
|
||||
case opsel is
|
||||
when "1101" => op := OP_LOAD_HIT;
|
||||
when "1100" => op := OP_LOAD_MISS;
|
||||
when "1110" => op := OP_LOAD_NC;
|
||||
when "1001" => op := OP_STORE_HIT;
|
||||
when "1000" => op := OP_STORE_MISS;
|
||||
when "1010" => op := OP_STORE_MISS;
|
||||
when "1011" => op := OP_BAD;
|
||||
when "1111" => op := OP_BAD;
|
||||
when others => op := OP_NONE;
|
||||
end case;
|
||||
|
||||
req_op <= op;
|
||||
|
||||
-- XXX GENERATE ERRORS
|
||||
-- err_nc_collision <= '1' when op = OP_BAD else '0';
|
||||
|
||||
-- XXX Generate stalls
|
||||
-- stall_out <= r.state /= IDLE ?
|
||||
|
||||
end process;
|
||||
|
||||
-- Wire up wishbone request latch
|
||||
wishbone_out <= r.wb;
|
||||
|
||||
-- Writeback (loads and reg updates) & completion control logic
|
||||
--
|
||||
writeback_control: process(all)
|
||||
variable writeback_format : boolean;
|
||||
begin
|
||||
|
||||
-- The mux on d_out.write reg defaults to the normal load hit case.
|
||||
d_out.write_enable <= '0';
|
||||
d_out.valid <= '0';
|
||||
d_out.write_reg <= r.req_latch.write_reg;
|
||||
d_out.write_data <= cache_out(r.hit_way);
|
||||
d_out.write_len <= r.req_latch.length;
|
||||
d_out.write_shift <= r.req_latch.addr(2 downto 0);
|
||||
d_out.sign_extend <= r.req_latch.sign_extend;
|
||||
d_out.byte_reverse <= r.req_latch.byte_reverse;
|
||||
d_out.second_word <= '0';
|
||||
|
||||
-- By default writeback doesn't need formatting
|
||||
writeback_format := false;
|
||||
|
||||
-- We have a valid load or store hit or we just completed a slow
|
||||
-- op such as a load miss, a NC load or a store
|
||||
--
|
||||
if r.hit_load_valid = '1' or r.slow_valid = '1' then
|
||||
if r.req_latch.load = '1' then
|
||||
-- If it's a load, enable write back and enable formatting
|
||||
d_out.write_enable <= '1';
|
||||
writeback_format := true;
|
||||
|
||||
-- If it's a slow load (miss or NC) source it from the buffer
|
||||
if r.slow_valid = '1' then
|
||||
d_out.write_data <= r.slow_data;
|
||||
end if;
|
||||
|
||||
-- If it's a normal load (not a load with update), we complete
|
||||
-- now, otherwise we wait for the delayed update.
|
||||
--
|
||||
if r.req_latch.update = '0' then
|
||||
d_out.valid <= '1';
|
||||
end if;
|
||||
else
|
||||
-- It's a store, complete always
|
||||
d_out.valid <= '1';
|
||||
end if;
|
||||
|
||||
-- Sanity
|
||||
assert r.update_valid = '0' report "unexpected update_valid"
|
||||
severity FAILURE;
|
||||
end if;
|
||||
|
||||
-- We have a register update to do.
|
||||
if r.update_valid = '1' then
|
||||
d_out.write_enable <= '1';
|
||||
d_out.write_reg <= r.req_latch.update_reg;
|
||||
d_out.write_data <= r.req_latch.addr;
|
||||
|
||||
-- If it was a load, this completes the operation
|
||||
if r.req_latch.load = '1' then
|
||||
d_out.valid <= '1';
|
||||
end if;
|
||||
end if;
|
||||
|
||||
if not writeback_format then
|
||||
d_out.write_len <= "1000";
|
||||
d_out.write_shift <= "000";
|
||||
d_out.sign_extend <= '0';
|
||||
d_out.byte_reverse <= '0';
|
||||
end if;
|
||||
|
||||
end process;
|
||||
|
||||
-- Misc data & sel signals
|
||||
misc: process(d_in)
|
||||
begin
|
||||
-- Wishbone & BRAM write data formatting for stores (most of it already
|
||||
-- happens in loadstore1, this is the remaining sel generation and shifting)
|
||||
--
|
||||
store_data <= std_logic_vector(shift_left(unsigned(d_in.data),
|
||||
wishbone_data_shift(d_in.addr)));
|
||||
|
||||
-- Wishbone read and write and BRAM write sel bits generation
|
||||
bus_sel <= wishbone_data_sel(d_in.length, d_in.addr);
|
||||
end process;
|
||||
|
||||
-- Generate a cache RAM for each way. This handles the normal
|
||||
-- reads, writes from reloads and the special store-hit update
|
||||
-- path as well
|
||||
--
|
||||
rams: for i in 0 to NUM_WAYS-1 generate
|
||||
signal do_read : std_ulogic;
|
||||
signal rd_addr : std_ulogic_vector(ROW_BITS-1 downto 0);
|
||||
signal do_write : std_ulogic;
|
||||
signal wr_addr : std_ulogic_vector(ROW_BITS-1 downto 0);
|
||||
signal wr_data : std_ulogic_vector(wishbone_data_bits-1 downto 0);
|
||||
signal wr_sel : std_ulogic_vector(ROW_SIZE-1 downto 0);
|
||||
signal dout : cache_row_t;
|
||||
begin
|
||||
way: entity work.cache_ram
|
||||
generic map (
|
||||
ROW_BITS => ROW_BITS,
|
||||
WIDTH => wishbone_data_bits
|
||||
)
|
||||
port map (
|
||||
clk => clk,
|
||||
rd_en => do_read,
|
||||
rd_addr => rd_addr,
|
||||
rd_data => dout,
|
||||
wr_en => do_write,
|
||||
wr_sel => wr_sel,
|
||||
wr_addr => wr_addr,
|
||||
wr_data => wr_data
|
||||
);
|
||||
process(all)
|
||||
begin
|
||||
do_read <= '0';
|
||||
do_write <= '0';
|
||||
|
||||
-- Cache hit reads
|
||||
if req_op = OP_LOAD_HIT and req_hit_way = i then
|
||||
do_read <= '1';
|
||||
end if;
|
||||
rd_addr <= std_ulogic_vector(to_unsigned(req_row, ROW_BITS));
|
||||
cache_out(i) <= dout;
|
||||
|
||||
-- Write mux:
|
||||
--
|
||||
-- Defaults to wishbone read responses (cache refill),
|
||||
--
|
||||
wr_data <= wishbone_in.dat;
|
||||
wr_sel <= (others => '1');
|
||||
wr_addr <= std_ulogic_vector(to_unsigned(get_row(r.wb.adr), ROW_BITS));
|
||||
if r.state = RELOAD_WAIT_ACK and wishbone_in.ack = '1' and r.store_way = i then
|
||||
do_write <= '1';
|
||||
end if;
|
||||
|
||||
-- Alternatively, store-hit BRAM update case (exclusive from the above).
|
||||
if req_op = OP_STORE_HIT and req_hit_way = i then
|
||||
report "store_data:" & to_hstring(store_data);
|
||||
wr_addr <= std_ulogic_vector(to_unsigned(req_row, ROW_BITS));
|
||||
wr_data <= store_data;
|
||||
wr_sel <= bus_sel;
|
||||
do_write <= '1';
|
||||
end if;
|
||||
end process;
|
||||
end generate;
|
||||
|
||||
-- Cache hit synchronous machine for the easy case. This handles
|
||||
-- non-update form load hits.
|
||||
--
|
||||
dcache_fast_hit : process(clk)
|
||||
begin
|
||||
if rising_edge(clk) then
|
||||
-- On-cycle pulse values get reset on every cycle
|
||||
r.hit_load_valid <= '0';
|
||||
|
||||
-- If we have a request incoming, we have to latch it as d_in.valid
|
||||
-- is only set for a single cycle. It's up to the control logic to
|
||||
-- ensure we don't override an uncompleted request (for now we are
|
||||
-- single issue on load/stores so we are fine, later, we can generate
|
||||
-- a stall output if necessary).
|
||||
|
||||
if d_in.valid = '1' then
|
||||
r.req_latch <= d_in;
|
||||
|
||||
report "dcache op:" & op_t'image(req_op) &
|
||||
" addr:" & to_hstring(d_in.addr) &
|
||||
" upd:" & std_ulogic'image(d_in.update) &
|
||||
" nc:" & std_ulogic'image(d_in.nc) &
|
||||
" reg:" & to_hstring(d_in.write_reg) &
|
||||
" idx:" & integer'image(req_index) &
|
||||
" tag:" & to_hstring(req_tag) &
|
||||
" way: " & integer'image(req_hit_way);
|
||||
end if;
|
||||
|
||||
-- Fast path for load/store hits. Set signals for the writeback controls.
|
||||
if req_op = OP_LOAD_HIT then
|
||||
r.hit_way <= req_hit_way;
|
||||
r.hit_load_valid <= '1';
|
||||
end if;
|
||||
end if;
|
||||
end process;
|
||||
|
||||
-- Every other case is handled by this stage machine:
|
||||
--
|
||||
-- * Cache load miss/reload (in conjunction with "rams")
|
||||
-- * Load hits for update forms
|
||||
-- * Load hits for non-cachable forms
|
||||
-- * Stores (the collision case is handled in "rams")
|
||||
--
|
||||
-- All wishbone requests generation is done here
|
||||
--
|
||||
dcache_slow : process(clk)
|
||||
variable way : integer range 0 to NUM_WAYS-1;
|
||||
variable tagset : cache_tags_set_t;
|
||||
begin
|
||||
if rising_edge(clk) then
|
||||
-- On reset, clear all valid bits to force misses
|
||||
if rst = '1' then
|
||||
for i in index_t loop
|
||||
cache_valids(i) <= (others => '0');
|
||||
end loop;
|
||||
r.state <= IDLE;
|
||||
r.slow_valid <= '0';
|
||||
r.update_valid <= '0';
|
||||
r.wb.cyc <= '0';
|
||||
r.wb.stb <= '0';
|
||||
|
||||
-- Not useful normally but helps avoiding tons of sim warnings
|
||||
r.wb.adr <= (others => '0');
|
||||
else
|
||||
-- One cycle pulses reset
|
||||
r.slow_valid <= '0';
|
||||
r.update_valid <= '0';
|
||||
|
||||
-- We cannot currently process a new request when not idle
|
||||
assert req_op = OP_NONE or r.state = IDLE report "request " &
|
||||
op_t'image(req_op) & " while in state " & state_t'image(r.state)
|
||||
severity FAILURE;
|
||||
|
||||
-- Main state machine
|
||||
case r.state is
|
||||
when IDLE =>
|
||||
case req_op is
|
||||
when OP_LOAD_HIT =>
|
||||
-- We have a load with update hit, we need the delayed update cycle
|
||||
if d_in.update = '1' then
|
||||
r.state <= LOAD_UPDATE;
|
||||
end if;
|
||||
|
||||
when OP_LOAD_MISS =>
|
||||
-- Normal load cache miss, start the reload machine
|
||||
--
|
||||
-- First find a victim way from the PLRU
|
||||
--
|
||||
way := to_integer(unsigned(plru_victim(req_index)));
|
||||
|
||||
report "cache miss addr:" & to_hstring(d_in.addr) &
|
||||
" idx:" & integer'image(req_index) &
|
||||
" way:" & integer'image(way) &
|
||||
" tag:" & to_hstring(req_tag);
|
||||
|
||||
-- Force misses on that way while reloading that line
|
||||
cache_valids(req_index)(way) <= '0';
|
||||
|
||||
-- Store new tag in selected way
|
||||
for i in 0 to NUM_WAYS-1 loop
|
||||
if i = way then
|
||||
tagset := cache_tags(req_index);
|
||||
write_tag(i, tagset, req_tag);
|
||||
cache_tags(req_index) <= tagset;
|
||||
end if;
|
||||
end loop;
|
||||
|
||||
-- Keep track of our index and way for subsequent stores.
|
||||
r.store_index <= req_index;
|
||||
r.store_way <= way;
|
||||
|
||||
-- Prep for first wishbone read. We calculate the address of
|
||||
-- the start of the cache line
|
||||
--
|
||||
r.wb.adr <= d_in.addr(63 downto LINE_OFF_BITS) &
|
||||
(LINE_OFF_BITS-1 downto 0 => '0');
|
||||
r.wb.sel <= (others => '1');
|
||||
r.wb.we <= '0';
|
||||
r.wb.cyc <= '1';
|
||||
r.wb.stb <= '1';
|
||||
r.state <= RELOAD_WAIT_ACK;
|
||||
|
||||
when OP_LOAD_NC =>
|
||||
r.wb.sel <= bus_sel;
|
||||
r.wb.adr <= d_in.addr(63 downto 3) & "000";
|
||||
r.wb.cyc <= '1';
|
||||
r.wb.stb <= '1';
|
||||
r.wb.we <= '0';
|
||||
r.state <= NC_LOAD_WAIT_ACK;
|
||||
|
||||
when OP_STORE_HIT | OP_STORE_MISS =>
|
||||
-- For store-with-update do the register update
|
||||
if d_in.update = '1' then
|
||||
r.update_valid <= '1';
|
||||
end if;
|
||||
r.wb.sel <= bus_sel;
|
||||
r.wb.adr <= d_in.addr(63 downto 3) & "000";
|
||||
r.wb.dat <= store_data;
|
||||
r.wb.cyc <= '1';
|
||||
r.wb.stb <= '1';
|
||||
r.wb.we <= '1';
|
||||
r.state <= STORE_WAIT_ACK;
|
||||
|
||||
-- OP_NONE and OP_BAD do nothing
|
||||
when OP_NONE =>
|
||||
when OP_BAD =>
|
||||
end case;
|
||||
|
||||
when RELOAD_WAIT_ACK =>
|
||||
if wishbone_in.ack = '1' then
|
||||
-- Is this the data we were looking for ? Latch it so
|
||||
-- we can respond later. We don't currently complete the
|
||||
-- pending miss request immediately, we wait for the
|
||||
-- whole line to be loaded. The reason is that if we
|
||||
-- did, we would potentially get new requests in while
|
||||
-- not idle, which we don't currently know how to deal
|
||||
-- with.
|
||||
--
|
||||
if r.wb.adr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) =
|
||||
r.req_latch.addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) then
|
||||
r.slow_data <= wishbone_in.dat;
|
||||
end if;
|
||||
|
||||
-- That was the last word ? We are done
|
||||
if is_last_row(r.wb.adr) then
|
||||
cache_valids(r.store_index)(way) <= '1';
|
||||
r.wb.cyc <= '0';
|
||||
r.wb.stb <= '0';
|
||||
|
||||
-- Complete the load that missed. For load with update
|
||||
-- we also need to do the deferred update cycle.
|
||||
--
|
||||
r.slow_valid <= '1';
|
||||
if r.req_latch.load = '1' and r.req_latch.update = '1' then
|
||||
r.state <= LOAD_UPDATE;
|
||||
report "completing miss with load-update !";
|
||||
else
|
||||
r.state <= IDLE;
|
||||
report "completing miss !";
|
||||
end if;
|
||||
else
|
||||
-- Otherwise, calculate the next row address
|
||||
r.wb.adr <= next_row_addr(r.wb.adr);
|
||||
end if;
|
||||
end if;
|
||||
|
||||
when LOAD_UPDATE =>
|
||||
-- We need the extra cycle to complete a load with update
|
||||
r.update_valid <= '1';
|
||||
r.state <= IDLE;
|
||||
|
||||
when STORE_WAIT_ACK | NC_LOAD_WAIT_ACK =>
|
||||
if wishbone_in.ack = '1' then
|
||||
if r.state = NC_LOAD_WAIT_ACK then
|
||||
r.slow_data <= wishbone_in.dat;
|
||||
end if;
|
||||
r.slow_valid <= '1';
|
||||
r.wb.cyc <= '0';
|
||||
r.wb.stb <= '0';
|
||||
r.state <= IDLE;
|
||||
end if;
|
||||
end case;
|
||||
end if;
|
||||
end if;
|
||||
end process;
|
||||
end;
|
||||
@ -1,148 +0,0 @@
|
||||
library ieee;
|
||||
use ieee.std_logic_1164.all;
|
||||
use ieee.numeric_std.all;
|
||||
|
||||
library work;
|
||||
use work.common.all;
|
||||
use work.helpers.all;
|
||||
use work.wishbone_types.all;
|
||||
|
||||
-- 2 cycle LSU
|
||||
-- In this cycle we read or write any data and do sign extension and update if required.
|
||||
|
||||
entity loadstore2 is
|
||||
port (
|
||||
clk : in std_ulogic;
|
||||
|
||||
l_in : in Loadstore1ToLoadstore2Type;
|
||||
w_out : out Loadstore2ToWritebackType;
|
||||
|
||||
m_in : in wishbone_slave_out;
|
||||
m_out : out wishbone_master_out
|
||||
);
|
||||
end loadstore2;
|
||||
|
||||
architecture behave of loadstore2 is
|
||||
signal l_saved : Loadstore1ToLoadstore2Type;
|
||||
signal w_tmp : Loadstore2ToWritebackType;
|
||||
signal m_tmp : wishbone_master_out;
|
||||
signal dlength : std_ulogic_vector(3 downto 0);
|
||||
|
||||
type state_t is (IDLE, WAITING_FOR_READ_ACK, WAITING_FOR_WRITE_ACK);
|
||||
signal state : state_t := IDLE;
|
||||
|
||||
function length_to_sel(length : in std_logic_vector(3 downto 0)) return std_ulogic_vector is
|
||||
begin
|
||||
case length is
|
||||
when "0001" =>
|
||||
return "00000001";
|
||||
when "0010" =>
|
||||
return "00000011";
|
||||
when "0100" =>
|
||||
return "00001111";
|
||||
when "1000" =>
|
||||
return "11111111";
|
||||
when others =>
|
||||
return "00000000";
|
||||
end case;
|
||||
end function length_to_sel;
|
||||
|
||||
function wishbone_data_shift(address : in std_ulogic_vector(63 downto 0)) return natural is
|
||||
begin
|
||||
return to_integer(unsigned(address(2 downto 0))) * 8;
|
||||
end function wishbone_data_shift;
|
||||
|
||||
function wishbone_data_sel(size : in std_logic_vector(3 downto 0); address : in std_logic_vector(63 downto 0)) return std_ulogic_vector is
|
||||
begin
|
||||
return std_ulogic_vector(shift_left(unsigned(length_to_sel(size)), to_integer(unsigned(address(2 downto 0)))));
|
||||
end function wishbone_data_sel;
|
||||
begin
|
||||
|
||||
w_out <= w_tmp;
|
||||
m_out <= m_tmp;
|
||||
|
||||
loadstore2_0: process(clk)
|
||||
begin
|
||||
if rising_edge(clk) then
|
||||
|
||||
w_tmp.valid <= '0';
|
||||
w_tmp.write_enable <= '0';
|
||||
w_tmp.write_reg <= (others => '0');
|
||||
w_tmp.write_len <= "1000";
|
||||
w_tmp.write_shift <= "000";
|
||||
w_tmp.sign_extend <= '0';
|
||||
w_tmp.byte_reverse <= '0';
|
||||
w_tmp.second_word <= '0';
|
||||
|
||||
l_saved <= l_saved;
|
||||
|
||||
case_0: case state is
|
||||
when IDLE =>
|
||||
if l_in.valid = '1' then
|
||||
m_tmp <= wishbone_master_out_init;
|
||||
|
||||
m_tmp.sel <= wishbone_data_sel(l_in.length, l_in.addr);
|
||||
m_tmp.adr <= l_in.addr(63 downto 3) & "000";
|
||||
m_tmp.cyc <= '1';
|
||||
m_tmp.stb <= '1';
|
||||
|
||||
l_saved <= l_in;
|
||||
|
||||
if l_in.load = '1' then
|
||||
m_tmp.we <= '0';
|
||||
|
||||
-- Load with update instructions write two GPR destinations.
|
||||
-- We don't want the expense of two write ports, so make it
|
||||
-- single in the pipeline and write back the update GPR now
|
||||
-- and the load once we get the data back. We'll have to
|
||||
-- revisit this when loads can take exceptions.
|
||||
if l_in.update = '1' then
|
||||
w_tmp.write_enable <= '1';
|
||||
w_tmp.write_reg <= l_in.update_reg;
|
||||
w_tmp.write_data <= l_in.addr;
|
||||
end if;
|
||||
|
||||
state <= WAITING_FOR_READ_ACK;
|
||||
else
|
||||
m_tmp.we <= '1';
|
||||
|
||||
m_tmp.dat <= std_logic_vector(shift_left(unsigned(l_in.data), wishbone_data_shift(l_in.addr)));
|
||||
|
||||
assert l_in.sign_extend = '0' report "sign extension doesn't make sense for stores" severity failure;
|
||||
|
||||
state <= WAITING_FOR_WRITE_ACK;
|
||||
end if;
|
||||
end if;
|
||||
|
||||
when WAITING_FOR_READ_ACK =>
|
||||
if m_in.ack = '1' then
|
||||
-- write data to register file
|
||||
w_tmp.valid <= '1';
|
||||
w_tmp.write_enable <= '1';
|
||||
w_tmp.write_data <= m_in.dat;
|
||||
w_tmp.write_reg <= l_saved.write_reg;
|
||||
w_tmp.write_len <= l_saved.length;
|
||||
w_tmp.write_shift <= l_saved.addr(2 downto 0);
|
||||
w_tmp.sign_extend <= l_saved.sign_extend;
|
||||
w_tmp.byte_reverse <= l_saved.byte_reverse;
|
||||
|
||||
m_tmp <= wishbone_master_out_init;
|
||||
state <= IDLE;
|
||||
end if;
|
||||
|
||||
when WAITING_FOR_WRITE_ACK =>
|
||||
if m_in.ack = '1' then
|
||||
w_tmp.valid <= '1';
|
||||
if l_saved.update = '1' then
|
||||
w_tmp.write_enable <= '1';
|
||||
w_tmp.write_reg <= l_saved.update_reg;
|
||||
w_tmp.write_data <= l_saved.addr;
|
||||
end if;
|
||||
|
||||
m_tmp <= wishbone_master_out_init;
|
||||
state <= IDLE;
|
||||
end if;
|
||||
end case;
|
||||
end if;
|
||||
end process;
|
||||
end;
|
||||
Loading…
Reference in New Issue