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dcache: Add a dcache

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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>
jtag-port
Benjamin Herrenschmidt 5 years ago
parent 7b3df7cb05
commit b513f0fb48
9 changed files with 772 additions and 168 deletions
Show Stats Download Patch File Download Diff File

4
Makefile
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@ -17,7 +17,7 @@ common.o: decode_types.o
control.o: gpr_hazard.o cr_hazard.o control.o: gpr_hazard.o cr_hazard.o
sim_jtag.o: sim_jtag_socket.o sim_jtag.o: sim_jtag_socket.o
core_tb.o: common.o wishbone_types.o core.o soc.o sim_jtag.o core_tb.o: common.o wishbone_types.o core.o soc.o sim_jtag.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 loadstore1.o loadstore2.o multiply.o writeback.o core_debug.o divider.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 loadstore1.o dcache.o multiply.o writeback.o core_debug.o divider.o
core_debug.o: common.o core_debug.o: common.o
countzero.o: countzero.o:
countzero_tb.o: common.o glibc_random.o countzero.o countzero_tb.o: common.o glibc_random.o countzero.o
@ -37,9 +37,9 @@ plru.o:
plru_tb.o: plru.o plru_tb.o: plru.o
icache.o: common.o wishbone_types.o plru.o cache_ram.o icache.o: common.o wishbone_types.o plru.o cache_ram.o
icache_tb.o: common.o wishbone_types.o icache.o simple_ram_behavioural.o icache_tb.o: common.o wishbone_types.o icache.o simple_ram_behavioural.o
dcache.o: common.o wishbone_types.o plru.o cache_ram.o
insn_helpers.o: insn_helpers.o:
loadstore1.o: common.o helpers.o loadstore1.o: common.o helpers.o
loadstore2.o: common.o helpers.o wishbone_types.o
logical.o: decode_types.o logical.o: decode_types.o
multiply_tb.o: decode_types.o common.o glibc_random.o ppc_fx_insns.o multiply.o multiply_tb.o: decode_types.o common.o glibc_random.o ppc_fx_insns.o multiply.o
multiply.o: common.o decode_types.o multiply.o: common.o decode_types.o

8
common.vhdl
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@ -138,9 +138,10 @@ package common is
end record; end record;
constant Decode2ToLoadstore1Init : Decode2ToLoadstore1Type := (valid => '0', load => '0', byte_reverse => '0', sign_extend => '0', update => '0', others => (others => '0')); constant Decode2ToLoadstore1Init : Decode2ToLoadstore1Type := (valid => '0', load => '0', byte_reverse => '0', sign_extend => '0', update => '0', others => (others => '0'));


type Loadstore1ToLoadstore2Type is record type Loadstore1ToDcacheType is record
valid : std_ulogic; valid : std_ulogic;
load : std_ulogic; load : std_ulogic;
nc : std_ulogic;
addr : std_ulogic_vector(63 downto 0); addr : std_ulogic_vector(63 downto 0);
data : std_ulogic_vector(63 downto 0); data : std_ulogic_vector(63 downto 0);
write_reg : std_ulogic_vector(4 downto 0); write_reg : std_ulogic_vector(4 downto 0);
@ -151,7 +152,7 @@ package common is
update_reg : std_ulogic_vector(4 downto 0); update_reg : std_ulogic_vector(4 downto 0);
end record; end record;


type Loadstore2ToWritebackType is record type DcacheToWritebackType is record
valid : std_ulogic; valid : std_ulogic;
write_enable: std_ulogic; write_enable: std_ulogic;
write_reg : std_ulogic_vector(4 downto 0); write_reg : std_ulogic_vector(4 downto 0);
@ -162,7 +163,7 @@ package common is
byte_reverse : std_ulogic; byte_reverse : std_ulogic;
second_word : std_ulogic; second_word : std_ulogic;
end record; end record;
constant Loadstore2ToWritebackInit : Loadstore2ToWritebackType := (valid => '0', write_enable => '0', sign_extend => '0', byte_reverse => '0', second_word => '0', others => (others => '0')); constant DcacheToWritebackInit : DcacheToWritebackType := (valid => '0', write_enable => '0', sign_extend => '0', byte_reverse => '0', second_word => '0', others => (others => '0'));


type Execute1ToWritebackType is record type Execute1ToWritebackType is record
valid: std_ulogic; valid: std_ulogic;
@ -211,6 +212,7 @@ package common is
write_cr_data : std_ulogic_vector(31 downto 0); write_cr_data : std_ulogic_vector(31 downto 0);
end record; end record;
constant WritebackToCrFileInit : WritebackToCrFileType := (write_cr_enable => '0', others => (others => '0')); constant WritebackToCrFileInit : WritebackToCrFileType := (write_cr_enable => '0', others => (others => '0'));

end common; end common;


package body common is package body common is

19
core.vhdl
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@ -59,8 +59,8 @@ architecture behave of core is


-- load store signals -- load store signals
signal decode2_to_loadstore1: Decode2ToLoadstore1Type; signal decode2_to_loadstore1: Decode2ToLoadstore1Type;
signal loadstore1_to_loadstore2: Loadstore1ToLoadstore2Type; signal loadstore1_to_dcache: Loadstore1ToDcacheType;
signal loadstore2_to_writeback: Loadstore2ToWritebackType; signal dcache_to_writeback: DcacheToWritebackType;


-- multiply signals -- multiply signals
signal decode2_to_multiply: Decode2ToMultiplyType; signal decode2_to_multiply: Decode2ToMultiplyType;
@ -211,16 +211,17 @@ begin
port map ( port map (
clk => clk, clk => clk,
l_in => decode2_to_loadstore1, l_in => decode2_to_loadstore1,
l_out => loadstore1_to_loadstore2 l_out => loadstore1_to_dcache
); );


loadstore2_0: entity work.loadstore2 dcache_0: entity work.dcache
port map ( port map (
clk => clk, clk => clk,
l_in => loadstore1_to_loadstore2, rst => core_rst,
w_out => loadstore2_to_writeback, d_in => loadstore1_to_dcache,
m_in => wishbone_data_in, d_out => dcache_to_writeback,
m_out => wishbone_data_out wishbone_in => wishbone_data_in,
wishbone_out => wishbone_data_out
); );


multiply_0: entity work.multiply multiply_0: entity work.multiply
@ -242,7 +243,7 @@ begin
port map ( port map (
clk => clk, clk => clk,
e_in => execute1_to_writeback, e_in => execute1_to_writeback,
l_in => loadstore2_to_writeback, l_in => dcache_to_writeback,
m_in => multiply_to_writeback, m_in => multiply_to_writeback,
d_in => divider_to_writeback, d_in => divider_to_writeback,
w_out => writeback_to_register_file, w_out => writeback_to_register_file,

733
dcache.vhdl
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@ -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;

20
loadstore1.vhdl
Unescape Escape View File

@ -15,12 +15,12 @@ entity loadstore1 is


l_in : in Decode2ToLoadstore1Type; l_in : in Decode2ToLoadstore1Type;


l_out : out Loadstore1ToLoadstore2Type l_out : out Loadstore1ToDcacheType
); );
end loadstore1; end loadstore1;


architecture behave of loadstore1 is architecture behave of loadstore1 is
signal r, rin : Loadstore1ToLoadstore2Type; signal r, rin : Loadstore1ToDcacheType;
signal lsu_sum : std_ulogic_vector(63 downto 0); signal lsu_sum : std_ulogic_vector(63 downto 0);
begin begin
-- Calculate the address in the first cycle -- Calculate the address in the first cycle
@ -34,7 +34,7 @@ begin
end process; end process;


loadstore1_1: process(all) loadstore1_1: process(all)
variable v : Loadstore1ToLoadstore2Type; variable v : Loadstore1ToDcacheType;
begin begin
v := r; v := r;


@ -48,6 +48,20 @@ begin
v.update := l_in.update; v.update := l_in.update;
v.update_reg := l_in.update_reg; v.update_reg := l_in.update_reg;


-- XXX Temporary hack. Mark the op as non-cachable if the address
-- is the form 0xc-------
--
-- This will have to be replaced by a combination of implementing the
-- proper HV CI load/store instructions and having an MMU to get the I
-- bit otherwise.
if lsu_sum(31 downto 28) = "1100" then
v.nc := '1';
else
v.nc := '0';
end if;

-- XXX Do length_to_sel here ?

-- byte reverse stores in the first cycle -- byte reverse stores in the first cycle
if v.load = '0' and l_in.byte_reverse = '1' then if v.load = '0' and l_in.byte_reverse = '1' then
v.data := byte_reverse(l_in.data, to_integer(unsigned(l_in.length))); v.data := byte_reverse(l_in.data, to_integer(unsigned(l_in.length)));

148
loadstore2.vhdl
Unescape Escape View File

@ -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;

2
microwatt.core
Unescape Escape View File

@ -25,7 +25,7 @@ filesets:
- control.vhdl - control.vhdl
- execute1.vhdl - execute1.vhdl
- loadstore1.vhdl - loadstore1.vhdl
- loadstore2.vhdl - dcache.vhdl
- multiply.vhdl - multiply.vhdl
- divider.vhdl - divider.vhdl
- rotator.vhdl - rotator.vhdl

4
wishbone_types.vhdl
Unescape Escape View File

@ -4,16 +4,18 @@ use ieee.std_logic_1164.all;
package wishbone_types is package wishbone_types is
constant wishbone_addr_bits : integer := 64; constant wishbone_addr_bits : integer := 64;
constant wishbone_data_bits : integer := 64; constant wishbone_data_bits : integer := 64;
constant wishbone_sel_bits : integer := wishbone_data_bits/8;


subtype wishbone_addr_type is std_ulogic_vector(wishbone_addr_bits-1 downto 0); subtype wishbone_addr_type is std_ulogic_vector(wishbone_addr_bits-1 downto 0);
subtype wishbone_data_type is std_ulogic_vector(wishbone_data_bits-1 downto 0); subtype wishbone_data_type is std_ulogic_vector(wishbone_data_bits-1 downto 0);
subtype wishbone_sel_type is std_ulogic_vector(wishbone_sel_bits-1 downto 0);


type wishbone_master_out is record type wishbone_master_out is record
adr : wishbone_addr_type; adr : wishbone_addr_type;
dat : wishbone_data_type; dat : wishbone_data_type;
cyc : std_ulogic; cyc : std_ulogic;
stb : std_ulogic; stb : std_ulogic;
sel : std_ulogic_vector(7 downto 0); sel : wishbone_sel_type;
we : std_ulogic; we : std_ulogic;
end record; end record;
constant wishbone_master_out_init : wishbone_master_out := (cyc => '0', stb => '0', we => '0', others => (others => '0')); constant wishbone_master_out_init : wishbone_master_out := (cyc => '0', stb => '0', we => '0', others => (others => '0'));

2
writeback.vhdl
Unescape Escape View File

@ -11,7 +11,7 @@ entity writeback is
clk : in std_ulogic; clk : in std_ulogic;


e_in : in Execute1ToWritebackType; e_in : in Execute1ToWritebackType;
l_in : in Loadstore2ToWritebackType; l_in : in DcacheToWritebackType;
m_in : in MultiplyToWritebackType; m_in : in MultiplyToWritebackType;
d_in : in DividerToWritebackType; d_in : in DividerToWritebackType;



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