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dcache: Add wishbone pipelining support

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Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
pull/118/head
Benjamin Herrenschmidt 5 years ago
parent e638c3e8ae
commit d363daa692
1 changed files with 83 additions and 21 deletions
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104
dcache.vhdl
Unescape Escape View File

@ -187,6 +187,7 @@ architecture rtl of dcache is
state : state_t;
wb : wishbone_master_out;
store_way : way_t;
store_row : row_t;
store_index : index_t;
end record;

@ -213,6 +214,7 @@ architecture rtl of dcache is
signal req_hit_way : way_t;
signal req_tag : cache_tag_t;
signal req_op : op_t;
signal req_laddr : std_ulogic_vector(63 downto 0);

-- Cache RAM interface
type cache_ram_out_t is array(way_t) of cache_row_t;
@ -244,12 +246,21 @@ architecture rtl of dcache is
end;

-- Returns whether this is the last row of a line
function is_last_row(addr: wishbone_addr_type) return boolean is
function is_last_row_addr(addr: wishbone_addr_type) 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;

-- Returns whether this is the last row of a line
function is_last_row(row: row_t) return boolean is
variable row_v : std_ulogic_vector(ROW_BITS-1 downto 0);
constant ones : std_ulogic_vector(ROW_LINEBITS-1 downto 0) := (others => '1');
begin
row_v := std_ulogic_vector(to_unsigned(row, ROW_BITS));
return row_v(ROW_LINEBITS-1 downto 0) = ones;
end;

-- Return the address of the next row in the current cache line
function next_row_addr(addr: wishbone_addr_type) return std_ulogic_vector is
variable row_idx : std_ulogic_vector(ROW_LINEBITS-1 downto 0);
@ -263,6 +274,21 @@ architecture rtl of dcache is
return result;
end;

-- Return the next row in the current cache line. We use a dedicated
-- function in order to limit the size of the generated adder to be
-- only the bits within a cache line (3 bits with default settings)
--
function next_row(row: row_t) return row_t is
variable row_v : std_ulogic_vector(ROW_BITS-1 downto 0);
variable row_idx : std_ulogic_vector(ROW_LINEBITS-1 downto 0);
variable result : std_ulogic_vector(ROW_BITS-1 downto 0);
begin
row_v := std_ulogic_vector(to_unsigned(row, ROW_BITS));
row_idx := row_v(ROW_LINEBITS-1 downto 0);
row_v(ROW_LINEBITS-1 downto 0) := std_ulogic_vector(unsigned(row_idx) + 1);
return to_integer(unsigned(row_v));
end;

-- Get the tag value from the address
function get_tag(addr: std_ulogic_vector(63 downto 0)) return cache_tag_t is
begin
@ -381,6 +407,12 @@ begin
req_row <= get_row(d_in.addr);
req_tag <= get_tag(d_in.addr);

-- Calculate address of beginning of cache line, will be
-- used for cache miss processing if needed
--
req_laddr <= d_in.addr(63 downto LINE_OFF_BITS) &
(LINE_OFF_BITS-1 downto 0 => '0');

-- Test if pending request is a hit on any way
hit_way := 0;
is_hit := '0';
@ -573,7 +605,8 @@ begin
wr_data => wr_data
);
process(all)
variable tmp_adr : std_ulogic_vector(63 downto 0);
variable tmp_adr : std_ulogic_vector(63 downto 0);
variable reloading : boolean;
begin
-- Cache hit reads
do_read <= '1';
@ -596,17 +629,17 @@ begin
-- Otherwise, we might be doing a reload
wr_data <= wishbone_in.dat;
wr_sel <= (others => '1');
tmp_adr := (r1.wb.adr'left downto 0 => r1.wb.adr, others => '0');
wr_addr <= std_ulogic_vector(to_unsigned(get_row(tmp_adr), ROW_BITS));
wr_addr <= std_ulogic_vector(to_unsigned(r1.store_row, ROW_BITS));
end if;

-- The two actual write cases here
do_write <= '0';
if r1.state = RELOAD_WAIT_ACK and wishbone_in.ack = '1' and r1.store_way = i then
reloading := r1.state = RELOAD_WAIT_ACK;
if reloading and wishbone_in.ack = '1' and r1.store_way = i then
do_write <= '1';
end if;
if req_op = OP_STORE_HIT and req_hit_way = i then
assert r1.state /= RELOAD_WAIT_ACK report "Store hit while in state:" &
assert not reloading report "Store hit while in state:" &
state_t'image(r1.state)
severity FAILURE;
do_write <= '1';
@ -637,7 +670,7 @@ begin
-- single issue on load/stores so we are fine, later, we can generate
-- a stall output if necessary).

if d_in.valid = '1' then
if req_op /= OP_NONE then
r1.req <= d_in;

report "op:" & op_t'image(req_op) &
@ -672,7 +705,8 @@ begin
-- operates at stage 1.
--
dcache_slow : process(clk)
variable tagset : cache_tags_set_t;
variable tagset : cache_tags_set_t;
variable stbs_done : boolean;
begin
if rising_edge(clk) then
-- On reset, clear all valid bits to force misses
@ -731,16 +765,18 @@ begin
-- Keep track of our index and way for subsequent stores.
r1.store_index <= req_index;
r1.store_way <= replace_way;
r1.store_row <= get_row(req_laddr);

-- Prep for first wishbone read. We calculate the address of
-- the start of the cache line
-- the start of the cache line and start the WB cycle
--
r1.wb.adr <= d_in.addr(r1.wb.adr'left downto LINE_OFF_BITS) &
(LINE_OFF_BITS-1 downto 0 => '0');
r1.wb.adr <= req_laddr(r1.wb.adr'left downto 0);
r1.wb.sel <= (others => '1');
r1.wb.we <= '0';
r1.wb.cyc <= '1';
r1.wb.stb <= '1';

-- Track that we had one request sent
r1.state <= RELOAD_WAIT_ACK;

when OP_LOAD_NC =>
@ -770,6 +806,25 @@ begin
end case;

when RELOAD_WAIT_ACK =>
-- Requests are all sent if stb is 0
stbs_done := r1.wb.stb = '0';

-- If we are still sending requests, was one accepted ?
if wishbone_in.stall = '0' and not stbs_done then
-- That was the last word ? We are done sending. Clear
-- stb and set stbs_done so we can handle an eventual last
-- ack on the same cycle.
--
if is_last_row_addr(r1.wb.adr) then
r1.wb.stb <= '0';
stbs_done := true;
end if;

-- Calculate the next row address
r1.wb.adr <= next_row_addr(r1.wb.adr);
end if;

-- Incoming acks processing
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
@ -779,16 +834,17 @@ begin
-- not idle, which we don't currently know how to deal
-- with.
--
if r1.wb.adr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) =
r1.req.addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) then
if r1.store_row = get_row(r1.req.addr) then
r1.slow_data <= wishbone_in.dat;
end if;

-- That was the last word ? We are done
if is_last_row(r1.wb.adr) then
cache_valids(r1.store_index)(r1.store_way) <= '1';
-- Check for completion
if stbs_done and is_last_row(r1.store_row) then
-- Complete wishbone cycle
r1.wb.cyc <= '0';
r1.wb.stb <= '0';

-- Cache line is now valid
cache_valids(r1.store_index)(r1.store_way) <= '1';

-- Complete the load that missed. For load with update
-- we also need to do the deferred update cycle.
@ -801,10 +857,10 @@ begin
r1.state <= IDLE;
report "completing miss !";
end if;
else
-- Otherwise, calculate the next row address
r1.wb.adr <= next_row_addr(r1.wb.adr);
end if;

-- Increment store row counter
r1.store_row <= next_row(r1.store_row);
end if;

when LOAD_UPDATE =>
@ -816,7 +872,13 @@ begin
r1.state <= IDLE;

when STORE_WAIT_ACK | NC_LOAD_WAIT_ACK =>
if wishbone_in.ack = '1' then
-- Clear stb when slave accepted request
if wishbone_in.stall = '0' then
r1.wb.stb <= '0';
end if;

-- Got ack ? complete.
if wishbone_in.ack = '1' then
if r1.state = NC_LOAD_WAIT_ACK then
r1.slow_data <= wishbone_in.dat;
end if;

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