constant SET_SIZE_BITS : natural := LINE_OFF_BITS + INDEX_BITS;
-- TAG_BITS is the number of bits of the tag part of the address
constant TAG_BITS : natural := REAL_ADDR_BITS - SET_SIZE_BITS;
+ -- TAG_WIDTH is the width in bits of each way of the tag RAM
+ constant TAG_WIDTH : natural := TAG_BITS + 7 - ((TAG_BITS + 7) mod 8);
-- WAY_BITS is the number of bits to select a way
constant WAY_BITS : natural := log2(NUM_WAYS);
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;
+ subtype row_in_line_t is unsigned(ROW_LINEBITS-1 downto 0);
-- 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);
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;
+ constant TAG_RAM_WIDTH : natural := TAG_WIDTH * 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;
+ type row_per_line_valid_t is array(0 to ROW_PER_LINE - 1) of std_ulogic;
-- Storage. Hopefully "cache_rows" is a BRAM, the rest is LUTs
- signal cache_tags : cache_tags_array_t;
- signal cache_valids : cache_valids_t;
+ signal cache_tags : cache_tags_array_t;
+ signal cache_tag_set : cache_tags_set_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_BAD, -- NC cache hit, TLB miss, prot/RC failure
+ OP_STCX_FAIL, -- conditional store w/o reservation
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_TLB_ERR, -- TLB miss or protection/RC failure
OP_STORE_HIT, -- Store hitting cache
OP_STORE_MISS); -- Store missing cache
-- Cache state machine
type state_t is (IDLE, -- Normal load hit processing
RELOAD_WAIT_ACK, -- Cache reload wait ack
- FINISH_LD_MISS, -- Extra cycle after load miss
STORE_WAIT_ACK, -- Store wait ack
NC_LOAD_WAIT_ACK);-- Non-cachable load wait ack
end record;
signal r0 : reg_stage_0_t;
- signal r0_valid : std_ulogic;
-
+ signal r0_full : std_ulogic;
+
+ type mem_access_request_t is record
+ op : op_t;
+ dcbz : std_ulogic;
+ real_addr : std_ulogic_vector(REAL_ADDR_BITS - 1 downto 0);
+ data : std_ulogic_vector(63 downto 0);
+ byte_sel : std_ulogic_vector(7 downto 0);
+ hit_way : way_t;
+ repl_way : way_t;
+ end record;
+
-- First stage register, contains state for stage 1 of load hits
-- and for the state machine used by all other operations
--
type reg_stage_1_t is record
- -- Latch the complete request from ls1
- req : Loadstore1ToDcacheType;
- mmu_req : std_ulogic;
+ -- Info about the request
+ full : std_ulogic; -- have uncompleted request
+ mmu_req : std_ulogic; -- request is from MMU
+ req : mem_access_request_t;
-- Cache hit state
hit_way : way_t;
hit_load_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;
-
- -- Signal to complete a failed stcx.
- stcx_fail : std_ulogic;
+ -- 2-stage data buffer for data forwarded from writes to reads
+ forward_data1 : std_ulogic_vector(63 downto 0);
+ forward_data2 : std_ulogic_vector(63 downto 0);
+ forward_sel1 : std_ulogic_vector(7 downto 0);
+ forward_valid1 : std_ulogic;
+ forward_way1 : way_t;
+ forward_row1 : row_t;
+ use_forward1 : std_ulogic;
+ forward_sel : std_ulogic_vector(7 downto 0);
-- Cache miss state (reload state machine)
state : state_t;
+ dcbz : std_ulogic;
+ write_bram : std_ulogic;
+ write_tag : std_ulogic;
+ slow_valid : std_ulogic;
wb : wishbone_master_out;
+ reload_tag : cache_tag_t;
store_way : way_t;
store_row : row_t;
store_index : index_t;
+ end_row_ix : row_in_line_t;
+ rows_valid : row_per_line_valid_t;
+ acks_pending : unsigned(2 downto 0);
-- Signals to complete with error
error_done : std_ulogic;
cache_paradox : std_ulogic;
+ -- Signal to complete a failed stcx.
+ stcx_fail : std_ulogic;
+
-- completion signal for tlbie
tlbie_done : std_ulogic;
end record;
signal req_tag : cache_tag_t;
signal req_op : op_t;
signal req_data : std_ulogic_vector(63 downto 0);
- signal req_laddr : std_ulogic_vector(63 downto 0);
signal early_req_row : row_t;
signal set_rsrv : std_ulogic;
signal clear_rsrv : std_ulogic;
+ signal r0_valid : std_ulogic;
+ signal r0_stall : std_ulogic;
+
+ signal use_forward1_next : std_ulogic;
+ signal use_forward2_next : std_ulogic;
+
-- Cache RAM interface
type cache_ram_out_t is array(way_t) of cache_row_t;
signal cache_out : cache_ram_out_t;
signal perm_attr : perm_attr_t;
signal rc_ok : std_ulogic;
signal perm_ok : std_ulogic;
+ signal access_ok : std_ulogic;
-- TLB PLRU output interface
type tlb_plru_out_t is array(tlb_index_t) of std_ulogic_vector(TLB_WAY_BITS-1 downto 0);
--
-- Return the cache line index (tag index) for an address
- function get_index(addr: std_ulogic_vector(63 downto 0)) return index_t is
+ function get_index(addr: std_ulogic_vector) return index_t is
begin
return to_integer(unsigned(addr(SET_SIZE_BITS - 1 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
+ function get_row(addr: std_ulogic_vector) return row_t is
begin
return to_integer(unsigned(addr(SET_SIZE_BITS - 1 downto ROW_OFF_BITS)));
end;
+ -- Return the index of a row within a line
+ function get_row_of_line(row: row_t) return row_in_line_t is
+ variable row_v : unsigned(ROW_BITS-1 downto 0);
+ begin
+ row_v := to_unsigned(row, ROW_BITS);
+ return row_v(ROW_LINEBITS-1 downto 0);
+ end;
+
-- Returns whether this is the last row of a line
- function is_last_row_addr(addr: wishbone_addr_type) return boolean is
- constant ones : std_ulogic_vector(ROW_LINEBITS-1 downto 0) := (others => '1');
+ function is_last_row_addr(addr: wishbone_addr_type; last: row_in_line_t) return boolean is
begin
- return addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS) = ones;
+ return unsigned(addr(LINE_OFF_BITS-1 downto ROW_OFF_BITS)) = last;
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');
+ function is_last_row(row: row_t; last: row_in_line_t) return boolean is
begin
- row_v := std_ulogic_vector(to_unsigned(row, ROW_BITS));
- return row_v(ROW_LINEBITS-1 downto 0) = ones;
+ return get_row_of_line(row) = last;
end;
-- Return the address of the next row in the current cache line
end;
-- Get the tag value from the address
- function get_tag(addr: std_ulogic_vector(REAL_ADDR_BITS - 1 downto 0)) return cache_tag_t is
+ function get_tag(addr: std_ulogic_vector) return cache_tag_t is
begin
return addr(REAL_ADDR_BITS - 1 downto SET_SIZE_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;
+ return tagset(way * TAG_WIDTH + TAG_BITS - 1 downto way * TAG_WIDTH);
end;
-- Read a TLB tag from a TLB tag memory row
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;
+ assert SET_SIZE_BITS <= TLB_LG_PGSZ report "Set indexed by virtual address" severity FAILURE;
-- Latch the request in r0.req as long as we're not stalling
stage_0 : process(clk)
+ variable r : reg_stage_0_t;
begin
if rising_edge(clk) then
+ assert (d_in.valid and m_in.valid) = '0' report
+ "request collision loadstore vs MMU";
+ if m_in.valid = '1' then
+ r.req.valid := '1';
+ r.req.load := not (m_in.tlbie or m_in.tlbld);
+ r.req.dcbz := '0';
+ r.req.nc := '0';
+ r.req.reserve := '0';
+ r.req.virt_mode := '0';
+ r.req.priv_mode := '1';
+ r.req.addr := m_in.addr;
+ r.req.data := m_in.pte;
+ r.req.byte_sel := (others => '1');
+ r.tlbie := m_in.tlbie;
+ r.doall := m_in.doall;
+ r.tlbld := m_in.tlbld;
+ r.mmu_req := '1';
+ else
+ r.req := d_in;
+ r.tlbie := '0';
+ r.doall := '0';
+ r.tlbld := '0';
+ r.mmu_req := '0';
+ end if;
if rst = '1' then
- r0.req.valid <= '0';
- elsif stall_out = '0' then
- assert (d_in.valid and m_in.valid) = '0' report
- "request collision loadstore vs MMU";
- if m_in.valid = '1' then
- r0.req.valid <= '1';
- r0.req.load <= not (m_in.tlbie or m_in.tlbld);
- r0.req.dcbz <= '0';
- r0.req.nc <= '0';
- r0.req.reserve <= '0';
- r0.req.virt_mode <= '0';
- r0.req.priv_mode <= '1';
- r0.req.addr <= m_in.addr;
- r0.req.data <= m_in.pte;
- r0.req.byte_sel <= (others => '1');
- r0.tlbie <= m_in.tlbie;
- r0.doall <= m_in.doall;
- r0.tlbld <= m_in.tlbld;
- r0.mmu_req <= '1';
- else
- r0.req <= d_in;
- r0.tlbie <= '0';
- r0.doall <= '0';
- r0.tlbld <= '0';
- r0.mmu_req <= '0';
- end if;
+ r0_full <= '0';
+ elsif r1.full = '0' or r0_full = '0' then
+ r0 <= r;
+ r0_full <= r.req.valid;
end if;
end if;
end process;
-- we don't yet handle collisions between loadstore1 requests and MMU requests
m_out.stall <= '0';
- -- Hold off the request in r0 when stalling,
- -- and cancel it if we get an error in a previous request.
- r0_valid <= r0.req.valid and not stall_out and not r1.error_done;
+ -- Hold off the request in r0 when r1 has an uncompleted request
+ r0_stall <= r0_full and r1.full;
+ r0_valid <= r0_full and not r1.full;
+ stall_out <= r0_stall;
-- TLB
-- Operates in the second cycle on the request latched in r0.req.
variable addrbits : std_ulogic_vector(TLB_SET_BITS - 1 downto 0);
begin
if rising_edge(clk) then
- if stall_out = '1' then
- -- keep reading the same thing while stalled
- index := tlb_req_index;
+ if m_in.valid = '1' then
+ addrbits := m_in.addr(TLB_LG_PGSZ + TLB_SET_BITS - 1 downto TLB_LG_PGSZ);
else
- if m_in.valid = '1' then
- addrbits := m_in.addr(TLB_LG_PGSZ + TLB_SET_BITS - 1 downto TLB_LG_PGSZ);
- else
- addrbits := d_in.addr(TLB_LG_PGSZ + TLB_SET_BITS - 1 downto TLB_LG_PGSZ);
- end if;
- index := to_integer(unsigned(addrbits));
+ addrbits := d_in.addr(TLB_LG_PGSZ + TLB_SET_BITS - 1 downto TLB_LG_PGSZ);
+ end if;
+ index := to_integer(unsigned(addrbits));
+ -- If we have any op and the previous op isn't finished,
+ -- then keep the same output for next cycle.
+ if r0_stall = '0' then
+ tlb_valid_way <= dtlb_valids(index);
+ tlb_tag_way <= dtlb_tags(index);
+ tlb_pte_way <= dtlb_ptes(index);
end if;
- tlb_valid_way <= dtlb_valids(index);
- tlb_tag_way <= dtlb_tags(index);
- tlb_pte_way <= dtlb_ptes(index);
end if;
end process;
valid_ra <= tlb_hit or not r0.req.virt_mode;
if r0.req.virt_mode = '1' then
ra <= pte(REAL_ADDR_BITS - 1 downto TLB_LG_PGSZ) &
- r0.req.addr(TLB_LG_PGSZ - 1 downto 0);
+ r0.req.addr(TLB_LG_PGSZ - 1 downto ROW_OFF_BITS) &
+ (ROW_OFF_BITS-1 downto 0 => '0');
perm_attr <= extract_perm_attr(pte);
else
- ra <= r0.req.addr(REAL_ADDR_BITS - 1 downto 0);
+ ra <= r0.req.addr(REAL_ADDR_BITS - 1 downto ROW_OFF_BITS) &
+ (ROW_OFF_BITS-1 downto 0 => '0');
perm_attr <= real_mode_perm_attr;
end if;
end process;
end generate;
end generate;
+ -- Cache tag RAM read port
+ cache_tag_read : process(clk)
+ variable index : index_t;
+ begin
+ if rising_edge(clk) then
+ if r0_stall = '1' then
+ index := req_index;
+ elsif m_in.valid = '1' then
+ index := get_index(m_in.addr);
+ else
+ index := get_index(d_in.addr);
+ end if;
+ cache_tag_set <= cache_tags(index);
+ end if;
+ end process;
+
-- 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 opsel : std_ulogic_vector(2 downto 0);
- variable go : std_ulogic;
- variable nc : std_ulogic;
- variable s_hit : std_ulogic;
- variable s_tag : cache_tag_t;
- variable s_pte : tlb_pte_t;
- variable s_ra : std_ulogic_vector(REAL_ADDR_BITS - 1 downto 0);
- variable hit_set : std_ulogic_vector(TLB_NUM_WAYS - 1 downto 0);
+ variable is_hit : std_ulogic;
+ variable hit_way : way_t;
+ variable op : op_t;
+ variable opsel : std_ulogic_vector(2 downto 0);
+ variable go : std_ulogic;
+ variable nc : std_ulogic;
+ variable s_hit : std_ulogic;
+ variable s_tag : cache_tag_t;
+ variable s_pte : tlb_pte_t;
+ variable s_ra : std_ulogic_vector(REAL_ADDR_BITS - 1 downto 0);
+ variable hit_set : std_ulogic_vector(TLB_NUM_WAYS - 1 downto 0);
variable hit_way_set : hit_way_set_t;
+ variable rel_matches : std_ulogic_vector(TLB_NUM_WAYS - 1 downto 0);
+ variable rel_match : std_ulogic;
begin
-- Extract line, row and tag from request
req_index <= get_index(r0.req.addr);
req_row <= get_row(r0.req.addr);
req_tag <= get_tag(ra);
- -- Only do anything if not being stalled by stage 1
- go := r0_valid and not (r0.tlbie or r0.tlbld);
-
- -- Calculate address of beginning of cache line, will be
- -- used for cache miss processing if needed
- --
- req_laddr <= (63 downto REAL_ADDR_BITS => '0') &
- ra(REAL_ADDR_BITS - 1 downto LINE_OFF_BITS) &
- (LINE_OFF_BITS-1 downto 0 => '0');
+ go := r0_valid and not (r0.tlbie or r0.tlbld) and not r1.error_done;
-- Test if pending request is a hit on any way
-- In order to make timing in virtual mode, when we are using the TLB,
-- the TLB, and then decide later which match to use.
hit_way := 0;
is_hit := '0';
+ rel_match := '0';
if r0.req.virt_mode = '1' then
+ rel_matches := (others => '0');
for j in tlb_way_t loop
hit_way_set(j) := 0;
s_hit := '0';
s_tag := get_tag(s_ra);
for i in way_t loop
if go = '1' and cache_valids(req_index)(i) = '1' and
- read_tag(i, cache_tags(req_index)) = s_tag and
+ read_tag(i, cache_tag_set) = s_tag and
tlb_valid_way(j) = '1' then
hit_way_set(j) := i;
s_hit := '1';
end if;
end loop;
hit_set(j) := s_hit;
+ if s_tag = r1.reload_tag then
+ rel_matches(j) := '1';
+ end if;
end loop;
if tlb_hit = '1' then
is_hit := hit_set(tlb_hit_way);
hit_way := hit_way_set(tlb_hit_way);
+ rel_match := rel_matches(tlb_hit_way);
end if;
else
- s_tag := get_tag(r0.req.addr(REAL_ADDR_BITS - 1 downto 0));
+ s_tag := get_tag(r0.req.addr);
for i in way_t loop
if go = '1' and cache_valids(req_index)(i) = '1' and
- read_tag(i, cache_tags(req_index)) = s_tag then
+ read_tag(i, cache_tag_set) = s_tag then
hit_way := i;
is_hit := '1';
end if;
end loop;
+ if s_tag = r1.reload_tag then
+ rel_match := '1';
+ end if;
+ end if;
+
+ -- See if the request matches the line currently being reloaded
+ if r1.state = RELOAD_WAIT_ACK and req_index = r1.store_index and
+ rel_match = '1' then
+ -- For a store, consider this a hit even if the row isn't valid
+ -- since it will be by the time we perform the store.
+ -- For a load, check the appropriate row valid bit.
+ is_hit := not r0.req.load or r1.rows_valid(req_row mod ROW_PER_LINE);
+ hit_way := r1.store_way;
+ end if;
+
+ -- Whether to use forwarded data for a load or not
+ use_forward1_next <= '0';
+ if get_row(r1.req.real_addr) = req_row and r1.req.hit_way = hit_way then
+ -- Only need to consider r1.write_bram here, since if we are
+ -- writing refill data here, then we don't have a cache hit this
+ -- cycle on the line being refilled. (There is the possibility
+ -- that the load following the load miss that started the refill
+ -- could be to the old contents of the victim line, since it is a
+ -- couple of cycles after the refill starts before we see the
+ -- updated cache tag. In that case we don't use the bypass.)
+ use_forward1_next <= r1.write_bram;
+ end if;
+ use_forward2_next <= '0';
+ if r1.forward_row1 = req_row and r1.forward_way1 = hit_way then
+ use_forward2_next <= r1.forward_valid1;
end if;
-- The way that matched on a hit
rc_ok <= perm_attr.reference and (r0.req.load or perm_attr.changed);
perm_ok <= (r0.req.priv_mode or not perm_attr.priv) and
(perm_attr.wr_perm or (r0.req.load and perm_attr.rd_perm));
+ access_ok <= valid_ra and perm_ok and rc_ok;
-- Combine the request and cache hit status to decide what
-- operation needs to be done
nc := r0.req.nc or perm_attr.nocache;
op := OP_NONE;
if go = '1' then
- if valid_ra = '1' and rc_ok = '1' and perm_ok = '1' then
+ if access_ok = '0' then
+ op := OP_BAD;
+ elsif cancel_store = '1' then
+ op := OP_STCX_FAIL;
+ else
opsel := r0.req.load & nc & is_hit;
case opsel is
when "101" => op := OP_LOAD_HIT;
when "111" => op := OP_BAD;
when others => op := OP_NONE;
end case;
- else
- op := OP_TLB_ERR;
end if;
end if;
req_op <= op;
-- in the cases where we need to read the cache data BRAM.
-- If we're stalling then we need to keep reading the last
-- row requested.
- if stall_out = '0' then
+ if r0_stall = '0' then
if m_in.valid = '1' then
early_req_row <= get_row(m_in.addr);
else
-- Wire up wishbone request latch out of stage 1
wishbone_out <= r1.wb;
- -- Generate stalls from stage 1 state machine
- stall_out <= '1' when r1.state /= IDLE else '0';
-
-- Handle load-with-reservation and store-conditional instructions
reservation_comb: process(all)
begin
reservation_reg: process(clk)
begin
if rising_edge(clk) then
- if rst = '1' or clear_rsrv = '1' then
+ if rst = '1' then
reservation.valid <= '0';
- elsif set_rsrv = '1' then
- reservation.valid <= '1';
- reservation.addr <= r0.req.addr(63 downto LINE_OFF_BITS);
+ elsif r0_valid = '1' and access_ok = '1' then
+ if clear_rsrv = '1' then
+ reservation.valid <= '0';
+ elsif set_rsrv = '1' then
+ reservation.valid <= '1';
+ reservation.addr <= r0.req.addr(63 downto LINE_OFF_BITS);
+ end if;
end if;
end if;
end process;
-- Return data for loads & completion control logic
--
writeback_control: process(all)
+ variable data_out : std_ulogic_vector(63 downto 0);
+ variable data_fwd : std_ulogic_vector(63 downto 0);
+ variable j : integer;
begin
+ -- Use the bypass if are reading the row that was written 1 or 2 cycles
+ -- ago, including for the slow_valid = 1 case (i.e. completing a load
+ -- miss or a non-cacheable load).
+ if r1.use_forward1 = '1' then
+ data_fwd := r1.forward_data1;
+ else
+ data_fwd := r1.forward_data2;
+ end if;
+ data_out := cache_out(r1.hit_way);
+ for i in 0 to 7 loop
+ j := i * 8;
+ if r1.forward_sel(i) = '1' then
+ data_out(j + 7 downto j) := data_fwd(j + 7 downto j);
+ end if;
+ end loop;
- -- The mux on d_out.data defaults to the normal load hit case.
d_out.valid <= '0';
- d_out.data <= cache_out(r1.hit_way);
+ d_out.data <= data_out;
d_out.store_done <= '0';
d_out.error <= '0';
d_out.cache_paradox <= '0';
-- Outputs to MMU
m_out.done <= r1.tlbie_done;
m_out.err <= '0';
- m_out.data <= cache_out(r1.hit_way);
+ m_out.data <= data_out;
-- 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
-- Request came from loadstore1...
-- Load hit case is the standard path
if r1.hit_load_valid = '1' then
- report "completing load hit";
+ report "completing load hit data=" & to_hstring(data_out);
d_out.valid <= '1';
end if;
-- Slow ops (load miss, NC, stores)
if r1.slow_valid = '1' then
- -- If it's a load, enable register writeback and switch
- -- mux accordingly
- --
- if r1.req.load then
- -- Read data comes from the slow data latch
- d_out.data <= r1.slow_data;
- end if;
d_out.store_done <= '1';
-
- report "completing store or load miss";
+ report "completing store or load miss data=" & to_hstring(data_out);
d_out.valid <= '1';
end if;
-- Slow ops (i.e. load miss)
if r1.slow_valid = '1' then
- -- Read data comes from the slow data latch
- m_out.data <= r1.slow_data;
report "completing MMU load miss, data=" & to_hstring(m_out.data);
m_out.done <= '1';
end if;
wr_data => wr_data
);
process(all)
- variable tmp_adr : std_ulogic_vector(63 downto 0);
- variable reloading : boolean;
begin
-- Cache hit reads
do_read <= '1';
-- Defaults to wishbone read responses (cache refill),
--
-- For timing, the mux on wr_data/sel/addr is not dependent on anything
- -- other than the current state. Only the do_write signal is.
+ -- other than the current state.
--
- if r1.state = IDLE then
- -- In IDLE state, the only write path is the store-hit update case
- wr_addr <= std_ulogic_vector(to_unsigned(req_row, ROW_BITS));
- wr_data <= r0.req.data;
- wr_sel <= r0.req.byte_sel;
+ wr_sel_m <= (others => '0');
+
+ do_write <= '0';
+ if r1.write_bram = '1' then
+ -- Write store data to BRAM. This happens one cycle after the
+ -- store is in r0.
+ wr_data <= r1.req.data;
+ wr_sel <= r1.req.byte_sel;
+ wr_addr <= std_ulogic_vector(to_unsigned(get_row(r1.req.real_addr), ROW_BITS));
+ if i = r1.req.hit_way then
+ do_write <= '1';
+ end if;
else
-- Otherwise, we might be doing a reload or a DCBZ
- if r1.req.dcbz = '1' then
+ if r1.dcbz = '1' then
wr_data <= (others => '0');
else
wr_data <= wishbone_in.dat;
end if;
- wr_sel <= (others => '1');
- wr_addr <= std_ulogic_vector(to_unsigned(r1.store_row, ROW_BITS));
- end if;
+ wr_addr <= std_ulogic_vector(to_unsigned(r1.store_row, ROW_BITS));
+ wr_sel <= (others => '1');
- -- The two actual write cases here
- do_write <= '0';
- 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 and cancel_store = '0' and
- r0.req.dcbz = '0' then
- assert not reloading report "Store hit while in state:" &
- state_t'image(r1.state)
- severity FAILURE;
- do_write <= '1';
+ if r1.state = RELOAD_WAIT_ACK and wishbone_in.ack = '1' and r1.store_way = i then
+ do_write <= '1';
+ end if;
end if;
-- Mask write selects with do_write since BRAM doesn't
-- have a global write-enable
- for i in 0 to ROW_SIZE-1 loop
- wr_sel_m(i) <= wr_sel(i) and do_write;
- end loop;
+ if do_write = '1' then
+ wr_sel_m <= wr_sel;
+ end if;
end process;
end generate;
dcache_fast_hit : process(clk)
begin
if rising_edge(clk) then
- -- If we have a request incoming, we have to latch it as r0.req.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 req_op /= OP_NONE and stall_out = '0' then
- r1.req <= r0.req;
- r1.mmu_req <= r0.mmu_req;
+ if req_op /= OP_NONE then
report "op:" & op_t'image(req_op) &
" addr:" & to_hstring(r0.req.addr) &
" nc:" & std_ulogic'image(r0.req.nc) &
" tag:" & to_hstring(req_tag) &
" way: " & integer'image(req_hit_way);
end if;
+ if r0_valid = '1' then
+ r1.mmu_req <= r0.mmu_req;
+ end if;
- -- Fast path for load/store hits. Set signals for the writeback controls.
+ -- Fast path for load/store hits. Set signals for the writeback controls.
if req_op = OP_LOAD_HIT then
r1.hit_way <= req_hit_way;
r1.hit_load_valid <= '1';
r1.hit_load_valid <= '0';
end if;
- if req_op = OP_TLB_ERR then
+ if req_op = OP_BAD then
report "Signalling ld/st error valid_ra=" & std_ulogic'image(valid_ra) &
" rc_ok=" & std_ulogic'image(rc_ok) & " perm_ok=" & std_ulogic'image(perm_ok);
r1.error_done <= '1';
- r1.cache_paradox <= '0';
- elsif req_op = OP_BAD then
- report "Signalling cache paradox";
- r1.error_done <= '1';
- r1.cache_paradox <= '1';
+ r1.cache_paradox <= access_ok;
else
r1.error_done <= '0';
r1.cache_paradox <= '0';
end if;
+ if req_op = OP_STCX_FAIL then
+ r1.stcx_fail <= '1';
+ else
+ r1.stcx_fail <= '0';
+ end if;
+
-- complete tlbies and TLB loads in the third cycle
r1.tlbie_done <= r0_valid and (r0.tlbie or r0.tlbld);
end if;
end process;
--
- -- Every other case is handled by this state machine:
+ -- Memory accesses are handled by this state machine:
--
-- * Cache load miss/reload (in conjunction with "rams")
-- * Load hits for non-cachable forms
-- operates at stage 1.
--
dcache_slow : process(clk)
- variable tagset : cache_tags_set_t;
variable stbs_done : boolean;
+ variable req : mem_access_request_t;
+ variable acks : unsigned(2 downto 0);
begin
if rising_edge(clk) then
+ r1.use_forward1 <= use_forward1_next;
+ r1.forward_sel <= (others => '0');
+ if use_forward1_next = '1' then
+ r1.forward_sel <= r1.req.byte_sel;
+ elsif use_forward2_next = '1' then
+ r1.forward_sel <= r1.forward_sel1;
+ end if;
+
+ r1.forward_data2 <= r1.forward_data1;
+ if r1.write_bram = '1' then
+ r1.forward_data1 <= r1.req.data;
+ r1.forward_sel1 <= r1.req.byte_sel;
+ r1.forward_way1 <= r1.req.hit_way;
+ r1.forward_row1 <= get_row(r1.req.real_addr);
+ r1.forward_valid1 <= '1';
+ else
+ if r1.dcbz = '1' then
+ r1.forward_data1 <= (others => '0');
+ else
+ r1.forward_data1 <= wishbone_in.dat;
+ end if;
+ r1.forward_sel1 <= (others => '1');
+ r1.forward_way1 <= r1.store_way;
+ r1.forward_row1 <= r1.store_row;
+ r1.forward_valid1 <= '0';
+ end if;
+
-- 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;
r1.state <= IDLE;
+ r1.full <= '0';
r1.slow_valid <= '0';
r1.wb.cyc <= '0';
r1.wb.stb <= '0';
else
-- One cycle pulses reset
r1.slow_valid <= '0';
- r1.stcx_fail <= '0';
+ r1.write_bram <= '0';
+
+ if r1.write_tag = '1' then
+ -- Store new tag in selected way
+ for i in 0 to NUM_WAYS-1 loop
+ if i = r1.store_way then
+ cache_tags(r1.store_index)((i + 1) * TAG_WIDTH - 1 downto i * TAG_WIDTH) <=
+ (TAG_WIDTH - 1 downto TAG_BITS => '0') & r1.reload_tag;
+ end if;
+ end loop;
+ r1.write_tag <= '0';
+ end if;
+
+ -- Take request from r1.req if there is one there,
+ -- else from req_op, ra, etc.
+ if r1.full = '1' then
+ req := r1.req;
+ else
+ req.op := req_op;
+ req.dcbz := r0.req.dcbz;
+ req.real_addr := ra;
+ req.data := r0.req.data;
+ req.byte_sel := r0.req.byte_sel;
+ req.hit_way := req_hit_way;
+ req.repl_way := replace_way;
+
+ -- Store the incoming request from r0, if it is a slow request
+ -- Note that r1.full = 1 implies req_op = OP_NONE
+ if req_op = OP_LOAD_MISS or req_op = OP_LOAD_NC or
+ req_op = OP_STORE_MISS or req_op = OP_STORE_HIT then
+ r1.req <= req;
+ r1.full <= '1';
+ end if;
+ end if;
-- Main state machine
case r1.state is
when IDLE =>
- case req_op is
+ r1.wb.adr <= req.real_addr(r1.wb.adr'left downto 0);
+ r1.dcbz <= '0';
+
+ -- Keep track of our index and way for subsequent stores.
+ r1.store_index <= get_index(req.real_addr);
+ r1.store_row <= get_row(req.real_addr);
+ r1.end_row_ix <= get_row_of_line(get_row(req.real_addr)) - 1;
+ r1.reload_tag <= get_tag(req.real_addr);
+
+ if req.op = OP_STORE_HIT then
+ r1.store_way <= req.hit_way;
+ else
+ r1.store_way <= req.repl_way;
+ end if;
+
+ -- Reset per-row valid bits, ready for handling OP_LOAD_MISS
+ for i in 0 to ROW_PER_LINE - 1 loop
+ r1.rows_valid(i) <= '0';
+ end loop;
+
+ case req.op is
when OP_LOAD_HIT =>
-- stay in IDLE state
when OP_LOAD_MISS =>
-- Normal load cache miss, start the reload machine
--
- report "cache miss addr:" & to_hstring(r0.req.addr) &
- " idx:" & integer'image(req_index) &
- " way:" & integer'image(replace_way) &
- " tag:" & to_hstring(req_tag);
-
- -- Force misses on that way while reloading that line
- cache_valids(req_index)(replace_way) <= '0';
-
- -- Store new tag in selected way
- for i in 0 to NUM_WAYS-1 loop
- if i = replace_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.
- 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 and start the WB cycle
- --
- r1.wb.adr <= req_laddr(r1.wb.adr'left downto 0);
+ report "cache miss real addr:" & to_hstring(req.real_addr) &
+ " idx:" & integer'image(get_index(req.real_addr)) &
+ " way:" & integer'image(req.repl_way) &
+ " tag:" & to_hstring(get_tag(req.real_addr));
+
+ -- Start the wishbone cycle
r1.wb.sel <= (others => '1');
r1.wb.we <= '0';
r1.wb.cyc <= '1';
-- Track that we had one request sent
r1.state <= RELOAD_WAIT_ACK;
+ r1.write_tag <= '1';
when OP_LOAD_NC =>
- r1.wb.sel <= r0.req.byte_sel;
- r1.wb.adr <= ra(r1.wb.adr'left downto 3) & "000";
+ r1.wb.sel <= req.byte_sel;
r1.wb.cyc <= '1';
r1.wb.stb <= '1';
r1.wb.we <= '0';
r1.state <= NC_LOAD_WAIT_ACK;
when OP_STORE_HIT | OP_STORE_MISS =>
- if r0.req.dcbz = '0' then
- r1.wb.sel <= r0.req.byte_sel;
- r1.wb.adr <= ra(r1.wb.adr'left downto 3) & "000";
- r1.wb.dat <= r0.req.data;
- if cancel_store = '0' then
- r1.wb.cyc <= '1';
- r1.wb.stb <= '1';
- r1.wb.we <= '1';
- r1.state <= STORE_WAIT_ACK;
- else
- r1.stcx_fail <= '1';
- r1.state <= IDLE;
+ if req.dcbz = '0' then
+ r1.wb.sel <= req.byte_sel;
+ r1.wb.dat <= req.data;
+ r1.state <= STORE_WAIT_ACK;
+ r1.acks_pending <= to_unsigned(1, 3);
+ r1.full <= '0';
+ r1.slow_valid <= '1';
+ if req.op = OP_STORE_HIT then
+ r1.write_bram <= '1';
end if;
else
-- dcbz is handled much like a load miss except
-- that we are writing to memory instead of reading
- r1.store_index <= req_index;
- r1.store_row <= get_row(req_laddr);
-
- if req_op = OP_STORE_HIT then
- r1.store_way <= req_hit_way;
- else
- r1.store_way <= replace_way;
-
- -- Force misses on the victim way while zeroing
- cache_valids(req_index)(replace_way) <= '0';
-
- -- Store new tag in selected way
- for i in 0 to NUM_WAYS-1 loop
- if i = replace_way then
- tagset := cache_tags(req_index);
- write_tag(i, tagset, req_tag);
- cache_tags(req_index) <= tagset;
- end if;
- end loop;
- end if;
- -- Set up for wishbone writes
- r1.wb.adr <= req_laddr(r1.wb.adr'left downto 0);
+ -- Start the wishbone writes
r1.wb.sel <= (others => '1');
- r1.wb.we <= '1';
r1.wb.dat <= (others => '0');
- r1.wb.cyc <= '1';
- r1.wb.stb <= '1';
-- Handle the rest like a load miss
r1.state <= RELOAD_WAIT_ACK;
+ r1.write_tag <= '1';
+ r1.dcbz <= '1';
end if;
+ r1.wb.we <= '1';
+ r1.wb.cyc <= '1';
+ r1.wb.stb <= '1';
-- OP_NONE and OP_BAD do nothing
- -- OP_BAD was handled above already
+ -- OP_BAD & OP_STCX_FAIL were handled above already
when OP_NONE =>
when OP_BAD =>
- when OP_TLB_ERR =>
+ when OP_STCX_FAIL =>
end case;
- when RELOAD_WAIT_ACK =>
- -- Requests are all sent if stb is 0
+ 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 ?
-- 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
+ if is_last_row_addr(r1.wb.adr, r1.end_row_ix) then
r1.wb.stb <= '0';
stbs_done := true;
end if;
end if;
-- Incoming acks processing
+ r1.forward_valid1 <= wishbone_in.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 r1.store_row = get_row(r1.req.addr) and r1.req.dcbz = '0' then
- r1.slow_data <= wishbone_in.dat;
+ r1.rows_valid(r1.store_row mod ROW_PER_LINE) <= '1';
+ -- If this is the data we were looking for, we can
+ -- complete the request next cycle.
+ -- Compare the whole address in case the request in
+ -- r1.req is not the one that started this refill.
+ if r1.full = '1' and
+ ((r1.dcbz = '1' and r1.req.dcbz = '1') or
+ (r1.dcbz = '0' and r1.req.op = OP_LOAD_MISS)) and
+ r1.store_row = get_row(r1.req.real_addr) and
+ r1.reload_tag = get_tag(r1.req.real_addr) then
+ r1.full <= '0';
+ r1.slow_valid <= '1';
+ r1.forward_sel <= (others => '1');
+ r1.use_forward1 <= '1';
end if;
-- Check for completion
- if stbs_done and is_last_row(r1.store_row) then
+ if stbs_done and is_last_row(r1.store_row, r1.end_row_ix) then
-- Complete wishbone cycle
r1.wb.cyc <= '0';
-- Cache line is now valid
cache_valids(r1.store_index)(r1.store_way) <= '1';
- -- Don't complete and go idle until next cycle, in
- -- case the next request is for the last dword of
- -- the cache line we just loaded.
- r1.state <= FINISH_LD_MISS;
+ r1.state <= IDLE;
end if;
-- Increment store row counter
r1.store_row <= next_row(r1.store_row);
end if;
- when FINISH_LD_MISS =>
- -- Write back the load data that we got
- r1.slow_valid <= '1';
- r1.state <= IDLE;
- report "completing miss !";
+ when STORE_WAIT_ACK =>
+ stbs_done := r1.wb.stb = '0';
+ acks := r1.acks_pending;
+ -- Clear stb when slave accepted request
+ if wishbone_in.stall = '0' then
+ -- See if there is another store waiting to be done
+ -- which is in the same real page.
+ -- Using r1.req rather than req here limits us to one
+ -- store every two cycles, but helps timing in that we
+ -- don't depend on req_op or ra.
+ if r1.full = '1' and acks < 7 and
+ (r1.req.op = OP_STORE_MISS or r1.req.op = OP_STORE_HIT) and
+ (r1.req.real_addr(r1.wb.adr'left downto TLB_LG_PGSZ) =
+ r1.wb.adr(r1.wb.adr'left downto TLB_LG_PGSZ)) then
+ r1.wb.adr <= r1.req.real_addr(r1.wb.adr'left downto 0);
+ r1.wb.dat <= r1.req.data;
+ r1.wb.sel <= r1.req.byte_sel;
+ r1.wb.stb <= '1';
+ stbs_done := false;
+ if r1.req.op = OP_STORE_HIT then
+ r1.write_bram <= '1';
+ end if;
+ r1.full <= '0';
+ r1.slow_valid <= '1';
+ acks := acks + 1;
+ else
+ r1.wb.stb <= '0';
+ stbs_done := true;
+ end if;
+ end if;
+
+ -- Got ack ? See if complete.
+ if wishbone_in.ack = '1' then
+ if stbs_done and acks = 1 then
+ r1.state <= IDLE;
+ r1.wb.cyc <= '0';
+ r1.wb.stb <= '0';
+ end if;
+ acks := acks - 1;
+ end if;
+ r1.acks_pending <= acks;
- when STORE_WAIT_ACK | NC_LOAD_WAIT_ACK =>
+ when NC_LOAD_WAIT_ACK =>
-- Clear stb when slave accepted request
if wishbone_in.stall = '0' then
r1.wb.stb <= '0';
-- 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;
r1.state <= IDLE;
+ r1.full <= '0';
r1.slow_valid <= '1';
+ r1.forward_sel <= (others => '1');
+ r1.use_forward1 <= '1';
r1.wb.cyc <= '0';
r1.wb.stb <= '0';
end if;
projects / microwatt.git / commitdiff