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icache: Reduce metavalue warnings

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As in dcache, this changes most signals declared with integer type to
be unsigned bit vectors instead.  Some code has been rearranged to do
to_integer() or equality comparisons only when the relevant signals
should be well defined.  Non-fatal asserts have been sprinkled
throughout to assist with determining the cause of warnings from
library functions (primarily NUMERIC_STD.TO_INTEGER and
NUMERIC_STD."=").

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/396/head
Paul Mackerras 2 years ago
parent 6fe9dc9640
commit 221a7b3df0
1 changed files with 79 additions and 77 deletions
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156
icache.vhdl
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@ -4,9 +4,7 @@
-- TODO (in no specific order):
--
-- * Add debug interface to inspect cache content
-- * Add snoop/invalidate path
-- * Add multi-hit error detection
-- * Pipelined bus interface (wb or axi)
-- * Maybe add parity ? There's a few bits free in each BRAM row on Xilinx
-- * Add optimization: service hits on partially loaded lines
-- * Add optimization: (maybe) interrupt reload on fluch/redirect
@ -119,9 +117,11 @@ architecture rtl of icache is
-- .. |-----| | INDEX_BITS (5)
-- .. --------| | TAG_BITS (53)

subtype row_t is integer range 0 to BRAM_ROWS-1;
subtype row_t is unsigned(ROW_BITS-1 downto 0);
subtype index_t is integer range 0 to NUM_LINES-1;
subtype index_sig_t is unsigned(INDEX_BITS-1 downto 0);
subtype way_t is integer range 0 to NUM_WAYS-1;
subtype way_sig_t is unsigned(WAY_BITS-1 downto 0);
subtype row_in_line_t is unsigned(ROW_LINEBITS-1 downto 0);

-- We store a pre-decoded 10-bit insn_code along with the bottom 26 bits of
@ -187,7 +187,7 @@ architecture rtl of icache is

type reg_internal_t is record
-- Cache hit state (Latches for 1 cycle BRAM access)
hit_way : way_t;
hit_way : way_sig_t;
hit_nia : std_ulogic_vector(63 downto 0);
hit_smark : std_ulogic;
hit_valid : std_ulogic;
@ -196,8 +196,8 @@ architecture rtl of icache is
-- Cache miss state (reload state machine)
state : state_t;
wb : wishbone_master_out;
store_way : way_t;
store_index : index_t;
store_way : way_sig_t;
store_index : index_sig_t;
recv_row : row_t;
recv_valid : std_ulogic;
store_row : row_t;
@ -215,9 +215,9 @@ architecture rtl of icache is
signal ev : IcacheEventType;

-- Async signals on incoming request
signal req_index : index_t;
signal req_index : index_sig_t;
signal req_row : row_t;
signal req_hit_way : way_t;
signal req_hit_way : way_sig_t;
signal req_tag : cache_tag_t;
signal req_is_hit : std_ulogic;
signal req_is_miss : std_ulogic;
@ -237,33 +237,30 @@ architecture rtl of icache is
-- 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;
signal replace_way : way_t;

-- Memory write snoop signals
signal snoop_valid : std_ulogic;
signal snoop_index : index_t;
signal snoop_index : index_sig_t;
signal snoop_hits : cache_way_valids_t;

signal log_insn : std_ulogic_vector(35 downto 0);

-- Return the cache line index (tag index) for an address
function get_index(addr: std_ulogic_vector) return index_t is
function get_index(addr: std_ulogic_vector) return index_sig_t is
begin
return to_integer(unsigned(addr(SET_SIZE_BITS - 1 downto LINE_OFF_BITS)));
return 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) return row_t is
begin
return to_integer(unsigned(addr(SET_SIZE_BITS - 1 downto ROW_OFF_BITS)));
return 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);
return row(ROW_LINEBITS-1 downto 0);
end;

-- Returns whether this is the last row of a line
@ -298,13 +295,13 @@ architecture rtl of icache is
--
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 row_idx : unsigned(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));
row_v := std_ulogic_vector(row);
row_idx := row(ROW_LINEBITS-1 downto 0);
row_v(ROW_LINEBITS-1 downto 0) := std_ulogic_vector(row_idx + 1);
return unsigned(row_v);
end;

-- Read the instruction word for the given address in the current cache row
@ -312,6 +309,7 @@ architecture rtl of icache is
data: cache_row_t) return std_ulogic_vector is
variable word: integer range 0 to INSN_PER_ROW-1;
begin
assert not is_X(addr) severity failure;
word := to_integer(unsigned(addr(INSN_BITS+2-1 downto 2)));
return data(word * ICWORDLEN + ICWORDLEN - 1 downto word * ICWORDLEN);
end;
@ -436,12 +434,12 @@ begin
begin
do_read <= not stall_in;
do_write <= '0';
if r.recv_valid = '1' and r.store_way = i then
if r.recv_valid = '1' and r.store_way = to_unsigned(i, WAY_BITS) then
do_write <= '1';
end if;
cache_out(i) <= dout;
rd_addr <= std_ulogic_vector(to_unsigned(req_row, ROW_BITS));
wr_addr <= std_ulogic_vector(to_unsigned(r.store_row, ROW_BITS));
rd_addr <= std_ulogic_vector(req_row);
wr_addr <= std_ulogic_vector(r.store_row);
wr_sel(0) <= do_write;
end process;
end generate;
@ -478,7 +476,7 @@ begin
else
plru_acc_en <= '0';
end if;
plru_acc <= std_ulogic_vector(to_unsigned(r.hit_way, WAY_BITS));
plru_acc <= std_ulogic_vector(r.hit_way);
plru_victim(i) <= plru_out;
end process;
end generate;
@ -550,15 +548,13 @@ begin
-- Cache hit detection, output to fetch2 and other misc logic
icache_comb : process(all)
variable is_hit : std_ulogic;
variable hit_way : way_t;
variable hit_way : way_sig_t;
variable insn : std_ulogic_vector(ICWORDLEN - 1 downto 0);
variable icode : insn_code;
begin
-- Extract line, row and tag from request
if not is_X(i_in.nia) then
req_index <= get_index(i_in.nia);
req_row <= get_row(i_in.nia);
end if;
req_index <= get_index(i_in.nia);
req_row <= get_row(i_in.nia);
req_tag <= get_tag(real_addr, i_in.big_endian);

-- Calculate address of beginning of cache row, will be
@ -568,21 +564,20 @@ begin
(ROW_OFF_BITS-1 downto 0 => '0');

-- Test if pending request is a hit on any way
hit_way := 0;
hit_way := to_unsigned(0, WAY_BITS);
is_hit := '0';
if i_in.req = '1' then
assert not is_X(req_index) and not is_X(req_row) severity failure;
end if;
for i in way_t loop
if is_X(i_in.nia) then
-- FIXME: This is fragile
-- req_index or req_row could be a metavalue
is_hit := 'X';
elsif i_in.req = '1' and
(cache_valids(req_index)(i) = '1' or
if i_in.req = '1' and
(cache_valids(to_integer(req_index))(i) = '1' or
(r.state = WAIT_ACK and
req_index = r.store_index and
i = r.store_way and
r.rows_valid(req_row mod ROW_PER_LINE) = '1')) then
if read_tag(i, cache_tags(req_index)) = req_tag then
hit_way := i;
to_unsigned(i, WAY_BITS) = r.store_way and
r.rows_valid(to_integer(req_row(ROW_LINEBITS-1 downto 0))) = '1')) then
if read_tag(i, cache_tags(to_integer(req_index))) = req_tag then
hit_way := to_unsigned(i, WAY_BITS);
is_hit := '1';
end if;
end if;
@ -598,13 +593,6 @@ begin
end if;
req_hit_way <= hit_way;

-- The way to replace on a miss
if r.state = CLR_TAG then
replace_way <= to_integer(unsigned(plru_victim(r.store_index)));
else
replace_way <= r.store_way;
end if;

-- Output instruction from current cache row
--
-- Note: This is a mild violation of our design principle of having pipeline
@ -616,10 +604,13 @@ begin
insn := (others => '0');
icode := INSN_illegal;
if r.hit_valid = '1' then
insn := read_insn_word(r.hit_nia, cache_out(r.hit_way));
assert not is_X(r.hit_way) severity failure;
insn := read_insn_word(r.hit_nia, cache_out(to_integer(r.hit_way)));
-- Currently we use only the top bit for indicating illegal
-- instructions because we know that insn_codes fit into 9 bits.
if insn(ICWORDLEN - 1) = '0' then
if is_X(insn) then
insn := (others => '0');
elsif insn(ICWORDLEN - 1) = '0' then
icode := insn_code'val(to_integer(unsigned(insn(ICWORDLEN-1 downto INSN_IMAGE_BITS))));
end if;
end if;
@ -664,9 +655,9 @@ begin
report "cache hit nia:" & to_hstring(i_in.nia) &
" IR:" & std_ulogic'image(i_in.virt_mode) &
" SM:" & std_ulogic'image(i_in.stop_mark) &
" idx:" & integer'image(req_index) &
" idx:" & to_hstring(req_index) &
" tag:" & to_hstring(req_tag) &
" way:" & integer'image(req_hit_way) &
" way:" & to_hstring(req_hit_way) &
" RA:" & to_hstring(real_addr);
end if;
end if;
@ -676,6 +667,9 @@ begin
r.hit_nia <= i_in.nia;
r.big_endian <= i_in.big_endian;
end if;
if i_out.valid = '1' then
assert not is_X(i_out.insn) severity failure;
end if;
end if;
end process;

@ -686,7 +680,7 @@ begin
variable snoop_addr : real_addr_t;
variable snoop_tag : cache_tag_t;
variable snoop_cache_tags : cache_tags_set_t;
variable replace_way : way_t;
variable replace_way : way_sig_t;
begin
if rising_edge(clk) then
ev.icache_miss <= '0';
@ -709,7 +703,7 @@ begin
r.wb.adr <= (others => '0');

snoop_valid <= '0';
snoop_index <= 0;
snoop_index <= to_unsigned(0, INDEX_BITS);
snoop_hits <= (others => '0');
else
-- Detect snooped writes and decode address into index and tag
@ -717,20 +711,22 @@ begin
snoop_valid <= wb_snoop_in.cyc and wb_snoop_in.stb and wb_snoop_in.we;
snoop_addr := addr_to_real(wb_to_addr(wb_snoop_in.adr));
snoop_index <= get_index(snoop_addr);
snoop_cache_tags := cache_tags(get_index(snoop_addr));
if snoop_valid = '1' and is_X(snoop_addr) then
report "metavalue in snoop_addr" severity FAILURE;
end if;
snoop_tag := get_tag(snoop_addr, '0');
snoop_hits <= (others => '0');
for i in way_t loop
tag := read_tag(i, snoop_cache_tags);
-- Ignore endian bit in comparison
tag(TAG_BITS - 1) := '0';
if tag = snoop_tag then
snoop_hits(i) <= '1';
if snoop_valid = '1' then
if is_X(snoop_addr) then
report "metavalue in snoop_addr" severity FAILURE;
end if;
end loop;
snoop_cache_tags := cache_tags(to_integer(get_index(snoop_addr)));
for i in way_t loop
tag := read_tag(i, snoop_cache_tags);
-- Ignore endian bit in comparison
tag(TAG_BITS - 1) := '0';
if tag = snoop_tag then
snoop_hits(i) <= '1';
end if;
end loop;
end if;

-- Process cache invalidations
if inval_in = '1' then
@ -742,8 +738,9 @@ begin
-- Do invalidations from snooped stores to memory, one
-- cycle after the address appears on wb_snoop_in.
for i in way_t loop
if snoop_valid = '1' and snoop_hits(i) = '1' then
cache_valids(snoop_index)(i) <= '0';
if snoop_hits(i) = '1' then
assert not is_X(snoop_index) severity failure;
cache_valids(to_integer(snoop_index))(i) <= '0';
end if;
end loop;
end if;
@ -761,7 +758,7 @@ begin
report "cache miss nia:" & to_hstring(i_in.nia) &
" IR:" & std_ulogic'image(i_in.virt_mode) &
" SM:" & std_ulogic'image(i_in.stop_mark) &
" idx:" & integer'image(req_index) &
" idx:" & to_hstring(req_index) &
" tag:" & to_hstring(req_tag) &
" RA:" & to_hstring(real_addr);
ev.icache_miss <= '1';
@ -786,20 +783,24 @@ begin
end if;

when CLR_TAG | WAIT_ACK =>
assert not is_X(r.store_index) severity failure;
assert not is_X(r.store_row) severity failure;
assert not is_X(r.recv_row) severity failure;
if r.state = CLR_TAG then
-- Get victim way from plru
replace_way := to_integer(unsigned(plru_victim(r.store_index)));
replace_way := unsigned(plru_victim(to_integer(r.store_index)));
r.store_way <= replace_way;

-- Force misses on that way while reloading that line
cache_valids(req_index)(replace_way) <= '0';
assert not is_X(replace_way) severity failure;
cache_valids(to_integer(r.store_index))(to_integer(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(r.store_index);
if to_unsigned(i, WAY_BITS) = replace_way then
tagset := cache_tags(to_integer(r.store_index));
write_tag(i, tagset, r.store_tag);
cache_tags(r.store_index) <= tagset;
cache_tags(to_integer(r.store_index)) <= tagset;
end if;
end loop;

@ -808,10 +809,11 @@ begin

-- If we are writing in this cycle, mark row valid and see if we are done
if r.recv_valid = '1' then
r.rows_valid(r.store_row mod ROW_PER_LINE) <= not inval_in;
r.rows_valid(to_integer(r.store_row(ROW_LINEBITS-1 downto 0))) <= not inval_in;
if is_last_row(r.store_row, r.end_row_ix) then
-- Cache line is now valid
cache_valids(r.store_index)(r.store_way) <= r.store_valid and not inval_in;
cache_valids(to_integer(r.store_index))(to_integer(r.store_way)) <=
r.store_valid and not inval_in;
-- We are done
r.state <= IDLE;
end if;
@ -878,7 +880,7 @@ begin
signal log_data : std_ulogic_vector(57 downto 0);
begin
data_log: process(clk)
variable lway: way_t;
variable lway: way_sig_t;
variable wstate: std_ulogic;
begin
if rising_edge(clk) then
@ -897,7 +899,7 @@ begin
r.fetch_failed &
r.hit_nia(5 downto 2) &
wstate &
std_ulogic_vector(to_unsigned(lway, 3)) &
std_ulogic_vector(resize(lway, 3)) &
req_is_hit & req_is_miss &
access_ok &
ra_valid;

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