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Simplify flow control in the dcache and loadstore units

Browse Source 
Simplify the flow control by stalling the whole upstream pipeline when
a stage can't proceed, instead of trying to let each stage progress
independently when it can.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/379/head
Paul Mackerras 2 years ago
parent 35e0dbed34
commit bdd4d04162
2 changed files with 173 additions and 167 deletions
Show Stats Download Patch File Download Diff File

6
dcache.vhdl
Unescape Escape View File

@ -588,7 +588,7 @@ begin
end if;
if rst = '1' then
r0_full <= '0';
elsif (r1.full = '0' and d_in.hold = '0') or r0_full = '0' then
elsif r1.full = '0' and d_in.hold = '0' then
r0 <= r;
r0_full <= r.req.valid;
elsif r0.d_valid = '0' then
@ -605,9 +605,9 @@ begin
m_out.stall <= '0';

-- Hold off the request in r0 when r1 has an uncompleted request
r0_stall <= r0_full and (r1.full or d_in.hold);
r0_stall <= r1.full or d_in.hold;
r0_valid <= r0_full and not r1.full and not d_in.hold;
stall_out <= r0_stall;
stall_out <= r1.full;

events <= ev;


334
loadstore1.vhdl
Unescape Escape View File

@ -43,9 +43,7 @@ architecture behave of loadstore1 is

-- State machine for unaligned loads/stores
type state_t is (IDLE, -- ready for instruction
MMU_LOOKUP, -- waiting for MMU to look up translation
TLBIE_WAIT, -- waiting for MMU to finish doing a tlbie
FINISH_LFS -- write back converted SP data for lfs*
MMU_WAIT -- waiting for MMU to finish doing something
);

type byte_index_t is array(0 to 7) of unsigned(2 downto 0);
@ -63,9 +61,7 @@ architecture behave of loadstore1 is
write_spr : std_ulogic;
mmu_op : std_ulogic;
instr_fault : std_ulogic;
load_zero : std_ulogic;
do_update : std_ulogic;
noop : std_ulogic;
mode_32bit : std_ulogic;
addr : std_ulogic_vector(63 downto 0);
byte_sel : std_ulogic_vector(7 downto 0);
@ -93,11 +89,12 @@ architecture behave of loadstore1 is
align_intr : std_ulogic;
dword_index : std_ulogic;
two_dwords : std_ulogic;
incomplete : std_ulogic;
nia : std_ulogic_vector(63 downto 0);
end record;
constant request_init : request_t := (valid => '0', dc_req => '0', load => '0', store => '0', tlbie => '0',
dcbz => '0', read_spr => '0', write_spr => '0', mmu_op => '0',
instr_fault => '0', load_zero => '0', do_update => '0', noop => '0',
instr_fault => '0', do_update => '0',
mode_32bit => '0', addr => (others => '0'),
byte_sel => x"00", second_bytes => x"00",
store_data => (others => '0'), instr_tag => instr_tag_init,
@ -108,11 +105,12 @@ architecture behave of loadstore1 is
atomic => '0', atomic_last => '0', rc => '0', nc => '0',
virt_mode => '0', priv_mode => '0', load_sp => '0',
sprn => 10x"0", is_slbia => '0', align_intr => '0',
dword_index => '0', two_dwords => '0',
dword_index => '0', two_dwords => '0', incomplete => '0',
nia => (others => '0'));

type reg_stage1_t is record
req : request_t;
busy : std_ulogic;
issued : std_ulogic;
addr0 : std_ulogic_vector(63 downto 0);
end record;
@ -121,6 +119,7 @@ architecture behave of loadstore1 is
req : request_t;
byte_index : byte_index_t;
use_second : std_ulogic_vector(7 downto 0);
busy : std_ulogic;
wait_dc : std_ulogic;
wait_mmu : std_ulogic;
one_cycle : std_ulogic;
@ -130,6 +129,7 @@ architecture behave of loadstore1 is

type reg_stage3_t is record
state : state_t;
complete : std_ulogic;
instr_tag : instr_tag_t;
write_enable : std_ulogic;
write_reg : gspr_index_t;
@ -137,7 +137,6 @@ architecture behave of loadstore1 is
rc : std_ulogic;
xerc : xer_common_t;
store_done : std_ulogic;
convert_lfs : std_ulogic;
load_data : std_ulogic_vector(63 downto 0);
dar : std_ulogic_vector(63 downto 0);
dsisr : std_ulogic_vector(31 downto 0);
@ -157,6 +156,7 @@ architecture behave of loadstore1 is
signal r2, r2in : reg_stage2_t;
signal r3, r3in : reg_stage3_t;

signal flush : std_ulogic;
signal busy : std_ulogic;
signal complete : std_ulogic;
signal in_progress : std_ulogic;
@ -166,12 +166,9 @@ architecture behave of loadstore1 is
signal load_dp_data : std_ulogic_vector(63 downto 0);
signal store_data : std_ulogic_vector(63 downto 0);

signal stage1_issue_enable : std_ulogic;
signal stage1_req : request_t;
signal stage1_dcreq : std_ulogic;
signal stage1_dreq : std_ulogic;
signal stage2_busy_next : std_ulogic;
signal stage3_busy_next : std_ulogic;

-- Generate byte enables from sizes
function length_to_sel(length : in std_logic_vector(3 downto 0)) return std_ulogic_vector is
@ -274,7 +271,11 @@ begin
begin
if rising_edge(clk) then
if rst = '1' then
r1.busy <= '0';
r1.issued <= '0';
r1.req.valid <= '0';
r1.req.dc_req <= '0';
r1.req.incomplete <= '0';
r1.req.tlbie <= '0';
r1.req.is_slbia <= '0';
r1.req.instr_fault <= '0';
@ -284,6 +285,7 @@ begin
r1.req.xerc <= xerc_init;

r2.req.valid <= '0';
r2.busy <= '0';
r2.req.tlbie <= '0';
r2.req.is_slbia <= '0';
r2.req.instr_fault <= '0';
@ -301,8 +303,8 @@ begin
r3.state <= IDLE;
r3.write_enable <= '0';
r3.interrupt <= '0';
r3.complete <= '0';
r3.stage1_en <= '1';
r3.convert_lfs <= '0';
r3.events.load_complete <= '0';
r3.events.store_complete <= '0';
flushing <= '0';
@ -311,7 +313,7 @@ begin
r2 <= r2in;
r3 <= r3in;
flushing <= (flushing or (r1in.req.valid and r1in.req.align_intr)) and
not r3in.interrupt;
not flush;
end if;
stage1_dreq <= stage1_dcreq;
if d_in.valid = '1' then
@ -321,7 +323,7 @@ begin
assert r2.req.valid = '1' and r2.req.dc_req = '1' and r3.state = IDLE severity failure;
end if;
if m_in.done = '1' or m_in.err = '1' then
assert r2.req.valid = '1' and (r3.state = MMU_LOOKUP or r3.state = TLBIE_WAIT) severity failure;
assert r2.req.valid = '1' and r3.state = MMU_WAIT severity failure;
end if;
end if;
end process;
@ -507,6 +509,7 @@ begin
when others =>
end case;
v.dc_req := l_in.valid and (v.load or v.store or v.dcbz) and not v.align_intr;
v.incomplete := v.dc_req and v.two_dwords;

-- Work out controls for load and store formatting
brev_lenm1 := "000";
@ -518,17 +521,10 @@ begin
req_in <= v;
end process;

busy <= r1.req.valid and ((r1.req.dc_req and not r1.issued) or
(r1.issued and d_in.error) or
stage2_busy_next or
(r1.req.dc_req and r1.req.two_dwords and not r1.req.dword_index));
complete <= r2.one_cycle or (r2.wait_dc and d_in.valid) or
(r2.wait_mmu and m_in.done) or r3.convert_lfs;
busy <= dc_stall or d_in.error or r1.busy or r2.busy;
complete <= r2.one_cycle or (r2.wait_dc and d_in.valid) or r3.complete;
in_progress <= r1.req.valid or (r2.req.valid and not complete);

stage1_issue_enable <= r3.stage1_en and not (r1.req.valid and r1.req.mmu_op) and
not (r2.req.valid and r2.req.mmu_op);

-- Processing done in the first cycle of a load/store instruction
loadstore1_1: process(all)
variable v : reg_stage1_t;
@ -538,10 +534,11 @@ begin
begin
v := r1;
issue := '0';
dcreq := '0';

if busy = '0' then
if r1.busy = '0' then
req := req_in;
v.issued := '0';
req.valid := l_in.valid;
if flushing = '1' then
-- Make this a no-op request rather than simply invalid.
-- It will never get to stage 3 since there is a request ahead of
@ -554,37 +551,49 @@ begin
end if;
else
req := r1.req;
end if;

if r1.req.valid = '1' then
if r1.req.dc_req = '1' and r1.issued = '0' then
issue := '1';
elsif r1.issued = '1' and d_in.error = '1' then
v.issued := '0';
elsif stage2_busy_next = '0' then
-- we can change what's in r1 next cycle because the current thing
-- in r1 will go into r2
if r1.req.dc_req = '1' and r1.req.two_dwords = '1' and r1.req.dword_index = '0' then
-- construct the second request for a misaligned access
req.dword_index := '1';
req.addr := std_ulogic_vector(unsigned(r1.req.addr(63 downto 3)) + 1) & "000";
if r1.req.mode_32bit = '1' then
req.addr(32) := '0';
end if;
req.byte_sel := r1.req.second_bytes;
issue := '1';
elsif r1.req.incomplete = '1' then
-- construct the second request for a misaligned access
req.dword_index := '1';
req.incomplete := '0';
req.addr := std_ulogic_vector(unsigned(r1.req.addr(63 downto 3)) + 1) & "000";
if r1.req.mode_32bit = '1' then
req.addr(32) := '0';
end if;
req.byte_sel := r1.req.second_bytes;
issue := '1';
else
-- For the lfs conversion cycle, leave the request valid
-- for another cycle but with req.dc_req = 0.
-- For an MMU request last cycle, we have nothing
-- to do in this cycle, so make it invalid.
if r1.req.load_sp = '0' then
req.valid := '0';
end if;
req.dc_req := '0';
end if;
end if;
if r3in.interrupt = '1' then
req.valid := '0';
issue := '0';
end if;

v.req := req;
dcreq := issue and stage1_issue_enable and not d_in.error and not dc_stall;
if issue = '1' then
v.issued := dcreq;
if flush = '1' then
v.req.valid := '0';
v.req.dc_req := '0';
v.req.incomplete := '0';
v.issued := '0';
v.busy := '0';
elsif (dc_stall or d_in.error or r2.busy) = '0' then
-- we can change what's in r1 next cycle because the current thing
-- in r1 will go into r2
v.req := req;
dcreq := issue;
v.issued := issue;
v.busy := (issue and (req.incomplete or req.load_sp)) or (req.valid and req.mmu_op);
else
-- pipeline is stalled
if r1.issued = '1' and d_in.error = '1' then
v.issued := '0';
v.busy := '1';
end if;
end if;

stage1_req <= req;
@ -602,6 +611,7 @@ begin
variable kk : unsigned(3 downto 0);
variable idx : unsigned(2 downto 0);
variable byte_offset : unsigned(2 downto 0);
variable interrupt : std_ulogic;
begin
v := r2;

@ -614,44 +624,61 @@ begin
store_data(i * 8 + 7 downto i * 8) <= r1.req.store_data(j + 7 downto j);
end loop;

if stage3_busy_next = '0' and
(r1.req.valid = '0' or r1.issued = '1' or r1.req.dc_req = '0') then
v.req := r1.req;
v.addr0 := r1.addr0;
v.req.store_data := store_data;
v.wait_dc := r1.req.valid and r1.req.dc_req and not r1.req.load_sp and
not (r1.req.two_dwords and not r1.req.dword_index);
v.wait_mmu := r1.req.valid and r1.req.mmu_op;
v.one_cycle := r1.req.valid and (r1.req.noop or r1.req.read_spr or
(r1.req.write_spr and not r1.req.mmu_op) or
r1.req.load_zero or r1.req.do_update);
if r1.req.read_spr = '1' then
v.wr_sel := "00";
elsif r1.req.do_update = '1' or r1.req.store = '1' then
v.wr_sel := "01";
elsif r1.req.load_sp = '1' then
v.wr_sel := "10";
if (dc_stall or d_in.error or r2.busy) = '0' then
if r1.req.valid = '0' or r1.issued = '1' or r1.req.dc_req = '0' then
v.req := r1.req;
v.addr0 := r1.addr0;
v.req.store_data := store_data;
v.wait_dc := r1.req.valid and r1.req.dc_req and not r1.req.load_sp and
not r1.req.incomplete;
v.wait_mmu := r1.req.valid and r1.req.mmu_op;
v.busy := r1.req.valid and r1.req.mmu_op;
v.one_cycle := r1.req.valid and not (r1.req.dc_req or r1.req.mmu_op);
if r1.req.read_spr = '1' then
v.wr_sel := "00";
elsif r1.req.do_update = '1' or r1.req.store = '1' then
v.wr_sel := "01";
elsif r1.req.load_sp = '1' then
v.wr_sel := "10";
else
v.wr_sel := "11";
end if;

-- Work out load formatter controls for next cycle
for i in 0 to 7 loop
idx := to_unsigned(i, 3) xor r1.req.brev_mask;
kk := ('0' & idx) + ('0' & byte_offset);
v.use_second(i) := kk(3);
v.byte_index(i) := kk(2 downto 0);
end loop;
else
v.wr_sel := "11";
v.req.valid := '0';
v.wait_dc := '0';
v.wait_mmu := '0';
v.one_cycle := '0';
end if;
end if;
if r2.wait_mmu = '1' and m_in.done = '1' then
if r2.req.mmu_op = '1' then
v.req.valid := '0';
v.busy := '0';
end if;

-- Work out load formatter controls for next cycle
for i in 0 to 7 loop
idx := to_unsigned(i, 3) xor r1.req.brev_mask;
kk := ('0' & idx) + ('0' & byte_offset);
v.use_second(i) := kk(3);
v.byte_index(i) := kk(2 downto 0);
end loop;
elsif stage3_busy_next = '0' then
v.req.valid := '0';
v.wait_dc := '0';
v.wait_mmu := '0';
end if;
if r2.busy = '1' and r2.wait_mmu = '0' then
v.busy := '0';
end if;

stage2_busy_next <= r1.req.valid and stage3_busy_next;

if r3in.interrupt = '1' then
interrupt := (r2.req.valid and r2.req.align_intr) or
(d_in.error and d_in.cache_paradox) or m_in.err;
if interrupt = '1' then
v.req.valid := '0';
v.busy := '0';
v.wait_dc := '0';
v.wait_mmu := '0';
elsif d_in.error = '1' then
v.wait_mmu := '1';
v.busy := '1';
end if;

r2in <= v;
@ -671,7 +698,6 @@ begin
variable write_data : std_ulogic_vector(63 downto 0);
variable do_update : std_ulogic;
variable done : std_ulogic;
variable part_done : std_ulogic;
variable exception : std_ulogic;
variable data_permuted : std_ulogic_vector(63 downto 0);
variable data_trimmed : std_ulogic_vector(63 downto 0);
@ -687,13 +713,12 @@ begin
mmureq := '0';
mmu_mtspr := '0';
done := '0';
part_done := '0';
exception := '0';
dsisr := (others => '0');
write_enable := '0';
sprval := (others => '0');
do_update := '0';
v.convert_lfs := '0';
v.complete := '0';
v.srr1 := (others => '0');
v.events := (others => '0');

@ -775,94 +800,74 @@ begin
-- generate alignment interrupt
exception := '1';
end if;
if r2.req.load_zero = '1' then
write_enable := '1';
end if;
if r2.req.do_update = '1' then
do_update := '1';
end if;
end if;

case r3.state is
when IDLE =>
if d_in.valid = '1' then
if r2.req.two_dwords = '0' or r2.req.dword_index = '1' then
write_enable := r2.req.load and not r2.req.load_sp;
if HAS_FPU and r2.req.load_sp = '1' then
-- SP to DP conversion takes a cycle
v.state := FINISH_LFS;
v.convert_lfs := '1';
else
-- stores write back rA update
do_update := r2.req.update and r2.req.store;
end if;
else
part_done := '1';
end if;
if r2.req.load_sp = '1' and r2.req.dc_req = '0' then
write_enable := '1';
end if;
if d_in.error = '1' then
if d_in.cache_paradox = '1' then
-- signal an interrupt straight away
exception := '1';
dsisr(63 - 38) := not r2.req.load;
-- XXX there is no architected bit for this
-- (probably should be a machine check in fact)
dsisr(63 - 35) := d_in.cache_paradox;
if r2.req.write_spr = '1' and r2.req.mmu_op = '0' then
if r2.req.sprn(0) = '0' then
v.dsisr := r2.req.store_data(31 downto 0);
else
-- Look up the translation for TLB miss
-- and also for permission error and RC error
-- in case the PTE has been updated.
mmureq := '1';
v.state := MMU_LOOKUP;
v.stage1_en := '0';
v.dar := r2.req.store_data;
end if;
end if;
if r2.req.valid = '1' then
if r2.req.mmu_op = '1' then
-- send request (tlbie, mtspr, itlb miss) to MMU
mmureq := not r2.req.write_spr;
mmu_mtspr := r2.req.write_spr;
if r2.req.instr_fault = '1' then
v.state := MMU_LOOKUP;
v.events.itlb_miss := '1';
else
v.state := TLBIE_WAIT;
end if;
elsif r2.req.write_spr = '1' then
if r2.req.sprn(0) = '0' then
v.dsisr := r2.req.store_data(31 downto 0);
else
v.dar := r2.req.store_data;
end if;
end if;
end if;

if r3.state = IDLE and r2.req.valid = '1' and r2.req.mmu_op = '1' then
-- send request (tlbie, mtspr, itlb miss) to MMU
mmureq := not r2.req.write_spr;
mmu_mtspr := r2.req.write_spr;
if r2.req.instr_fault = '1' then
v.events.itlb_miss := '1';
end if;
v.state := MMU_WAIT;
end if;

when MMU_LOOKUP =>
if m_in.done = '1' then
if r2.req.instr_fault = '0' then
-- retry the request now that the MMU has installed a TLB entry
req := '1';
v.stage1_en := '1';
v.state := IDLE;
end if;
if d_in.valid = '1' then
if r2.req.incomplete = '0' then
write_enable := r2.req.load and not r2.req.load_sp;
-- stores write back rA update
do_update := r2.req.update and r2.req.store;
end if;
if m_in.err = '1' then
end if;
if d_in.error = '1' then
if d_in.cache_paradox = '1' then
-- signal an interrupt straight away
exception := '1';
dsisr(63 - 33) := m_in.invalid;
dsisr(63 - 36) := m_in.perm_error;
dsisr(63 - 38) := r2.req.store or r2.req.dcbz;
dsisr(63 - 44) := m_in.badtree;
dsisr(63 - 45) := m_in.rc_error;
dsisr(63 - 38) := not r2.req.load;
-- XXX there is no architected bit for this
-- (probably should be a machine check in fact)
dsisr(63 - 35) := d_in.cache_paradox;
else
-- Look up the translation for TLB miss
-- and also for permission error and RC error
-- in case the PTE has been updated.
mmureq := '1';
v.state := MMU_WAIT;
v.stage1_en := '0';
end if;
end if;

when TLBIE_WAIT =>

when FINISH_LFS =>
write_enable := '1';

end case;
if m_in.done = '1' then
if r2.req.dc_req = '1' then
-- retry the request now that the MMU has installed a TLB entry
req := '1';
else
v.complete := '1';
end if;
end if;
if m_in.err = '1' then
exception := '1';
dsisr(63 - 33) := m_in.invalid;
dsisr(63 - 36) := m_in.perm_error;
dsisr(63 - 38) := r2.req.store or r2.req.dcbz;
dsisr(63 - 44) := m_in.badtree;
dsisr(63 - 45) := m_in.rc_error;
end if;

if complete = '1' or exception = '1' then
if (m_in.done or m_in.err) = '1' then
v.stage1_en := '1';
v.state := IDLE;
end if;
@ -915,7 +920,7 @@ begin
end case;

-- Update outputs to dcache
if stage1_issue_enable = '1' then
if r3.stage1_en = '1' then
d_out.valid <= stage1_dcreq;
d_out.load <= stage1_req.load;
d_out.dcbz <= stage1_req.dcbz;
@ -945,7 +950,7 @@ begin
else
d_out.data <= r2.req.store_data;
end if;
d_out.hold <= r2.req.valid and r2.req.load_sp and d_in.valid;
d_out.hold <= '0';

-- Update outputs to MMU
m_out.valid <= mmureq;
@ -980,8 +985,7 @@ begin

events <= r3.events;

-- Busy calculation.
stage3_busy_next <= r2.req.valid and not (complete or part_done or exception);
flush <= exception;

-- Update registers
r3in <= v;
@ -1001,7 +1005,9 @@ begin
d_out.valid &
m_in.done &
r2.req.dword_index &
std_ulogic_vector(to_unsigned(state_t'pos(r3.state), 3));
r2.req.valid &
r2.wait_dc &
std_ulogic_vector(to_unsigned(state_t'pos(r3.state), 1));
end if;
end process;
log_out <= log_data;

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