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loadstore1: Do SPR reading in stage 2 rather than stage 3

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This eliminates one leg of the output value multiplexer, and seems
to improve timing slightly on the A7-100.

Since SPR values are written in stage 3 and read in stage 2, an mfspr
immediately following an mtspr to the same SPR won't give the correct
value.  To avoid this, we make mtspr to the load/store SPRs single
issue in decode1.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/379/head
Paul Mackerras 2 years ago
parent af814a0d5e
commit 047be5c0c3
2 changed files with 62 additions and 56 deletions
Show Stats Download Patch File Download Diff File

4
decode1.vhdl
Unescape Escape View File

@ -681,6 +681,10 @@ begin
when SPR_DAR | SPR_DSISR | SPR_PID | SPR_PTCR =>
vi.override_decode.unit := LDST;
vi.override_unit := '1';
-- make mtspr to loadstore SPRs single-issue
if f_in.insn(8) = '1' then
vi.force_single := '1';
end if;
when others =>
end case;
end if;

114
loadstore1.vhdl
Unescape Escape View File

@ -90,7 +90,8 @@ architecture behave of loadstore1 is
virt_mode : std_ulogic;
priv_mode : std_ulogic;
load_sp : std_ulogic;
sprn : std_ulogic_vector(9 downto 0);
sprsel : std_ulogic_vector(1 downto 0);
ric : std_ulogic_vector(1 downto 0);
is_slbia : std_ulogic;
align_intr : std_ulogic;
dword_index : std_ulogic;
@ -109,7 +110,7 @@ architecture behave of loadstore1 is
xerc => xerc_init, reserve => '0',
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',
sprsel => "00", ric => "00", is_slbia => '0', align_intr => '0',
dword_index => '0', two_dwords => '0', incomplete => '0');

type reg_stage1_t is record
@ -130,7 +131,8 @@ architecture behave of loadstore1 is
wr_sel : std_ulogic_vector(1 downto 0);
addr0 : std_ulogic_vector(63 downto 0);
sprsel : std_ulogic_vector(1 downto 0);
dbg_spr_rd : std_ulogic;
dbg_spr : std_ulogic_vector(63 downto 0);
dbg_spr_ack: std_ulogic;
end record;

type reg_stage3_t is record
@ -154,8 +156,6 @@ architecture behave of loadstore1 is
intr_vec : integer range 0 to 16#fff#;
srr1 : std_ulogic_vector(15 downto 0);
events : Loadstore1EventType;
dbg_spr : std_ulogic_vector(63 downto 0);
dbg_spr_ack : std_ulogic;
end record;

signal req_in : request_t;
@ -287,7 +287,8 @@ begin
r1.req.instr_fault <= '0';
r1.req.load <= '0';
r1.req.priv_mode <= '0';
r1.req.sprn <= (others => '0');
r1.req.sprsel <= "00";
r1.req.ric <= "00";
r1.req.xerc <= xerc_init;

r2.req.valid <= '0';
@ -297,7 +298,8 @@ begin
r2.req.instr_fault <= '0';
r2.req.load <= '0';
r2.req.priv_mode <= '0';
r2.req.sprn <= (others => '0');
r2.req.sprsel <= "00";
r2.req.ric <= "00";
r2.req.xerc <= xerc_init;

r2.wait_dc <= '0';
@ -418,7 +420,14 @@ begin
v.nc := l_in.ci;
v.virt_mode := l_in.virt_mode;
v.priv_mode := l_in.priv_mode;
v.sprn := sprn;
v.ric := l_in.insn(19 downto 18);
if sprn(1) = '1' then
-- DSISR and DAR
v.sprsel := '1' & sprn(0);
else
-- PID and PTCR
v.sprsel := '0' & sprn(8);
end if;

lsu_sum := std_ulogic_vector(unsigned(l_in.addr1) + unsigned(l_in.addr2));

@ -494,7 +503,7 @@ begin
v.read_spr := '1';
when OP_MTSPR =>
v.write_spr := '1';
v.mmu_op := sprn(8) or sprn(5);
v.mmu_op := not sprn(1);
when OP_FETCH_FAILED =>
-- send it to the MMU to do the radix walk
v.instr_fault := '1';
@ -605,6 +614,9 @@ begin
variable idx : unsigned(2 downto 0);
variable byte_offset : unsigned(2 downto 0);
variable interrupt : std_ulogic;
variable dbg_spr_rd : std_ulogic;
variable sprsel : std_ulogic_vector(1 downto 0);
variable sprval : std_ulogic_vector(63 downto 0);
begin
v := r2;

@ -617,6 +629,28 @@ begin
store_data(i * 8 + 7 downto i * 8) <= r1.req.store_data(j + 7 downto j);
end loop;

dbg_spr_rd := dbg_spr_req and not (r1.req.valid and r1.req.read_spr);
if dbg_spr_rd = '0' then
sprsel := r1.req.sprsel;
else
sprsel := dbg_spr_addr;
end if;
if sprsel(1) = '1' then
if sprsel(0) = '0' then
sprval := x"00000000" & r3.dsisr;
else
sprval := r3.dar;
end if;
else
sprval := m_in.sprval;
end if;
if dbg_spr_req = '0' then
v.dbg_spr_ack := '0';
elsif dbg_spr_rd = '1' and r2.dbg_spr_ack = '0' then
v.dbg_spr := sprval;
v.dbg_spr_ack := '1';
end if;

if (dc_stall or d_in.error or r2.busy or l_in.e2stall) = '0' then
if r1.req.valid = '0' or r1.issued = '1' or r1.req.dc_req = '0' then
v.req := r1.req;
@ -627,14 +661,15 @@ begin
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
if r1.req.do_update = '1' or r1.req.store = '1' or 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";
v.wr_sel := "01";
else
v.wr_sel := "11";
v.wr_sel := "10";
end if;
if r1.req.read_spr = '1' then
v.addr0 := sprval;
end if;

-- Work out load formatter controls for next cycle
@ -674,21 +709,11 @@ begin
v.busy := '1';
end if;

v.dbg_spr_rd := dbg_spr_req and not (v.req.valid and v.req.read_spr);
if v.dbg_spr_rd = '0' then
v.sprsel(1) := v.req.sprn(1);
if v.req.sprn(1) = '1' then
-- DSISR and DAR
v.sprsel(0) := v.req.sprn(0);
else
-- PID and PTCR
v.sprsel(0) := v.req.sprn(8);
end if;
else
v.sprsel := dbg_spr_addr;
end if;

r2in <= v;

-- SPR values for core_debug
dbg_spr_data <= r2.dbg_spr;
dbg_spr_ack <= r2.dbg_spr_ack;
end process;

-- Processing done in the third cycle of a load/store instruction.
@ -787,22 +812,6 @@ begin
v.load_data := data_permuted;
end if;

-- SPR mux
if r2.sprsel(1) = '1' then
if r2.sprsel(0) = '0' then
sprval := x"00000000" & r3.dsisr;
else
sprval := r3.dar;
end if;
else
sprval := m_in.sprval;
end if;
if dbg_spr_req = '0' then
v.dbg_spr_ack := '0';
elsif r2.dbg_spr_rd = '1' and r3.dbg_spr_ack = '0' then
v.dbg_spr := sprval;
v.dbg_spr_ack := '1';
end if;

if r2.req.valid = '1' then
if r2.req.read_spr = '1' then
@ -819,7 +828,7 @@ begin
write_enable := '1';
end if;
if r2.req.write_spr = '1' and r2.req.mmu_op = '0' then
if r2.req.sprn(0) = '0' then
if r2.req.sprsel(0) = '0' then
v.dsisr := r2.req.store_data(31 downto 0);
else
v.dar := r2.req.store_data;
@ -917,12 +926,9 @@ begin

case r2.wr_sel is
when "00" =>
-- mfspr result
write_data := sprval;
when "01" =>
-- update reg
write_data := r2.addr0;
when "10" =>
when "01" =>
-- lfs result
write_data := load_dp_data;
when others =>
@ -969,10 +975,10 @@ begin
m_out.load <= r2.req.load;
m_out.priv <= r2.req.priv_mode;
m_out.tlbie <= r2.req.tlbie;
m_out.ric <= r2.req.sprn(3 downto 2);
m_out.ric <= r2.req.ric;
m_out.mtspr <= mmu_mtspr;
m_out.sprnf <= r2.sprsel(0);
m_out.sprnt <= r2.req.sprn(8);
m_out.sprnf <= r1.req.sprsel(0);
m_out.sprnt <= r2.req.sprsel(0);
m_out.addr <= r2.req.addr;
m_out.slbia <= r2.req.is_slbia;
m_out.rs <= r2.req.store_data;
@ -998,10 +1004,6 @@ begin

flush <= exception;

-- SPR values for core_debug
dbg_spr_data <= r3.dbg_spr;
dbg_spr_ack <= r3.dbg_spr_ack;

-- Update registers
r3in <= v;


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