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loadstore2: Do data formatting after a register stage

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This moves the data formatting for read data to after a register,
instead of before, in order to improve timing.  The data formatting
is now effectively combinational logic on the input side of the
writeback stage.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/77/head
Paul Mackerras 5 years ago committed by Benjamin Herrenschmidt
parent 492bf06740
commit 9789d258fb
1 changed files with 49 additions and 36 deletions
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85
loadstore2.vhdl
Unescape Escape View File

@ -26,6 +26,10 @@ architecture behave of loadstore2 is
signal l_saved : Loadstore1ToLoadstore2Type;
signal w_tmp : Loadstore2ToWritebackType;
signal m_tmp : wishbone_master_out;
signal read_data : std_ulogic_vector(63 downto 0);
signal read_data_shift : std_ulogic_vector(2 downto 0);
signal sign_extend_byte_reverse: std_ulogic_vector(1 downto 0);
signal dlength : std_ulogic_vector(3 downto 0);

type state_t is (IDLE, WAITING_FOR_READ_ACK, WAITING_FOR_WRITE_ACK);
signal state : state_t := IDLE;
@ -56,21 +60,53 @@ architecture behave of loadstore2 is
return std_ulogic_vector(shift_left(unsigned(length_to_sel(size)), to_integer(unsigned(address(2 downto 0)))));
end function wishbone_data_sel;
begin

loadstore2_1: process(all)
variable tmp : std_ulogic_vector(63 downto 0);
variable data : std_ulogic_vector(63 downto 0);
begin
tmp := std_logic_vector(shift_right(unsigned(read_data), to_integer(unsigned(read_data_shift)) * 8));
data := (others => '0');
case to_integer(unsigned(dlength)) is
when 0 =>
when 1 =>
data(7 downto 0) := tmp(7 downto 0);
when 2 =>
data(15 downto 0) := tmp(15 downto 0);
when 4 =>
data(31 downto 0) := tmp(31 downto 0);
when 8 =>
data(63 downto 0) := tmp(63 downto 0);
when others =>
assert false report "invalid length" severity failure;
data(63 downto 0) := tmp(63 downto 0);
end case;

case sign_extend_byte_reverse is
when "10" =>
w_tmp.write_data <= sign_extend(data, to_integer(unsigned(l_saved.length)));
when "01" =>
w_tmp.write_data <= byte_reverse(data, to_integer(unsigned(l_saved.length)));
when others =>
w_tmp.write_data <= data;
end case;
end process;

w_out <= w_tmp;
m_out <= m_tmp;

loadstore2_0: process(clk)
variable tmp : std_ulogic_vector(63 downto 0);
variable data : std_ulogic_vector(63 downto 0);
variable sign_extend_byte_reverse : std_ulogic_vector(1 downto 0);
begin
if rising_edge(clk) then
tmp := (others => '0');
data := (others => '0');

w_tmp <= Loadstore2ToWritebackInit;
w_tmp.valid <= '0';
w_tmp.write_enable <= '0';
w_tmp.write_reg <= (others => '0');

l_saved <= l_saved;
read_data_shift <= "000";
sign_extend_byte_reverse <= "00";
dlength <= "1000";

case_0: case state is
when IDLE =>
@ -95,15 +131,14 @@ begin
if l_in.update = '1' then
w_tmp.write_enable <= '1';
w_tmp.write_reg <= l_in.update_reg;
w_tmp.write_data <= l_in.addr;
read_data <= l_in.addr;
end if;

state <= WAITING_FOR_READ_ACK;
else
m_tmp.we <= '1';

data := l_in.data;
m_tmp.dat <= std_logic_vector(shift_left(unsigned(data), wishbone_data_shift(l_in.addr)));
m_tmp.dat <= std_logic_vector(shift_left(unsigned(l_in.data), wishbone_data_shift(l_in.addr)));

assert l_in.sign_extend = '0' report "sign extension doesn't make sense for stores" severity failure;

@ -113,32 +148,10 @@ begin

when WAITING_FOR_READ_ACK =>
if m_in.ack = '1' then
tmp := std_logic_vector(shift_right(unsigned(m_in.dat), wishbone_data_shift(l_saved.addr)));
case to_integer(unsigned(l_saved.length)) is
when 0 =>
when 1 =>
data(7 downto 0) := tmp(7 downto 0);
when 2 =>
data(15 downto 0) := tmp(15 downto 0);
when 4 =>
data(31 downto 0) := tmp(31 downto 0);
when 8 =>
data(63 downto 0) := tmp(63 downto 0);
when others =>
assert false report "invalid length" severity failure;
end case;

sign_extend_byte_reverse := l_saved.sign_extend & l_saved.byte_reverse;

case sign_extend_byte_reverse is
when "10" =>
data := sign_extend(data, to_integer(unsigned(l_saved.length)));
when "01" =>
data := byte_reverse(data, to_integer(unsigned(l_saved.length)));
when others =>
end case;

w_tmp.write_data <= data;
read_data <= m_in.dat;
read_data_shift <= l_saved.addr(2 downto 0);
dlength <= l_saved.length;
sign_extend_byte_reverse <= l_saved.sign_extend & l_saved.byte_reverse;

-- write data to register file
w_tmp.valid <= '1';
@ -155,7 +168,7 @@ begin
if l_saved.update = '1' then
w_tmp.write_enable <= '1';
w_tmp.write_reg <= l_saved.update_reg;
w_tmp.write_data <= l_saved.addr;
read_data <= l_saved.addr;
end if;

m_tmp <= wishbone_master_out_init;

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