library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library work;
use work.common.all;
use work.crhelpers.all;
entity writeback is
port (
clk : in std_ulogic;
e_in : in Execute1ToWritebackType;
l_in : in DcacheToWritebackType;
m_in : in MultiplyToWritebackType;
d_in : in DividerToWritebackType;
w_out : out WritebackToRegisterFileType;
c_out : out WritebackToCrFileType;
complete_out : out std_ulogic
);
end entity writeback;
architecture behaviour of writeback is
subtype byte_index_t is unsigned(2 downto 0);
type permutation_t is array(0 to 7) of byte_index_t;
subtype byte_trim_t is std_ulogic_vector(1 downto 0);
type trim_ctl_t is array(0 to 7) of byte_trim_t;
type byte_sel_t is array(0 to 7) of std_ulogic;
signal data_len : unsigned(3 downto 0);
signal data_in : std_ulogic_vector(63 downto 0);
signal data_permuted : std_ulogic_vector(63 downto 0);
signal data_trimmed : std_ulogic_vector(63 downto 0);
signal data_latched : std_ulogic_vector(63 downto 0);
signal perm : permutation_t;
signal use_second : byte_sel_t;
signal byte_offset : unsigned(2 downto 0);
signal brev_lenm1 : unsigned(2 downto 0);
signal trim_ctl : trim_ctl_t;
signal rc : std_ulogic;
signal partial_write : std_ulogic;
signal sign_extend : std_ulogic;
signal negative : std_ulogic;
signal second_word : std_ulogic;
begin
writeback_0: process(clk)
begin
if rising_edge(clk) then
if partial_write = '1' then
data_latched <= data_permuted;
end if;
end if;
end process;
writeback_1: process(all)
variable x : std_ulogic_vector(0 downto 0);
variable y : std_ulogic_vector(0 downto 0);
variable z : std_ulogic_vector(0 downto 0);
variable w : std_ulogic_vector(0 downto 0);
variable j : integer;
variable k : unsigned(3 downto 0);
begin
x := "" & e_in.valid;
y := "" & l_in.valid;
z := "" & m_in.valid;
w := "" & d_in.valid;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) + to_integer(unsigned(z)) + to_integer(unsigned(w))) <= 1 severity failure;
x := "" & e_in.write_enable;
y := "" & l_in.write_enable;
z := "" & m_in.write_reg_enable;
w := "" & d_in.write_reg_enable;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) + to_integer(unsigned(z)) + to_integer(unsigned(w))) <= 1 severity failure;
w := "" & e_in.write_cr_enable;
x := "" & (e_in.write_enable and e_in.rc);
y := "" & (m_in.valid and m_in.rc);
z := "" & (d_in.valid and d_in.rc);
assert (to_integer(unsigned(w)) + to_integer(unsigned(x)) + to_integer(unsigned(y)) + to_integer(unsigned(z))) <= 1 severity failure;
w_out <= WritebackToRegisterFileInit;
c_out <= WritebackToCrFileInit;
complete_out <= '0';
if e_in.valid = '1' or l_in.valid = '1' or m_in.valid = '1' or d_in.valid = '1' then
complete_out <= '1';
end if;
rc <= '0';
brev_lenm1 <= "000";
byte_offset <= "000";
data_len <= x"8";
partial_write <= '0';
sign_extend <= '0';
second_word <= '0';
data_in <= e_in.write_data;
if e_in.write_enable = '1' then
w_out.write_reg <= e_in.write_reg;
data_in <= e_in.write_data;
w_out.write_enable <= '1';
data_len <= unsigned(e_in.write_len);
sign_extend <= e_in.sign_extend;
rc <= e_in.rc;
end if;
if e_in.write_cr_enable = '1' then
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= e_in.write_cr_mask;
c_out.write_cr_data <= e_in.write_cr_data;
end if;
if l_in.write_enable = '1' then
w_out.write_reg <= l_in.write_reg;
data_in <= l_in.write_data;
data_len <= unsigned(l_in.write_len);
byte_offset <= unsigned(l_in.write_shift);
sign_extend <= l_in.sign_extend;
if l_in.byte_reverse = '1' then
brev_lenm1 <= unsigned(l_in.write_len(2 downto 0)) - 1;
end if;
w_out.write_enable <= '1';
second_word <= l_in.second_word;
if l_in.valid = '0' and (data_len + byte_offset > 8) then
partial_write <= '1';
end if;
end if;
if m_in.write_reg_enable = '1' then
w_out.write_enable <= '1';
w_out.write_reg <= m_in.write_reg_nr;
data_in <= m_in.write_reg_data;
rc <= m_in.rc;
end if;
if d_in.write_reg_enable = '1' then
w_out.write_enable <= '1';
w_out.write_reg <= d_in.write_reg_nr;
data_in <= d_in.write_reg_data;
rc <= d_in.rc;
end if;
-- shift and byte-reverse data bytes
for i in 0 to 7 loop
k := ('0' & (to_unsigned(i, 3) xor brev_lenm1)) + ('0' & byte_offset);
perm(i) <= k(2 downto 0);
use_second(i) <= k(3);
end loop;
for i in 0 to 7 loop
j := to_integer(perm(i)) * 8;
data_permuted(i * 8 + 7 downto i * 8) <= data_in(j + 7 downto j);
end loop;
-- If the data can arrive split over two cycles, this will be correct
-- provided we don't have both sign extension and byte reversal.
negative <= (data_len(2) and data_permuted(31)) or (data_len(1) and data_permuted(15)) or
(data_len(0) and data_permuted(7));
-- trim and sign-extend
for i in 0 to 7 loop
if i < to_integer(data_len) then
if second_word = '1' then
trim_ctl(i) <= '1' & not use_second(i);
else
trim_ctl(i) <= not use_second(i) & '0';
end if;
else
trim_ctl(i) <= '0' & (negative and sign_extend);
end if;
end loop;
for i in 0 to 7 loop
case trim_ctl(i) is
when "11" =>
data_trimmed(i * 8 + 7 downto i * 8) <= data_latched(i * 8 + 7 downto i * 8);
when "10" =>
data_trimmed(i * 8 + 7 downto i * 8) <= data_permuted(i * 8 + 7 downto i * 8);
when "01" =>
data_trimmed(i * 8 + 7 downto i * 8) <= x"FF";
when others =>
data_trimmed(i * 8 + 7 downto i * 8) <= x"00";
end case;
end loop;
-- deliver to regfile
w_out.write_data <= data_trimmed;
-- test value against 0 and set CR0 if requested
if rc = '1' then
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= num_to_fxm(0);
if data_trimmed(63) = '1' then
c_out.write_cr_data <= x"80000000";
elsif or (data_trimmed(62 downto 0)) = '1' then
c_out.write_cr_data <= x"40000000";
else
c_out.write_cr_data <= x"20000000";
end if;
end if;
end process;
end;