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microwatt/writeback.vhdl

147 lines
5.2 KiB
VHDL

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 Loadstore1ToWritebackType;
fp_in : in FPUToWritebackType;
w_out : out WritebackToRegisterFileType;
c_out : out WritebackToCrFileType;
complete_out : out instr_tag_t
);
end entity writeback;
architecture behaviour of writeback is
begin
writeback_0: process(clk)
variable x : std_ulogic_vector(0 downto 0);
variable y : std_ulogic_vector(0 downto 0);
variable w : std_ulogic_vector(0 downto 0);
begin
if rising_edge(clk) then
-- Do consistency checks only on the clock edge
x(0) := e_in.valid;
y(0) := l_in.valid;
w(0) := fp_in.valid;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) +
to_integer(unsigned(w))) <= 1 severity failure;
x(0) := e_in.write_enable or e_in.exc_write_enable;
y(0) := l_in.write_enable;
w(0) := fp_in.write_enable;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) +
to_integer(unsigned(w))) <= 1 severity failure;
w(0) := e_in.write_cr_enable;
x(0) := (e_in.write_enable and e_in.rc);
y(0) := fp_in.write_cr_enable;
assert (to_integer(unsigned(w)) + to_integer(unsigned(x)) +
to_integer(unsigned(y))) <= 1 severity failure;
assert not (e_in.valid = '1' and e_in.instr_tag.valid = '0') severity failure;
assert not (l_in.valid = '1' and l_in.instr_tag.valid = '0') severity failure;
assert not (fp_in.valid = '1' and fp_in.instr_tag.valid = '0') severity failure;
end if;
end process;
writeback_1: process(all)
variable cf: std_ulogic_vector(3 downto 0);
variable zero : std_ulogic;
variable sign : std_ulogic;
variable scf : std_ulogic_vector(3 downto 0);
begin
w_out <= WritebackToRegisterFileInit;
c_out <= WritebackToCrFileInit;
complete_out <= instr_tag_init;
if e_in.valid = '1' then
complete_out <= e_in.instr_tag;
elsif l_in.valid = '1' then
complete_out <= l_in.instr_tag;
elsif fp_in.valid = '1' then
complete_out <= fp_in.instr_tag;
end if;
if e_in.exc_write_enable = '1' then
w_out.write_reg <= e_in.exc_write_reg;
w_out.write_data <= e_in.exc_write_data;
w_out.write_enable <= '1';
else
if e_in.write_enable = '1' then
w_out.write_reg <= e_in.write_reg;
w_out.write_data <= e_in.write_data;
w_out.write_enable <= '1';
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 e_in.write_xerc_enable = '1' then
c_out.write_xerc_enable <= '1';
c_out.write_xerc_data <= e_in.xerc;
end if;
if fp_in.write_enable = '1' then
w_out.write_reg <= fp_in.write_reg;
w_out.write_data <= fp_in.write_data;
w_out.write_enable <= '1';
end if;
if fp_in.write_cr_enable = '1' then
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= fp_in.write_cr_mask;
c_out.write_cr_data <= fp_in.write_cr_data;
end if;
if l_in.write_enable = '1' then
w_out.write_reg <= l_in.write_reg;
w_out.write_data <= l_in.write_data;
w_out.write_enable <= '1';
end if;
if l_in.rc = '1' then
-- st*cx. instructions
scf(3) := '0';
scf(2) := '0';
scf(1) := l_in.store_done;
scf(0) := l_in.xerc.so;
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= num_to_fxm(0);
c_out.write_cr_data(31 downto 28) <= scf;
end if;
-- Perform CR0 update for RC forms
-- Note that loads never have a form with an RC bit, therefore this can test e_in.write_data
if e_in.rc = '1' and e_in.write_enable = '1' then
zero := not (or e_in.write_data(31 downto 0));
if e_in.mode_32bit = '0' then
sign := e_in.write_data(63);
zero := zero and not (or e_in.write_data(63 downto 32));
else
sign := e_in.write_data(31);
end if;
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= num_to_fxm(0);
cf(3) := sign;
cf(2) := not sign and not zero;
cf(1) := zero;
cf(0) := e_in.xerc.so;
c_out.write_cr_data(31 downto 28) <= cf;
end if;
end if;
end process;
end;