Remove cycle in writeback

The pipeline had a cycle in writeback. Writeback is pretty
simple and unlikely to be a bottleneck, so lets remove it.

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
pull/56/head
Anton Blanchard 5 years ago committed by Anton Blanchard
parent 7bb88d5321
commit 152261fac8

@ -21,34 +21,12 @@ entity writeback is
end entity writeback;

architecture behaviour of writeback is
type reg_internal_type is record
complete : std_ulogic;
end record;
type reg_type is record
w : WritebackToRegisterFileType;
c : WritebackToCrFileType;
end record;
signal r, rin : reg_type;
signal r_int, rin_int : reg_internal_type;
begin
writeback_0: process(clk)
begin
if rising_edge(clk) then
r <= rin;
r_int <= rin_int;
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 v : reg_type;
variable v_int : reg_internal_type;
variable x : std_ulogic_vector(0 downto 0);
variable y : std_ulogic_vector(0 downto 0);
variable z : std_ulogic_vector(0 downto 0);
begin
v := r;
v_int := r_int;

x := "" & e_in.valid;
y := "" & l_in.valid;
z := "" & m_in.valid;
@ -61,51 +39,42 @@ begin

assert not(e_in.write_cr_enable = '1' and m_in.write_cr_enable = '1');

v.w := WritebackToRegisterFileInit;
v.c := WritebackToCrFileInit;
w_out <= WritebackToRegisterFileInit;
c_out <= WritebackToCrFileInit;

v_int.complete := '0';
complete_out <= '0';
if e_in.valid = '1' or l_in.valid = '1' or m_in.valid = '1' then
v_int.complete := '1';
complete_out <= '1';
end if;

if e_in.write_enable = '1' then
v.w.write_reg := e_in.write_reg;
v.w.write_data := e_in.write_data;
v.w.write_enable := '1';
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
v.c.write_cr_enable := '1';
v.c.write_cr_mask := e_in.write_cr_mask;
v.c.write_cr_data := e_in.write_cr_data;
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
v.w.write_reg := l_in.write_reg;
v.w.write_data := l_in.write_data;
v.w.write_enable := '1';
w_out.write_reg <= l_in.write_reg;
w_out.write_data <= l_in.write_data;
w_out.write_enable <= '1';
end if;

if m_in.write_reg_enable = '1' then
v.w.write_enable := '1';
v.w.write_reg := m_in.write_reg_nr;
v.w.write_data := m_in.write_reg_data;
w_out.write_enable <= '1';
w_out.write_reg <= m_in.write_reg_nr;
w_out.write_data <= m_in.write_reg_data;
end if;

if m_in.write_cr_enable = '1' then
v.c.write_cr_enable := '1';
v.c.write_cr_mask := m_in.write_cr_mask;
v.c.write_cr_data := m_in.write_cr_data;
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= m_in.write_cr_mask;
c_out.write_cr_data <= m_in.write_cr_data;
end if;

-- Update registers
rin <= v;
rin_int <= v_int;

-- Update outputs
complete_out <= r_int.complete;
w_out <= r.w;
c_out <= r.c;
end process;
end;

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