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- replaced comparator-based fill-stage with rom-based fill-stage

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git-svn-id: http://moon:8086/svn/vhdl/trunk@478 cc03376c-175c-47c8-b038-4cd826a8556b
This commit is contained in:
jens
2009-05-09 19:19:03 +00:00
parent 6449f3fa78
commit 1fe9a2c398
1 changed files with 36 additions and 35 deletions
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lib/CPUs/MIPS/src/core/mips_shifter.vhd
+36 -35
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@@ -49,7 +49,21 @@ architecture Behavioral of shifter is
signal sa_rnd : unsigned (4 downto 0);
signal fill : std_logic;
type fill_mask_rom_t is array (0 to 2*data_width-1) of unsigned(data_width-1 downto 0);
--------------------------------------------------------------------------
function gen_fill_mask_rom(data_width : natural) return fill_mask_rom_t is
variable result : fill_mask_rom_t;
begin
for i in 0 to data_width-1 loop
result(i) := (data_width-1-i downto 0 => '0') & (i-1 downto 0 => '1');
end loop;
for i in 0 to data_width-1 loop
result(data_width+i) := (i-1 downto 0 => '1') & (data_width-1-i downto 0 => '0');
end loop;
return result;
end gen_fill_mask_rom;
function rot_stage(x : unsigned; en : std_logic; stage_num : natural) return unsigned is
variable result : unsigned(x'range);
constant sa : natural := 2**stage_num;
@@ -63,52 +77,39 @@ function rot_stage(x : unsigned; en : std_logic; stage_num : natural) return uns
end rot_stage;
function rot_fill(x : unsigned; fill : std_logic; shift_right : std_logic; sa : natural) return unsigned is
variable result : unsigned(x'range) := (others => '0');
variable j : integer;
begin
if shift_right = '0' then
for i in 0 to x'left loop
if i >= sa then
result(i) := x(i);
else
result(i) := fill;
end if;
end loop;
else
j := x'left;
for i in 0 to x'left loop
if i < sa then
result(j) := fill;
else
result(j) := x(j);
end if;
j := j - 1;
end loop;
end if;
return result;
constant fill_mask_rom : fill_mask_rom_t := gen_fill_mask_rom(data_width);
signal fill_mask : unsigned(data_width-1 downto 0);
signal fill_mask_addr : unsigned(5 downto 0);
signal dout_filled : unsigned (data_width-1 downto 0);
end rot_fill;
--------------------------------------------------------------------------
begin
rot_data(0) <= din;
rot_data(0) <= din;
gen_rotate_right:
for stage in 0 to 4 generate
begin
rot_data(stage+1) <= rot_stage(rot_data(stage), sa_rnd(stage), stage);
end generate;
sa_rnd <= shift_ctrl.shamt_rnd;
fill <= shift_ctrl.shift_arith and din(data_width-1);
dout <= rot_fill(rot_data(5), fill, shift_ctrl.shift_right, to_integer(shift_ctrl.shamt_nrm)) after 5 ns;
-- dout <= rot_data(5);
sa_rnd <= shift_ctrl.shamt_rnd;
fill <= shift_ctrl.shift_arith and din(data_width-1);
fill_mask_addr <= shift_ctrl.shift_right & shift_ctrl.shamt_nrm;
fill_mask <= fill_mask_rom(to_integer(fill_mask_addr));
proc_fill_neu:
process(fill_mask, fill, rot_data(5))
begin
if fill = '1' then
dout_filled <= rot_data(5) or fill_mask;
else
dout_filled <= rot_data(5) and not fill_mask;
end if;
end process;
dout <= dout_filled after 5 ns;
--------------------------------------------------------------------------
end Behavioral;