所以我正在研究合成CPU。
这些是错误：
WARNING:Xst:1710 - FF/Latch <EXS/mem_address_0> (without init value) has a constant value of 0 in block <Top_level_component>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <EXS/mem_address_1> (without init value) has a constant value of 0 in block <Top_level_component>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <EXS/mem_address_2> (without init value) has a constant value of 0 in block <Top_level_component>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <EXS/mem_address_3> (without init value) has a constant value of 0 in block <Top_level_component>. This FF/Latch will be trimmed during the optimization process.
然后从这里级联到其他一些东西。
这是给我一个错误的零件组件：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity EX_stage is
Port( clk : in STD_LOGIC;
rst : in STD_LOGIC;
mem_opr_in : in STD_LOGIC_VECTOR (1 downto 0);
wb_opr_in : in STD_LOGIC;
out_opr_in : in STD_LOGIC;
alu_mode : in STD_LOGIC_VECTOR (3 downto 0);
in1 : in STD_LOGIC_VECTOR (7 downto 0);
in2 : in STD_LOGIC_VECTOR (7 downto 0);
ra_in : in STD_LOGIC_VECTOR (1 downto 0);
-- The Ports I'm reading from
FW_opcode : in STD_LOGIC_VECTOR (3 downto 0);
FW_ra_IN : in STD_LOGIC_VECTOR (1 downto 0);
FW_rb_IN : in STD_LOGIC_VECTOR (1 downto 0);
-- The port I'm writing to
mem_address : out STD_LOGIC_VECTOR (7 downto 0);
mem_opr_out : out STD_LOGIC_VECTOR (1 downto 0);
wb_opr_out : out STD_LOGIC;
out_opr_out : out STD_LOGIC;
alu_result : out STD_LOGIC_VECTOR (7 downto 0);
alu_mode_out : out STD_LOGIC_VECTOR (3 downto 0);
ra_out : out STD_LOGIC_VECTOR (1 downto 0);
z_flag : out STD_LOGIC;
n_flag : out STD_LOGIC);
end EX_stage;
architecture Behavioral of EX_stage is
begin
process(clk,rst)
variable temp_result: STD_LOGIC_VECTOR (7 downto 0);
begin
-- Not important... I think
end process;
process(clk,rst)
begin
if rst = '1' then
mem_address <= (others => '0');
elsif clk = '1' and clk'event then
mem_address <= FW_opcode & FW_ra_IN & FW_rb_IN;
-- If this is <= x"FF"; then it doesn't give the error
end if;
end process;
end Behavioral;
在顶级组件中我有：
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity Top_level_component is
Port ( portIN : in STD_LOGIC_VECTOR (7 downto 0);
portOUT : out STD_LOGIC_VECTOR (7 downto 0);
clk : in STD_LOGIC;
rst : in STD_LOGIC);
end Top_level_component;
architecture Behavioral of Top_level_component is
-- Only the offending components shown
component IF_stage
port( clk : in STD_LOGIC;
rst : in STD_LOGIC;
count : in STD_LOGIC_VECTOR (7 downto 0);
-- All three of these get input to ID_stage AND EX_stage
opcode : out STD_LOGIC_VECTOR (3 downto 0);
reg_a : out STD_LOGIC_VECTOR (1 downto 0);
reg_b : out STD_LOGIC_VECTOR (1 downto 0));
end component;
component ID_stage is
port( clk : in STD_LOGIC;
port_IN : in STD_LOGIC_VECTOR (7 downto 0);
opcode : in STD_LOGIC_VECTOR (3 downto 0);
ra_IN : in STD_LOGIC_VECTOR (1 downto 0);
rb_IN : in STD_LOGIC_VECTOR (1 downto 0);
zflag : in STD_LOGIC;
nflag : in STD_LOGIC;
RD1_IN : in STD_LOGIC_VECTOR (7 downto 0);
RD2_IN : in STD_LOGIC_VECTOR (7 downto 0);
count : in STD_LOGIC_VECTOR (7 downto 0);
previous_opcode : in STD_LOGIC_VECTOR (3 downto 0);
MEM_opr : out STD_LOGIC_VECTOR (1 downto 0);
WB_opr : out STD_LOGIC;
OUT_opr : out STD_LOGIC;
ALU_mode : out STD_LOGIC_VECTOR (3 downto 0);
RD1_OUT : out STD_LOGIC_VECTOR (7 downto 0);
RD2_OUT : out STD_LOGIC_VECTOR (7 downto 0);
ra_OUT : out STD_LOGIC_VECTOR (1 downto 0);
rb_OUT : out STD_LOGIC_VECTOR (1 downto 0);
new_count : out STD_LOGIC_VECTOR (7 downto 0);
set_pc : out STD_LOGIC);
end component;
component EX_stage is
port( clk : in STD_LOGIC;
rst : in STD_LOGIC;
mem_opr_in : in STD_LOGIC_VECTOR (1 downto 0);
wb_opr_in : in STD_LOGIC;
out_opr_in : in STD_LOGIC;
alu_mode : in STD_LOGIC_VECTOR (3 downto 0);
in1 : in STD_LOGIC_VECTOR (7 downto 0);
in2 : in STD_LOGIC_VECTOR (7 downto 0);
ra_in : in STD_LOGIC_VECTOR (1 downto 0);
-- The Offending ports: This is where the signals go in
FW_opcode : in STD_LOGIC_VECTOR (3 downto 0);
FW_ra_IN : in STD_LOGIC_VECTOR (1 downto 0);
FW_rb_IN : in STD_LOGIC_VECTOR (1 downto 0);
mem_address : out STD_LOGIC_VECTOR (7 downto 0);
mem_opr_out : out STD_LOGIC_VECTOR (1 downto 0);
wb_opr_out : out STD_LOGIC;
out_opr_out : out STD_LOGIC;
alu_result : out STD_LOGIC_VECTOR (7 downto 0);
alu_mode_out : out STD_LOGIC_VECTOR (3 downto 0);
ra_out : out STD_LOGIC_VECTOR (1 downto 0);
z_flag : out STD_LOGIC;
n_flag : out STD_LOGIC);
end component;
-- Signals used
signal set_pc : STD_LOGIC := '0';
signal new_count : STD_LOGIC_VECTOR (7 downto 0) := (others => '0');
signal count : STD_LOGIC_VECTOR (7 downto 0) := (others => '0');
signal IF_opcode : STD_LOGIC_VECTOR (3 downto 0) := (others => '0');
signal IF_reg_a : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal IF_reg_b : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal rd_data1 : std_logic_vector(7 downto 0) := (others => '0');
signal rd_data2 : std_logic_vector(7 downto 0) := (others => '0');
signal ID_opcode : STD_LOGIC_VECTOR (3 downto 0) := (others => '0');
signal ID_reg_a : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal ID_reg_b : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal ID_data1 : std_logic_vector(7 downto 0) := (others => '0');
signal ID_data2 : std_logic_vector(7 downto 0) := (others => '0');
signal ID_mem_opr : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal ID_wb_opr : STD_LOGIC := '0';
signal ID_out_opr : STD_LOGIC := '0';
signal EX_data1 : std_logic_vector(7 downto 0) := (others => '0');
signal EX_data2 : std_logic_vector(7 downto 0) := (others => '0');
signal EX_reg_a : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal EX_results : STD_LOGIC_VECTOR (7 downto 0) := (others => '0');
signal EX_alu_mode : STD_LOGIC_VECTOR (3 downto 0) := (others => '0');
signal mem_address : STD_LOGIC_VECTOR (7 downto 0) := (others => '0');
signal EX_mem_opr : STD_LOGIC_VECTOR (1 downto 0) := (others => '0');
signal EX_wb_opr : STD_LOGIC := '0';
signal EX_out_opr : STD_LOGIC := '0';
signal z_flag : std_logic := '0';
signal n_flag : std_logic := '0';
begin
IFS: IF_stage PORT MAP(
clk => clk,
rst => rst,
count => count,
opcode => IF_opcode,
reg_a => IF_reg_a,
reg_b => IF_reg_b);
IDS: ID_stage port map(
clk => clk,
port_IN => portIN,
opcode => IF_opcode,
ra_IN => IF_reg_a,
rb_IN => IF_reg_b,
zflag => z_flag,
nflag => n_flag,
RD1_IN => rd_data1,
RD2_IN => rd_data2,
count => count,
previous_opcode => EX_alu_mode,
MEM_opr => ID_mem_opr,
WB_opr => ID_wb_opr,
OUT_opr => ID_out_opr,
ALU_mode => ID_opcode,
RD1_OUT => ID_data1,
RD2_OUT => ID_data2,
ra_OUT => ID_reg_a,
rb_OUT => ID_reg_b,
new_count => new_count,
set_pc => set_pc);
EXS: EX_stage port map(
clk => clk,
rst => rst,
mem_opr_in => ID_mem_opr,
wb_opr_in => ID_wb_opr,
out_opr_in => ID_out_opr,
alu_mode => ID_opcode,
in1 => EX_data1,
in2 => EX_data2,
ra_in => ID_reg_a,
FW_opcode => IF_opcode,
FW_ra_IN => IF_reg_a,
FW_rb_IN => IF_reg_b,
mem_address => mem_address,
mem_opr_out => EX_mem_opr,
wb_opr_out => EX_wb_opr,
out_opr_out => EX_out_opr,
alu_result => EX_results,
alu_mode_out => EX_alu_mode,
ra_out => EX_reg_a,
z_flag => z_flag,
n_flag => n_flag);
end Behavioral;
所以在EX_stage中，当使用FW_opcode，FW_ra_IN或FW_rb_IN时，我得到了错误。我不明白。有任何想法吗？我正在尝试将输入合并到输出中吗？
答案 0 :(得分：2)
这不是错误。这是一个警告，说合成器已检测到信号始终为0，因此可以优化它。
此外，它与标题所示的锁存器无关（请注意，措辞为FF/Latch，只是说信号EXS/mem_address_0是触发器或锁存器。
这不一定是坏事，除非你知道他们也应该能够接受其他价值观。
在这种情况下，我会说好像FW_ra_IN和FW_rb_IN信号似乎总是0。如果他们应该能够接受其他值，那么请确保它们实际来自正确的地方。
在使用x"FF"替换作业时，您没有收到警告的原因是，您在重置时信号全部为0，而在重置时则为1 - 并且这些位都不是恒定的。
另请查看VHDL synthesis warning FF/Latch has a constant value of 0
答案 1 :(得分：1)
首先，你发布的是警告而不是错误......因此应该是非阻塞的。
然而，警告告诉您，mem_address（3..0）的值始终为“0”。这意味着，FW_ra_IN和FW_rb_IN始终为“0”。这些信号来自您的IF_stage块（IF_reg_a和IF_reg_b）。检查是否在IF_stage内更新这些信号。
另一件事是，在top_level块中没有使用mem_address。因此，在优化过程中可能会被合成器删除。