VHDL中的语法错误 - 在case语句中

Question

我对VHDL非常陌生。在这里我有一个计算两个数字的GCD的程序。我有一堆案例和if语句。 当我试图模拟，它给了我6个错误没有太多的描述

错误： 'U：\ GCD.dwv' 错误0行41：语法错误 'U：\ GCD.dwv' 错误0线43 ：语法错误

有趣的是他们每个人都被2行隔开。所以它从第33行开始，并且上升到43，同样的错误。它在“S3 =>”时开始。 这是我的代码。谢谢！

library IEEE; 
use IEEE.std_logic_1164.all; 
use IEEE.std_logic_arith.all; 

entity GCD is 
    port(clk, st : in std_logic; d1, d2 : in std_logic_vector(15 downto 0); dout : out std_logic_vector(15 downto 0); rdy : out std_logic); 
end GCD; 


architecture behav of GCD is 
type state is (S0, S1, S2, S3, S4, S5, S6, S7); 
signal new_state : state; 
signal eq, It, eq1 : boolean; 

begin 
     --State Transition Process 
    process is 
    variable curr_state : state := S0; 
    begin 

    if clk ='1' then 
     case curr_state is 
      when S0 => 
       if st='1' then curr_state := S1; 
       end if; 
      when S1 => 
       curr_state := S2; 
      when S2 => 
       if eq then curr_state := S7; 
       else if It then curr_state := S4; 
       else if not(eq or It) then curr_state := S3; 
       end if; 
      when S3 => 
       curr_state := S4; 
      when S4 => 
       curr_state := S5; 
      when S5 => 
       if eq1 then curr_state := S7; 
       else curr_state := S6; 
       end if; 
      when S6 => 
       curr_state := S1; 
      when S7 => 
       if not(st) then curr_state := S0; 
       end if; 
     end case; 
     new_state <= curr_state; 
    end if; 
    wait on clk; 
end process; 


-- Asserted Outputs Process: 

process is 

variable M, N, T, dout_val : std_logic_vector(15 downto 0); 
variable rdy_val : std_logic; 
variable eq_val, It_val, eq1_val : boolean; 
begin 

    rdy_val := '0'; 
    case new_state is 
     when S0 => 
      M := d1; N := d2; 
     when S1 => 
      eq_val := M=N; It_val := to_integer(M) < to_integer(N); 
     when S2 => 
     when S3 => 
      M := T; M := N; N := T; 
     when S4 => 
      eq1_val := to_integer(M) = 1; 
     when S5 => 
     when S6 => 
      N := N - M; 
     when S7 => 
      rdy_val := '1'; dout_val := M; 
    end case; 
    eq <= eq_val; 
    It <= It_val; 
    eq1 <= eq1_val; 
    rdy <= rdy_val; 
    dout <= dout_val; 
    wait on new_state; 
end process; 


end behav; 

Answer 1

而不是else if使用elsif。潜伏在那里的可能会有更多的错误。

use ieee.std_logic_unsigned.all; -- because you use std_logic_arith 

...状态转变过程：

 when S7 => 
      if st = '0' then -- not (st) then 
       curr_state := S0; 
      end if; 

...输出过程：

 when S1 => 
      eq_val := M = N; 
      -- It_val := to_integer(M) < to_integer(N); 
      It_val := M < N; 

     when S4 => 
      -- eq1_val := to_integer(M) = 1; 
      eq_val := conv_integer(M) = 1; 

VHDL有分隔明确要求，剩下的就是风格。由于缺乏一致的风格，您的代码需要仔细阅读。

其他读者无疑会建议使用使用的软件包numeric_std，如果你使用的是VHDL -2008兼容的工具，包装std_numeric_unsigned，而不是新思 - 非标准使用包std_logic_arith和std_logic_unsigned的。您尝试使用to_integer是从std_logic_unsigned。

Answer 2

我想给你举例说明我如何使用写一个FSM。我希望它可以用于你的目的。

when S2 => 
    if eq then curr_state := S7; 
    else if It then curr_state := S4; 
    else if not(eq or It) then curr_state := S3; 
    end if; 

变为：

LIBRARY ieee; 
USE ieee.std_logic_1164.ALL; 
USE ieee.numeric_std.ALL; 

ENTITY FSM IS 
    PORT(
    Clk   : IN STD_LOGIC; 
    nResetLogic : IN STD_LOGIC; 
    A    : IN STD_LOGIC; 
    B    : IN STD_LOGIC; 
    OUT_A    : OUT STD_LOGIC; 
    OUT_B    : OUT STD_LOGIC; 
    ); 
END ENTITY FSM; 

ARCHITECTURE RTL OF FSM IS 

-- states 
TYPE state IS (stateA, stateB, stateC); 
signal present_state, next_state : state; 

-- Segnals for outputs 
signal s_OUT_A    : STD_LOGIC; 
signal s_OUT_B    : STD_LOGIC; 



BEGIN 

    -- Sequential section 

    PROCESS (nResetLogic, Clk) 
    BEGIN 

    IF nResetLogic = '0' THEN 
     present_state <= stateA; 
    ELSIF (RISING_EDGE(Clk)) THEN 
     present_state <= next_state; 
    END IF; 

    END PROCESS; 

    -- Comb Section 

    PROCESS (A,B,present_state) 

    BEGIN 
    --defaults 
    s_OUT_A <= '0';   
    s_OUT_B <= '0'; 

    next_state <= present_state; 

    CASE present_state IS 
     WHEN stateA => 
      -- state definition 
      IF (B = '0' AND A = '1') THEN 
       next_state <= stateB; 
      ELSIF (B = '1' AND A = '0') THEN 
       next_state <= stateC; 
      END IF; 

      --output definition 
      s_OUT_A <= '0';   
      s_OUT_B <= '1'; 


     WHEN stateB => 
      -- state definition 
      IF (B = '1' AND A = '1') THEN 
       next_state <= stateC; 
      ELSIF (B = '1' AND A = '0') THEN 
       next_state <= stateA; 

      END IF; 

      --output definition 
      s_OUT_A <= '1';   
      s_OUT_B <= '1'; 


     WHEN stateC => 
      -- state definition 
      IF (B = '0' AND A = '1') THEN 
       next_state <= statoA; 
      ELSIF (B = '1' AND A = '0') THEN 
       next_state <= statonB; 
      END IF; 

      --output definition 
      --get defaults   

    END CASE; 

    END PROCESS; 

    -- Outputs 
    OUT_A <= s_OUT_A;   
    OUT_B <= s_OUT_B; 

END ARCHITECTURE RTL; 

Answer 3

有上面的编码风格的一些很好的意见，而是直接回答原来的问题，当你布置你的“如果”语句好听你的错误是相当清楚的

when S2 => 
    if eq then 
     curr_state := S7; 
    else 
     if It then 
      curr_state := S4; 
     else 
      if not(eq or It) then 
       curr_state := S3; 
      end if; 

正如您所看到的，有两个缺少'end if'语句。很多时候，你会发现FPGA工具产生的错误实际上是由前一行产生的。在这种情况下，“when S3 =>”这一行会产生错误，因为在“else”块中间本身不能有“when”。