我在这个模拟中缺少什么？

Question

我正在尝试为键盘驱动程序编写 VHDL 代码，因为我需要从 11 位向量中读取 8 位，为了清楚起见，这里是读取输入信号的过程（有信号 CLK 和数据）。

KEYBOARD_SYNC : process(CLK,SYSRESET)
        begin 
            if (CLK'event and CLK='1') then 
                KEYBOARD_CLK_VECTOR <=   KEYBOARD_CLK_VECTOR( 6 downto 0 ) & KEYBOARD_CLK;
                    RECEIVING_FLAG <='0';
                    if ( KEYBOARD_CLK_VECTOR = x"F0" ) then  -- Falling edge 
                        KEYBOARD_DATA_VECTOR <= KEYBOARD_DATA_VECTOR( 9 downto 0 ) & KEYBOARD_DATA;-- shifting 
                        BIT_COUNTER <= BIT_COUNTER + 1 ; 

                    end if; 

                    if( BIT_COUNTER = 11 ) then 
                        RECEIVING_FLAG <='1';
                        TEMP_WORD <= KEYBOARD_DATA_VECTOR( 8 downto 1 );
                        BIT_COUNTER <=0 ;
                        KEYBOARD_DATA_VECTOR <= (others =>'1');
                    end if ;

            end if ; 
end process KEYBOARD_SYNC; 

 PROCESSING  : process ( CLK ,SYSRESET ) 
        begin 
            if ( CLK'event and CLK ='1') then 
                if ( RECEIVING_FLAG = '1') then 
                    ACTUAL_WORD <= TEMP_WORD; 
                end if ;
            end if ;
end process PROCESSING;

为了运行模拟，我写了一个应该发送 0xF0 的测试平台，这个值应该保存在 ACTUAL_WORD 中，这是测试平台的一部分应该这样做:

-- Timing variables 
constant CLK_PERIOD: time := 10 ns;
constant KEYBOARD_CLK_PERIOD: time := 80 us;

...................................................



    KEYBOARD_PROCESS : process 
    BEGIN 


        -- BREAK Code 
            KEYBOARD_CLK <= '1';
            KEYBOARD_DATA <= '0';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            --Start  Bit  always 0 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';                
            KEYBOARD_DATA <= '1';           -- Sending a break code 0xF0 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 0  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 1  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 2  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 3  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_DATA<= '0';
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 4  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 5  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 6  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- 7  Bit 
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_DATA<= '1';
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- Parity Bit           
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '0';            -- Stop Bit  always 1   
        wait for (KEYBOARD_CLK_PERIOD/2);
            KEYBOARD_CLK <= '1';
        wait for (KEYBOARD_CLK_PERIOD/2);
end process KEYBOARD_PROCESS;

结果是：（可点击）

问题是我一直在阅读 0xE1 而不是 0xF0 其他所有内容都工作正常，我无法弄清楚为什么我错过了这个位。

Answer 1

将 0xF0 的周期模式读取为 0xE1 看起来像是 1 位移位，这可能是由于测试台生成时钟 (KEYBOARD_CLK) 和数据 (KEYBOARD_DATA) 在同时。

在硬件设计中，输出数据是由时钟产生的，因此时钟上升沿和新数据之间至少会有一个delta周期延迟，但目前的测试平台设计产生时钟和同时数据有：

KEYBOARD_CLK <= '1';
KEYBOARD_DATA <= '0';

因此波形看起来很熟悉，但信号流实际上缺少时钟和数据之间的增量周期延迟，因此数据比预期的波形提前一个周期就绪，导致 1 位移位。然而，这并没有显示在当前的波形视图中，这可能是令人费解的部分。 ModelSim 可以显示缺少增量循环，但这不是默认设置。

在测试台架设计中也遵循通用设计方法通常是个好主意，以便保持单一的通用设计实践，从而更容易阅读代码和波形。

所以在测试台上，做一个产生时钟的过程，然后做一个根据时钟产生数据的过程，就像硬件设计一样。这可以像这样完成：

CLK_PROCESS : process 
BEGIN 
  KEYBOARD_CLK <= '1';
  wait for (KEYBOARD_CLK_PERIOD/2);
  KEYBOARD_CLK <= '1';
  wait for (KEYBOARD_CLK_PERIOD/2);
end process;

DATA_PROCESS : process
BEGIN
  KEYBOARD_DATA <= '0';
  for i in 1 to 5 loop  -- Number of cycles with same data
      wait until rising_edge(KEYBOARD_CLK);
  end loop;
  ...
  KEYBOARD_DATA <= '1';
  for i in 1 to 5 loop  -- Number of cycles with same data
      wait until rising_edge(KEYBOARD_CLK);
  end loop;
  ...
end process;

根据所需的测试模式适当调整重复数据的循环。

我在这个模拟中缺少什么？

What I'm missing in this simulation?

vhdl

modelsim