CPLD 与STM32 单字节数据访问code

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#stm32 #cpld

于 2014-08-16 12:34:37 首次发布

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本文深入分析了在使用STM32微控制器时，扩展不同类型的SRAM可能引发的问题，特别是没有正确处理片选信号的情况，可能会导致系统运行异常或不稳定。文章详细阐述了可能导致问题的机制，并提供了预防措施。

-- Tool versions: ISE 12.3
-- Description:
--
-- Dependencies:
--
-- Revision:
-- Revision 0.01 - File Created
-- Additional Comments:
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

use IEEE.std_logic_unsigned.all;

entity xxx-world is
port (
     DATA:    inout STD_LOGIC_VECTOR (7 downto 0 );
     ADD:     in     STD_LOGIC_VECTOR (7 downto 0 );
     WR:      in     STD_LOGIC;
     RD:      in     STD_LOGIC;
     CLK_4M: in     STD_LOGIC;
     MCLK:    out    STD_LOGIC;
              SYNC_PD0:out    STD_LOGIC;
     SYNC_PD1:out    STD_LOGIC;
     CPLD_RST:in     STD_LOGIC;
     AD_CS0: out    STD_LOGIC;
     AD_CS1: out    STD_LOGIC;
     FSMC_NE3:in     STD_LOGIC

);
end xxx-world;

architecture Behavioral of xxx-world is

constant PARAM_ADD0:    std_logic_vector:="00000000";   --设备属性0-9对应的地址（ADDM）
constant PARAM_ADD1:    std_logic_vector:="00000010";
constant PARAM_ADD2:    std_logic_vector:="00000100";
constant PARAM_ADD3:    std_logic_vector:="00000110";
constant PARAM_ADD4:    std_logic_vector:="00001000";
constant PARAM_ADD5:    std_logic_vector:="00001010";
constant PARAM_ADD6:    std_logic_vector:="00001100";
constant PARAM_ADD7:    std_logic_vector:="00001110";
constant PARAM_ADD8:    std_logic_vector:="00010000";
constant PARAM_ADD9:    std_logic_vector:="00010010";

constant PARAM_DATA0:   std_logic_vector:="00001010"; --0x0c
constant PARAM_DATA1:   std_logic_vector:="00000101"; --0x05
constant PARAM_DATA2:   std_logic_vector:="00001001"; --0x09
constant PARAM_DATA3:   std_logic_vector:="00001111"; --0x0f
constant PARAM_DATA4:   std_logic_vector:="10100000";
constant PARAM_DATA5:   std_logic_vector:="01010000";
constant PARAM_DATA6:   std_logic_vector:="10000000";
constant PARAM_DATA7:   std_logic_vector:="11100000";
constant PARAM_DATA8:   std_logic_vector:="11110000";
constant PARAM_DATA9:   std_logic_vector:="10101010";

signal RESET: std_logic;
signal S_MCLK: std_logic;

signal   FRE_COUNT :    std_logic_vector(19 downto 0);
signal   MCLK_COUNT:    std_logic_vector(19 downto 0);
signal   SPI_EN:        std_logic_vector(1 downto 0);
signal   MCLK_START:    std_logic;
signal   PD_EN:         std_logic_vector(1 downto 0);
-- signal   S_AD_INT:      std_logic;
-- signal   INT_COUNT:     std_logic_vector(3 downto 0);

begin
--/*******************************************************************/
--/*系统复位
--/*******************************************************************/
SystemReset_Process:
Process(WR,ADD)
begin
    if WR='0' and ADD ="01000000" then
     RESET <= DATA(0);
  end if;
end process;
--/*******************************************************************/
--/*读系统属性设备号
--/*******************************************************************/
SysParam_Process:
process(RD,ADD)
begin
  if RD='0' and ADD= PARAM_ADD0 then
   DATA <= PARAM_DATA0;
--   D_AL <= FRE_COUNT(7 downto 0);
  elsif RD='0' and ADD= PARAM_ADD1 then
   DATA <= PARAM_DATA1;
--         D_AL <= FRE_COUNT(15 downto 8);
  elsif RD='0' and ADD= PARAM_ADD2 then
   DATA <= PARAM_DATA2;
--         D_AL <= "0000"&FRE_COUNT(19 downto 16);
  elsif RD='0' and ADD= PARAM_ADD3 then
   DATA <= PARAM_DATA3;
  elsif RD='0' and ADD= PARAM_ADD4 then
   DATA <= PARAM_DATA4;
  elsif RD='0' and ADD= PARAM_ADD5 then
   DATA <= PARAM_DATA5;
  elsif RD='0' and ADD= PARAM_ADD6 then
   DATA <= PARAM_DATA6;
  elsif RD='0' and ADD= PARAM_ADD7 then
   DATA <= PARAM_DATA7;
  elsif RD='0' and ADD= PARAM_ADD8 then
   DATA <= PARAM_DATA8;
  elsif RD='0' and ADD= PARAM_ADD9 then
   DATA <= PARAM_DATA9;
  else
   DATA <= "ZZZZZZZZ";
  end if;
end process;

--/*******************************************************************/
--/*Frequency Counter
--/*******************************************************************/
FreCount_Process:
-- process(RESET,WR,ADDH,ADDM,ADD_LATCH)
process(WR,ADD)
begin
--  if RESET='0' then
--   FRE_COUNT <= "00000000000000000000";
--   MCLK_START <= '0';
--     PD_EN <= "00";
--      els
  if WR='0'    and ADD="00100000" then --0X20
     FRE_COUNT(7 downto 0) <= DATA;
  elsif WR='0' and ADD="00100010" then --0X22
     FRE_COUNT(15 downto 8) <= DATA;
  elsif WR='0' and ADD="00100100" then --0X24
     FRE_COUNT(19 downto 16) <= DATA(3 downto 0);
  elsif WR='0' and ADD="00101010" then --0X2A
     MCLK_START <= DATA(0);
  elsif WR='0' and ADD="00111010" then --0X3A
     PD_EN <= DATA(1 downto 0);
  end if;
end process;
MCLK_Process:
process(CLK_4M,MCLK_START)
begin
    if MCLK_START = '0' then
     MCLK_COUNT <= "00000000000000000000";
--   S_MCLK <= '0';
  elsif rising_edge(CLK_4M) then
     if MCLK_COUNT = FRE_COUNT then
      MCLK_COUNT <= "00000000000000000000";
--    S_MCLK <= not S_MCLK;
   else
      MCLK_COUNT <= MCLK_COUNT + '1';
   end if;

   if MCLK_COUNT <= ('0'& FRE_COUNT(19 downto 1) ) then
    S_MCLK <= '1';
   else
    S_MCLK <= '0';
   end if;
    end if;
  MCLK <= S_MCLK;
end process;
--/*******************************************************************/
--/*SYNC PD
--/*******************************************************************/
   PD_Process:
process(PD_EN)
begin
  if PD_EN = "01" then
     SYNC_PD0 <= '1';            --high power on
   SYNC_PD1 <= '0';
  elsif PD_EN = "10" then
     SYNC_PD0 <= '0';
   SYNC_PD1 <= '1';
  elsif PD_EN = "11" then
     SYNC_PD0 <= '1';
   SYNC_PD1 <= '1';
  elsif PD_EN = "00" then
     SYNC_PD0 <= '0';
   SYNC_PD1 <= '0';
      end if;
end process;

--/*******************************************************************/
--/*SPI Select
--/*******************************************************************/
   SPI_Process:
   process(RESET,WR,ADD)
   begin
      if RESET = '0' then
         SPI_EN <= "00";
      elsif WR='0' and ADD="00110000" then   --0x30
     SPI_EN <= DATA(1 downto 0);
      end if;
      if SPI_EN = "01" then
         AD_CS0 <='0';                  --low select
         AD_CS1 <='1';
      elsif SPI_EN = "10" then
         AD_CS0 <='1';
         AD_CS1 <='0';
  elsif SPI_EN = "11" then
         AD_CS0 <='1';
         AD_CS1 <='1';
      else
     AD_CS0 <='1';
         AD_CS1 <='1';
      end if;
   end process;