arm cortex-m0plus源码学习GPIO

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概述:

    Cortex-m0的integration_kit提供三个GPIO接口,其中GPIO0传输到外部供用户使用,为EXTGPIO;GPIO1是内核自己的信号,不能乱改,会崩掉;GPIO2是一些中断,这里没开中断,可以读写相应的寄存器。

1. 寄存器寻址,先看手册:

 

这里倒没什么特别,第10位为1正好对应地址0x400,为DIR寄存器,同理0x410对应中断寄存器。

对应硬件描述语言:

 // 本GPIO设备被选通、总线写、总线传输类型为连续或不连续时有效
  wire        write_trans  = HSEL & HWRITE & HTRANS[1];

  // 写信号有效时根据地址选择要写入的寄存器
  wire        nxt_gpiodata_o_wren   = write_trans & (HADDR[10   ] ==       1\'b0);
  wire        nxt_gpiodir_wren      = write_trans & (HADDR[10: 4] == 7\'b1000000);
  wire        nxt_gpiointmask_wren  = write_trans & (HADDR[10: 4] == 7\'b1000001);
//-----------------------------------------------------------------------------
// AHB register read mux
//-----------------------------------------------------------------------------

  // Drive read mux next state from word address when selected
  wire [10:4] nxt_read_mux = HSEL ? HADDR[10:4] : read_mux;

  always @(posedge HCLK or negedge HRESETn)
    if(~HRESETn)
      read_mux <= 7\'b0;           // Set select to input on reset
    else if(HREADY)               // When bus is ready
      read_mux <= nxt_read_mux;   // assign mux select next value

  wire [31:0] rdata  = (read_mux[10: 4] == 7\'b1000000)? gpiodir : (           //Offset 0x400 returns Direction Register
                       (read_mux[10: 4] == 7\'b1000001)? gpiointmask : (       //Offset 0x410 returns Interrupt Mask Register
                       (read_mux[10   ] ==       1\'b0)? gpiodata_i : 32\'b0)); //Offset 0x0 to 0x3ff returns Data Register

 2. GPIODATA读写

这个特别麻烦,手册里说的特别简洁,对应verilog一大堆。

 

首先是这个Note当初没有仔细看,后来做实验出问题也没想到,直到写这篇总结才发现,人家还给配了图,特意用来表明:gpio模块用了两个寄存器,两个寄存器是独立的。

看图说话:

 

然后总线的读数据HRDATA永远只读取mask过以后的gpio_in寄存器,总线的HWDATA永远能向gpio_out寄存器写入数据,自画丑图如下:

 

verilog:

//-----------------------------------------------------------------------------
// IO Pad registers
//-----------------------------------------------------------------------------

  assign      GPIOEN         = gpiodir;
  assign      GPIOOUT        = gpiodata_o;

  wire [31:0] nxt_gpiodata_i = GPIOIN;
// Combine bus and register values using mask for next state of Data Out Register
  wire [31:0] nxt_gpiodata_o = gpiodata_o_wren ?
                               ((HWDATA & type_mask2) | (gpiodata_o & ~type_mask2))
                               : gpiodata_o;

  always @(posedge HCLK or negedge HRESETn)
    if(~HRESETn)
      begin
        gpiodir     <= {32{1\'b0}};      // Disable all buffers on reset
        gpiointmask <= {32{1\'b0}};
        gpiodata_o  <= {32{1\'b0}};
      end
    else if (HREADY)                    // When bus is ready:
      begin
        gpiodir     <= nxt_gpiodir;     // update direction register
        gpiointmask <= nxt_gpiointmask; // update interrupt mask register
        gpiodata_o  <= nxt_gpiodata_o;  // updata data out register
      end

  always @ (posedge FCLK or negedge HRESETn)
     if(~HRESETn)
       gpiodata_i   <= {32{1\'b0}};      // Reset all outputs to zero
     else
       gpiodata_i   <= nxt_gpiodata_i;  // Sample GPIOIN continuously
assign HRDATA = rdata & type_mask2;

并且gpiodata_i这个寄存器的赋值是在FCLK时钟域(HCLK是FCLK的门控时钟,二者同频同相),这么设计为什么暂时不太懂,是害怕漏掉信号的变化?

可以看到,这里对总线读数据HRDATA和gpiodata_o寄存器的写入用的是同一组mask信号:type_mask2,这个mask信号得来不易,先看代码:

//-----------------------------------------------------------------------------
// AHB register read/write mask for byte accesses on Data register
//-----------------------------------------------------------------------------

  wire        nxt_hsize_zero = (HSIZE[1:0] == 2\'b0) & HSEL;

  always @ (hsize_zero or haddr_r or mask8 or type_mask)
    case({hsize_zero,haddr_r})
        3\'b100  : type_mask2 = {8\'h00, 8\'h00, 8\'h00, mask8};
        3\'b101  : type_mask2 = {8\'h00, 8\'h00, mask8, 8\'h00};
        3\'b110  : type_mask2 = {8\'h00, mask8, 8\'h00, 8\'h00};
        3\'b111  : type_mask2 = {mask8, 8\'h00, 8\'h00, 8\'h00};
        3\'b000,3\'b001,3\'b010,3\'b011:  type_mask2 = type_mask;
        default : type_mask2 = {32{1\'bx}};
    endcase

type_mask2的真身,可以看到,当hsize_zero为0时type_mask2直接等于type_mask,hsize_zero顾名思义,就是HSIZE为0时有效,这里有点绕,总的来说就是,当HSIZE[1:0]不为0时(字或半字访问),type_mask2=type_mask,再看type_mask

//-----------------------------------------------------------------------------
// AHB write byte address control
//-----------------------------------------------------------------------------

  // Decode term for access to least significant byte
  wire        nxt_byte0 = ( HSIZE[1] ) |
                          ( HSIZE[0] & ~HADDR[1] ) |
                          ( ~HSIZE[0] & ~HADDR[1] & ~HADDR[0] );

  // Decode term for access to byte 1
  wire        nxt_byte1 = ( HSIZE[1] ) |
                          ( HSIZE[0] & ~HADDR[1] ) |
                          ( ~HSIZE[0] & ~HADDR[1] &  HADDR[0] );

  // Decode term for access to byte 2
  wire        nxt_byte2 = ( HSIZE[1] ) |
                          ( HSIZE[0] &  HADDR[1] ) |
                          ( ~HSIZE[0] &  HADDR[1] & ~HADDR[0] );

  // Decode term for access to most significant byte
  wire        nxt_byte3 = ( HSIZE[1] ) |               //整个字-32bit访问
                          ( HSIZE[0] &  HADDR[1] ) |        //半字访问--16bit访问的情况
                          ( ~HSIZE[0] &  HADDR[1] &  HADDR[0] ); //字节访问--8bit

  always @(posedge HCLK or negedge HRESETn)
    // when bus is ready,byte[3:0] <= nxt_byte[3:0];(这里删去了,为了方便看)

  wire [31:0] type_mask = { {8{byte3}}, {8{byte2}}, {8{byte1}}, {8{byte0}} };

就是字节使能,HSIZE是总线传输规模,根据AMBA3 AHB Lite手册:

 

    HSIZE[1]=1时是32bit传输,此时type_mask=32\'hFFFF_FFFF

    HSIZE[1]=0时,看HSIZE[0]

             当HSIZE[0]=1时半字访问,再参考总线地址HADDR[1]的状态,看要访问上半字还是下半字,此时:

                        如果HADDR[1]=0,type_mask=32\'h0000_FFFF

                        如果HADDR[1]=1,type_mask=32\'hFFFF_0000

                        --而HADDR[0]的值是多少,是不care的。

            当HSIZE[0]=0时字节访问,type_mask根据HADDR[1:0]的值分别令对应的字节为1:

                        如果HADDR[1:0]=00,type_mask=32\'h0000_00FF

                        如果HADDR[1:0]=01,type_mask=32\'h0000_FF00

                        如果HADDR[1:0]=10,type_mask=32\'h00FF_0000 

                        如果HADDR[1:0]=11,type_mask=32\'hFF00_0000

以GPIO0的访问为例,如下:

  

 总的来说就是:总线字(32bit)或半字(16bit)访问GPIO时,不进行位mask,只有字节(8bit)访问时mask8才有用武之地,下面是mask8:

// For byte accesses, the mask is in HADDR[9:2]
  wire [7:0]  nxt_mask8 = (nxt_hsize_zero)? HADDR[9:2] : {8{1\'b0}};

  always @(posedge HCLK or negedge HRESETn)
    if(~HRESETn)
        mask8 <= {8{1\'b0}};      // Reset mask to FF
    else if(HREADY)
        mask8 <= nxt_mask8;      // Update AHB mask with next

其实非常简单粗暴,直接等于HADDR[9:0],并且手册里也给出了说明:

 

 

但是好死不死,给的例子也太不恰当了,写0x40000009访问第9bit,那是不是写0x40000008访问第8bit,那不是一直访问到0x40000020就行了,GPIODATA范围可是0x00~0x3ff,留这么多空间是要做啥?

并且,提供的软件程序(cm0pikmcu.h)都是这样的定义:

 1 /*--------------------- General Purpose Input and Ouptut ---------------------*/
 2 typedef union
 3 {
 4   __IO uint32_t WORD;
 5   __IO uint16_t HALFWORD[2];
 6   __IO uint8_t  BYTE[4];
 7 } GPIO_Data_TypeDef;
 8 
 9 typedef struct
10 {
11   GPIO_Data_TypeDef DATA [256];
12   GPIO_Data_TypeDef DIR;
13   uint32_t RESERVED[3];
14   GPIO_Data_TypeDef IE;
15 } GPIO_TypeDef;

访问方式:

GPIO0->DATA[0].WORD = 0x55;

没看verilog之前怎么也理解不上去这个定义,想着GPIO,不就一个寄存器吗,自己写呗,于是有了下面的代码:

*(u32 *)(0x40000400) = 0xffffffff;    //配置GPIO0->DIR寄存器为输出
*(u8 *)(0x40000000) = 0x55;           //-现象:写不进去
*(u32 *)(0x40000000) = 0x12345678;    //-现象:可以写,但总有几位写不进去。

事实上,GPIODATA的正确写入方式是:

 

不进行位屏蔽,按字节访问GPIO寄存器的正确方式:

C代码示例:

unsigned char c0, c1, c2, c3;
    *(unsigned int *)(0x40001400) = 0xffffffff;         //GPIO2设为输出
    *(unsigned int *)(0x40001000) = 0xa5a5a5a5;         //32bit写时无mask
    *(unsigned short *)(0x40001000) = 0xff3c;           //16bit写时无mask
    *(unsigned short *)(0x40001002) = 0xc300;           //16bit写时无mask         
    *(unsigned int *)(0x40001000) = 0x12345678;

    *(unsigned char *)(0x400013FC) = 0x55;              //字节写,令mask=8,8bit全部写入
    *(unsigned char *)(0x400013FD) = 0x55;
     *(unsigned char *)(0x400013FE) = 0x55;
    *(unsigned char *)(0x400013FF) = 0x55;

    c0 = *(unsigned char *)(0x400013FC);
    c1 = *(unsigned char *)(0x400013FD);
    c2 = *(unsigned char *)(0x400013FE);
    c3 = *(unsigned char *)(0x400013FF);

    *(unsigned char *)(0x400013FD)     = 0xaa;
    c0 = *(unsigned char *)(0x400013FC);
    c1 = *(unsigned char *)(0x400013FD);
    c2 = *(unsigned char *)(0x400013FE);
    c3 = *(unsigned char *)(0x400013FF);

无论是memory查看还是读取到变量都没问题。

 

并且,由于GPIO模块内部的输入、输出寄存器没有互联,如果硬件上不在GPIO模块外把输出给到输入,你是永远也无法在KEIL里看到刚刚写进去的数据的。integration_kit里对例化的三个GPIO配置如下:

 

通过COMPIKMCU.v里32个buffer实现的:

  bufif1 (EXTGPIO[31], mcu_extgpioout[31], mcu_extgpioen[31]);

  assign mcu_extgpioin = EXTGPIO;

 

GPIO1和GPIO2没有引到外部,在MCU.v的上一层,cm0p_ik_sys.v里一个赋值语句实现:

  assign sys_gpio2in           = sys_gpio2out;

 其实GPIO1还比较复杂,并不全是输出给输入,反正是core的信号,没事先别乱动,比如像这样:

  assign sys_gpio1in[23:22]    = sys_gpio1out[23:22];

  assign sys_gpio1in[21]       = sys_halted;

  assign sys_gpio1in[20]       = sys_lockup;

  assign sys_gpio1in[19]       = SLEEPDEEP;

 3. GPIO模块对总线的响应:

//-----------------------------------------------------------------------------
// AHB tie offs
//-----------------------------------------------------------------------------

  assign      HREADYOUT = 1\'b1;        // All accesses to GPIO are zero-wait
  assign      HRESP     = 1\'b0;        // Generate OK responses only

 也就是说GPIO模块永远响应OK,且完全按AHB-Lite定义的读写时序,第一个HCLK写地址,第二个HCLK读或写数据

 

 

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