分享一个硬件SPI读取TFT触摸屏程序

#include \"touch.h\" #include \"lcd.h\" #include \"delay.h\" #include \"stdlib.h\" #include \"math.h\" #include \"24cxx.h\"    #include \"spi.h\" #include \"mmc_sd.h\" #include \"led.h\" #define SPI_TOUCH   Pen_Holder Pen_Point;//定义笔实体 //默认为touchtype=0的数据. u8 CMD_RDX=0XD0; u8 CMD_RDY=0X90; // void ADS_Write_Byte(u8 num)    // {  //  u8 count=0;   //  for(count=0;count<8;count++)  //  {     //      if(num&0x80)TDIN=1;  //      else TDIN=0;   //      num<<=1;    //      TCLK=0;//上升沿有效       //      TCLK=1;      //  }               // }         //从7846/7843/XPT2046/UH7843/UH7846读取adc值       u16 ADS_Read_AD(u8 CMD)   {             u16 Num=0; #ifndef SPI_TOUCH       u8 count=0; #endif     TCLK=0;                    //先拉低时钟       TCS=0;                     //选中ADS7843 #ifdef SPI_TOUCH   SPI2_SetSpeed(SPI_SPEED_16);      SPI2_ReadWriteByte(CMD);   //发送命令字 #else     ADS_Write_Byte(CMD); #endif     delay_us(6);               //ADS7846的转换时间最长为6us     TCLK=1;                    //给1个时钟，清除BUSY               TCLK=0; #ifdef SPI_TOUCH   Num=SPI2_ReadWriteByte(0);     Num<<=8;   Num=Num|SPI2_ReadWriteByte(0);    #else     for(count=0;count<16;count++)      {                         Num<<=1;           TCLK=0;//下降沿有效                         TCLK=1;         if(DOUT)Num++;           } #endif     Num>>=4;                   //只有高12位有效.     TCS=1;                     //释放ADS7843       return(Num);   } //读取一个坐标值 //连续读取READ_TIMES次数据,对这些数据升序排列, //然后去掉最低和最高LOST_VAL个数,取平均值 #define READ_TIMES 15     //读取次数 #define LOST_VAL 5        //丢弃值 u16 ADS_Read_XY(u8 xy) {     u16 i, j;     u16 buf[READ_TIMES];     u16 sum=0;     u16 temp;     for(i=0;i     {                        buf[i]=ADS_Read_AD(xy);         }                       for(i=0;i//排序     {         for(j=i+1;j         {             if(buf[i]>buf[j])       //升序排列             {                 temp=buf[i];                 buf[i]=buf[j];                 buf[j]=temp;             }         }     }         sum=0;     for(i=LOST_VAL;i     temp=sum/(READ_TIMES-2*LOST_VAL);     return temp;   } //带滤波的坐标读取 //最小值不能少于100. u8 Read_ADS(u16 *x,u16 *y) {     u16 xtemp,ytemp;                              xtemp=ADS_Read_XY(CMD_RDX);     ytemp=ADS_Read_XY(CMD_RDY);                                                        if(xtemp<100||ytemp<100)return 0;//读数失败     *x=xtemp;     *y=ytemp;     return 1;                        //读数成功 }   //2次读取ADS7846,连续读取2次有效的AD值,且这两次的偏差不能超过 //50,满足条件,则认为读数正确,否则读数错误.      //该函数能大大提高准确度 #define ERR_RANGE 50 //误差范围 u8 Read_ADS2(u16 *x,u16 *y) {     u16 x1,y1;     u16 x2,y2;     u8 flag;        flag=Read_ADS(&x1,&y1);       if(flag==0)return(0);     flag=Read_ADS(&x2,&y2);        if(flag==0)return(0);       if(((x2<=x1&&x1//前后两次采样在+-50内     &&((y2<=y1&&y1     {         *x=(x1+x2)/2;         *y=(y1+y2)/2;         return 1;     }else return 0;   } //读取一次坐标值   //仅仅读取一次,知道PEN松开才返回!                       u8 Read_TP_Once(void) {     u8 t=0;         Pen_Int_Set(0);           //关闭中断     Pen_Point.Key_Sta=Key_Up;     Read_ADS2(&Pen_Point.X,&Pen_Point.Y);     while(PEN==0&&t<=250)     {         t++;         delay_ms(10);     };     Pen_Int_Set(1);//开启中断            if(t>=250)return 0;//按下2.5s 认为无效     else return 1;  }   ////////////////////////////////////////////////// //与LCD部分有关的函数  //画一个触摸点 //用来校准用的 void Drow_Touch_Point(u8 x,u16 y) {     LCD_DrawLine(x-12,y,x+13,y);//横线     LCD_DrawLine(x,y-12,x,y+13);//竖线     LCD_DrawPoint(x+1,y+1);     LCD_DrawPoint(x-1,y+1);     LCD_DrawPoint(x+1,y-1);     LCD_DrawPoint(x-1,y-1);     Draw_Circle(x,y,6);//画中心圈 }     //画一个大点 //2*2的点            void Draw_Big_Point(u8 x,u16 y) {           LCD_DrawPoint(x,y);//中心点     LCD_DrawPoint(x+1,y);     LCD_DrawPoint(x,y+1);     LCD_DrawPoint(x+1,y+1);         } //////////////////////////////////////////////////   //转换结果 //根据触摸屏的校准参数来决定转换后的结果,保存在X0,Y0中 void Convert_Pos(void) {                 if(Read_ADS2(&Pen_Point.X,&Pen_Point.Y))     {         Pen_Point.X0=Pen_Point.xfac*Pen_Point.X+Pen_Point.xoff;         Pen_Point.Y0=Pen_Point.yfac*Pen_Point.Y+Pen_Point.yoff;      } }      //中断,检测到PEN脚的一个下降沿. //置位Pen_Point.Key_Sta为按下状态 //中断线11线上的中断检测 void EXTI9_5_IRQHandler(void) {                        Pen_Point.Key_Sta=Key_Down;//按键按下   LED0=~LED0;       EXTI->PR=1<<5;  //清除LINE5上的中断标志位 } //PEN中断设置    void Pen_Int_Set(u8 en) {     if(en)EXTI->IMR|=1<<5;   //开启line5上的中断         else EXTI->IMR&=~(1<<5); //关闭line5上的中断    }         ////////////////////////////////////////////////////////////////////////// //此部分涉及到使用外部EEPROM,如果没有外部EEPROM,屏蔽此部分即可 #ifdef ADJ_SAVE_ENABLE //保存在EEPROM里面的地址区间基址,占用13个字节(RANGE:SAVE_ADDR_BASE~SAVE_ADDR_BASE+12) #define SAVE_ADDR_BASE 40 //保存校准参数                                            void Save_Adjdata(void) {       s32 temp;              //保存校正结果!                                           temp=Pen_Point.xfac*100000000;//保存x校正因素          AT24CXX_WriteLenByte(SAVE_ADDR_BASE,temp,4);         temp=Pen_Point.yfac*100000000;//保存y校正因素        AT24CXX_WriteLenByte(SAVE_ADDR_BASE+4,temp,4);     //保存x偏移量     AT24CXX_WriteLenByte(SAVE_ADDR_BASE+8,Pen_Point.xoff,2);                //保存y偏移量       AT24CXX_WriteLenByte(SAVE_ADDR_BASE+10,Pen_Point.yoff,2);     //保存触屏类型       AT24CXX_WriteOneByte(SAVE_ADDR_BASE+12,Pen_Point.touchtype);        temp=0X0A;//标记校准过了       AT24CXX_WriteOneByte(SAVE_ADDR_BASE+13,temp);          } //得到保存在EEPROM里面的校准值 //返回值：1，成功获取数据 //        0，获取失败，要重新校准 u8 Get_Adjdata(void) {                         s32 tempfac; //  tempfac=AT24CXX_ReadOneByte(SAVE_ADDR_BASE+13);//读取标记字,看是否校准过！           if(AT24CXX_ReadOneByte(SAVE_ADDR_BASE+13)==0X0A)//触摸屏已经校准过了                {                                                            tempfac=AT24CXX_ReadLenByte(SAVE_ADDR_BASE,4);                 Pen_Point.xfac=(float)tempfac/100000000;//得到x校准参数         tempfac=AT24CXX_ReadLenByte(SAVE_ADDR_BASE+4,4);                              Pen_Point.yfac=(float)tempfac/100000000;//得到y校准参数         //得到x偏移量         Pen_Point.xoff=AT24CXX_ReadLenByte(SAVE_ADDR_BASE+8,2);                       //得到y偏移量         Pen_Point.yoff=AT24CXX_ReadLenByte(SAVE_ADDR_BASE+10,2);                              Pen_Point.touchtype=AT24CXX_ReadOneByte(SAVE_ADDR_BASE+12);//读取触屏类型标记         if(Pen_Point.touchtype)//X,Y方向与屏幕相反         {             CMD_RDX=0X90;             CMD_RDY=0XD0;            }else                  //X,Y方向与屏幕相同         {             CMD_RDX=0XD0;             CMD_RDY=0X90;            }                return 1;        }     return 0; } #endif  // void ADJ_INFO_SHOW(u8*str) {     LCD_ShowString(40,40,\"x1:       y1:       \");     LCD_ShowString(40,60,\"x2:       y2:       \");     LCD_ShowString(40,80,\"x3:       y3:       \");     LCD_ShowString(40,100,\"x4:       y4:       \");     LCD_ShowString(40,100,\"x4:       y4:       \");     LCD_ShowString(40,120,str);                    }        //触摸屏校准代码 //得到四个校准参数 void Touch_Adjust(void) {                                    signed short pos_temp[4][2];//坐标缓存值     u8  cnt=0;      u16 d1,d2;     u32 tem1,tem2;     float fac;         cnt=0;                  POINT_COLOR=BLUE;     BACK_COLOR =WHITE;     LCD_Clear(WHITE);//清屏       POINT_COLOR=RED;//红色     LCD_Clear(WHITE);//清屏     Drow_Touch_Point(20,20);//画点1     Pen_Point.Key_Sta=Key_Up;//消除触发信号     Pen_Point.xfac=0;//xfac用来标记是否校准过,所以校准之前必须清掉!以免错误         while(1)     {         if(Pen_Point.Key_Sta==Key_Down)//按键按下了         {             if(Read_TP_Once())//得到单次按键值             {                                                  pos_temp[cnt][0]=Pen_Point.X;                 pos_temp[cnt][1]=Pen_Point.Y;                 cnt++;             }                        switch(cnt)             {                              case 1:                     LCD_Clear(WHITE);//清屏                     Drow_Touch_Point(220,20);//画点2                     break;                 case 2:                     LCD_Clear(WHITE);//清屏                     Drow_Touch_Point(20,300);//画点3                     break;                 case 3:                     LCD_Clear(WHITE);//清屏                     Drow_Touch_Point(220,300);//画点4                     break;                 case 4:  //全部四个点已经得到                     //对边相等                     tem1=abs(pos_temp[0][0]-pos_temp[1][0]);//x1-x2                     tem2=abs(pos_temp[0][1]-pos_temp[1][1]);//y1-y2                     tem1*=tem1;                     tem2*=tem2;                     d1=sqrt(tem1+tem2);//得到1,2的距离                                           tem1=abs(pos_temp[2][0]-pos_temp[3][0]);//x3-x4                     tem2=abs(pos_temp[2][1]-pos_temp[3][1]);//y3-y4                     tem1*=tem1;                     tem2*=tem2;                     d2=sqrt(tem1+tem2);//得到3,4的距离                     fac=(float)d1/d2;                     if(fac<0.95||fac>1.20||d1==0||d2==0)//不合格                     {                         cnt=0;                         LCD_Clear(WHITE);//清屏                         Drow_Touch_Point(20,20);                         ADJ_INFO_SHOW(\"ver fac is:\");                           LCD_ShowNum(40+24,40,pos_temp[0][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,40,pos_temp[0][1],4,16);   //显示数值                         LCD_ShowNum(40+24,60,pos_temp[1][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,60,pos_temp[1][1],4,16);   //显示数值                         LCD_ShowNum(40+24,80,pos_temp[2][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,80,pos_temp[2][1],4,16);   //显示数值                         LCD_ShowNum(40+24,100,pos_temp[3][0],4,16);     //显示数值                         LCD_ShowNum(40+24+80,100,pos_temp[3][1],4,16);  //显示数值                         //扩大100倍显示                         LCD_ShowNum(40,140,fac*100,3,16);//显示数值,该数值必须在95~105范围之内.                         continue;                     }                     tem1=abs(pos_temp[0][0]-pos_temp[2][0]);//x1-x3                     tem2=abs(pos_temp[0][1]-pos_temp[2][1]);//y1-y3                     tem1*=tem1;                     tem2*=tem2;                     d1=sqrt(tem1+tem2);//得到1,3的距离                                           tem1=abs(pos_temp[1][0]-pos_temp[3][0]);//x2-x4                     tem2=abs(pos_temp[1][1]-pos_temp[3][1]);//y2-y4                     tem1*=tem1;                     tem2*=tem2;                     d2=sqrt(tem1+tem2);//得到2,4的距离                     fac=(float)d1/d2;                     if(fac<0.95||fac>1.20)//不合格                     {                         cnt=0;                         LCD_Clear(WHITE);//清屏                         Drow_Touch_Point(20,20);                         ADJ_INFO_SHOW(\"hor fac is:\");                           LCD_ShowNum(40+24,40,pos_temp[0][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,40,pos_temp[0][1],4,16);   //显示数值                         LCD_ShowNum(40+24,60,pos_temp[1][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,60,pos_temp[1][1],4,16);   //显示数值                         LCD_ShowNum(40+24,80,pos_temp[2][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,80,pos_temp[2][1],4,16);   //显示数值                         LCD_ShowNum(40+24,100,pos_temp[3][0],4,16);     //显示数值                         LCD_ShowNum(40+24+80,100,pos_temp[3][1],4,16);  //显示数值                         //扩大100倍显示                         LCD_ShowNum(40,140,fac*100,3,16);//显示数值,该数值必须在95~105范围之内.                         continue;                     }//正确了                                                          //对角线相等                     tem1=abs(pos_temp[1][0]-pos_temp[2][0]);//x1-x3                     tem2=abs(pos_temp[1][1]-pos_temp[2][1]);//y1-y3                     tem1*=tem1;                     tem2*=tem2;                     d1=sqrt(tem1+tem2);//得到1,4的距离                           tem1=abs(pos_temp[0][0]-pos_temp[3][0]);//x2-x4                     tem2=abs(pos_temp[0][1]-pos_temp[3][1]);//y2-y4                     tem1*=tem1;                     tem2*=tem2;                     d2=sqrt(tem1+tem2);//得到2,3的距离                     fac=(float)d1/d2;                     if(fac<0.95||fac>1.20)//不合格                     {                         cnt=0;                         LCD_Clear(WHITE);//清屏                         Drow_Touch_Point(20,20);                         ADJ_INFO_SHOW(\"dia fac is:\");                           LCD_ShowNum(40+24,40,pos_temp[0][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,40,pos_temp[0][1],4,16);   //显示数值                         LCD_ShowNum(40+24,60,pos_temp[1][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,60,pos_temp[1][1],4,16);   //显示数值                         LCD_ShowNum(40+24,80,pos_temp[2][0],4,16);      //显示数值                         LCD_ShowNum(40+24+80,80,pos_temp[2][1],4,16);   //显示数值                         LCD_ShowNum(40+24,100,pos_temp[3][0],4,16);     //显示数值                         LCD_ShowNum(40+24+80,100,pos_temp[3][1],4,16);  //显示数值                         //扩大100倍显示                         LCD_ShowNum(40,140,fac*100,3,16);//显示数值,该数值必须在95~105范围之内.                         continue;                     }//正确了                     //计算结果                     Pen_Point.xfac=(float)200/(pos_temp[1][0]-pos_temp[0][0]);//得到xfac                           Pen_Point.xoff=(240-Pen_Point.xfac*(pos_temp[1][0]+pos_temp[0][0]))/2;//得到xoff                                                 Pen_Point.yfac=(float)280/(pos_temp[2][1]-pos_temp[0][1]);//得到yfac                     Pen_Point.yoff=(320-Pen_Point.yfac*(pos_temp[2][1]+pos_temp[0][1]))/2;//得到yoff                        if(abs(Pen_Point.xfac)>2||abs(Pen_Point.yfac)>2)//触屏和预设的相反了.                     {                         cnt=0;                         LCD_Clear(WHITE);//清屏                         Drow_Touch_Point(20,20);                         LCD_ShowString(35,110,\"TP Need readjust!\");                         Pen_Point.touchtype=!Pen_Point.touchtype;//修改触屏类型.                         if(Pen_Point.touchtype)//X,Y方向与屏幕相反                         {                             CMD_RDX=0X90;                             CMD_RDY=0XD0;                            }else                  //X,Y方向与屏幕相同                         {                             CMD_RDX=0XD0;                             CMD_RDY=0X90;                            }                         delay_ms(500);                         continue;                     }                     POINT_COLOR=BLUE;                     LCD_Clear(WHITE);//清屏                     LCD_ShowString(35,110,\"Touch Screen Adjust OK!\");//校正完成                     delay_ms(500);                     LCD_Clear(WHITE);//清屏                       return;//校正完成                            }         }     } }           //外部中断初始化函数 void Touch_Init(void) {                              RCC->APB2ENR|=1<<3;    //PB时钟使能         RCC->APB2ENR|=1<<0;    //开启辅助时钟     GPIOB->CRL&=0XFF0FFFFF;//PB5     GPIOB->CRL|=0X00800000;     GPIOB->CRH&=0XFFF0FFFF;//PB11-12     GPIOB->CRH|=0X00030000;//PB11-12     GPIOB->ODR|=1<<5|1<<12;    //PB11-12 全部上拉       SPI2_Init();      SPI2_SetSpeed(SPI_SPEED_16);     Read_ADS(&Pen_Point.X,&Pen_Point.Y);//第一次读取初始化               MY_NVIC_Init(1,0,EXTI9_5_IRQChannel,2);    RCC->APB2ENR|=0x01;    //使能io复用时钟        AFIO->EXTICR[1]|=1<<4;  //EXTI5映射到PB5     EXTI->IMR|=1<<5;        //开启line5上的中断     EXTI->EMR|=1<<5;        //不屏蔽line5上的事件     EXTI->FTSR|=1<<5;       //line5上事件下降沿触发        #ifdef ADJ_SAVE_ENABLE        AT24CXX_Init();//初始化24CXX     if(Get_Adjdata())return;//已经校准     else               //未校准?     {                                                   LCD_Clear(WHITE);//清屏       Touch_Adjust();  //屏幕校准         Save_Adjdata();      }               Get_Adjdata(); #else     LCD_Clear(WHITE);//清屏   Touch_Adjust();  //屏幕校准,带自动保存            #endif                                               //  printf(\"Pen_Point.xfac:%f\n\",Pen_Point.xfac); //  printf(\"Pen_Point.yfac:%f\n\",Pen_Point.yfac); //  printf(\"Pen_Point.xoff:%d\n\",Pen_Point.xoff); //  printf(\"Pen_Point.yoff:%d\n\",Pen_Point.yoff); }   void touch_chack_init(void) {         LCD_ShowString(CUB_X1,CUB_Y1+14,\"   1     2     3     A\");         LCD_ShowString(CUB_X1,CUB_Y2+14,\"   4     5     6     B\");         LCD_ShowString(CUB_X1,CUB_Y3+14,\"   7     8     9     C\");         LCD_ShowString(CUB_X1,CUB_Y4+14,\"   *     0     #     D\");         LCD_DrawRectangle(CUB_X1,CUB_Y1,CUB_X1+JIANGE,CUB_Y1+JIANGE);         LCD_DrawRectangle(CUB_X2,CUB_Y1,CUB_X2+JIANGE,CUB_Y1+JIANGE);         LCD_DrawRectangle(CUB_X3,CUB_Y1,CUB_X3+JIANGE,CUB_Y1+JIANGE);         LCD_DrawRectangle(CUB_X4,CUB_Y1,CUB_X4+JIANGE,CUB_Y1+JIANGE);                   LCD_DrawRectangle(CUB_X1,CUB_Y2,CUB_X1+JIANGE,CUB_Y2+JIANGE);         LCD_DrawRectangle(CUB_X2,CUB_Y2,CUB_X2+JIANGE,CUB_Y2+JIANGE);         LCD_DrawRectangle(CUB_X3,CUB_Y2,CUB_X3+JIANGE,CUB_Y2+JIANGE);         LCD_DrawRectangle(CUB_X4,CUB_Y2,CUB_X4+JIANGE,CUB_Y2+JIANGE);                   LCD_DrawRectangle(CUB_X1,CUB_Y3,CUB_X1+JIANGE,CUB_Y3+JIANGE);         LCD_DrawRectangle(CUB_X2,CUB_Y3,CUB_X2+JIANGE,CUB_Y3+JIANGE);         LCD_DrawRectangle(CUB_X3,CUB_Y3,CUB_X3+JIANGE,CUB_Y3+JIANGE);         LCD_DrawRectangle(CUB_X4,CUB_Y3,CUB_X4+JIANGE,CUB_Y3+JIANGE);                   LCD_DrawRectangle(CUB_X1,CUB_Y4,CUB_X1+JIANGE,CUB_Y4+JIANGE);         LCD_DrawRectangle(CUB_X2,CUB_Y4,CUB_X2+JIANGE,CUB_Y4+JIANGE);         LCD_DrawRectangle(CUB_X3,CUB_Y4,CUB_X3+JIANGE,CUB_Y4+JIANGE);         LCD_DrawRectangle(CUB_X4,CUB_Y4,CUB_X4+JIANGE,CUB_Y4+JIANGE);       } u8 touch_chack(void) {       u8 x2=0;     if(Pen_Point.Key_Sta==Key_Down)//触摸屏被按下         {             if(Read_TP_Once())//得到单次按键值             {                   if((Pen_Point.X0>CUB_X1&&Pen_Point.X0CUB_Y1&&Pen_Point.Y0                 {                     x2='1';                 }                               if((Pen_Point.X0>CUB_X2&&Pen_Point.X0CUB_Y1&&Pen_Point.Y0                 {                     x2='2';                 }                 if((Pen_Point.X0>CUB_X3&&Pen_Point.X0CUB_Y1&&Pen_Point.Y0                 {                     x2='3';                 }                 if((Pen_Point.X0>CUB_X4&&Pen_Point.X0CUB_Y1&&Pen_Point.Y0                 {                     x2='A';                 }                 if((Pen_Point.X0>CUB_X1&&Pen_Point.X0CUB_Y2&&Pen_Point.Y0                 {                     x2='4';                 }                               if((Pen_Point.X0>CUB_X2&&Pen_Point.X0CUB_Y2&&Pen_Point.Y0                 {                     x2='5';                 }                 if((Pen_Point.X0>CUB_X3&&Pen_Point.X0CUB_Y2&&Pen_Point.Y0                 {                     x2='6';                 }                 if((Pen_Point.X0>CUB_X4&&Pen_Point.X0CUB_Y2&&Pen_Point.Y0                 {                       x2='B';                                }                 if((Pen_Point.X0>CUB_X1&&Pen_Point.X0CUB_Y3&&Pen_Point.Y0                 {                     x2='7';                 }                               if((Pen_Point.X0>CUB_X2&&Pen_Point.X0CUB_Y3&&Pen_Point.Y0                 {                     x2='8';                 }                 if((Pen_Point.X0>CUB_X3&&Pen_Point.X0CUB_Y3&&Pen_Point.Y0                 {                     x2='9';                 }                 if((Pen_Point.X0>CUB_X4&&Pen_Point.X0CUB_Y3&&Pen_Point.Y0                 {                       x2='C';                             }                 if((Pen_Point.X0>CUB_X1&&Pen_Point.X0CUB_Y4&&Pen_Point.Y0                 {                       x2='*';                 }                   if((Pen_Point.X0>CUB_X2&&Pen_Point.X0CUB_Y4&&Pen_Point.Y0                 {                     x2='0';                 }                   if((Pen_Point.X0>CUB_X3&&Pen_Point.X0CUB_Y4&&Pen_Point.Y0                 {                       x2='#';                 }                   if((Pen_Point.X0>CUB_X4&&Pen_Point.X0CUB_Y4&&Pen_Point.Y0                 {                     x2='D';                 }                         }          }          return x2; }

在正点原子代码基础上增加硬件SPI2读取屏幕值，经过测试，速度为4.5MHZ为妙，也就是SPI2的8分频