CCS5.4+Proteus8的F28027实践课十、SPI / 开普饭

刚刚我们已经把SPI的理论知识部分讲完了，现在我们根据寄存器和时序图来写程序了。
首先，既然是SPI，肯定是复用了GPIO，我们先回顾下GPIO引脚说明：

从上面可以看到我们这次实践课需要复用GPIO16/GPIO17/GPIO18/GPIO19四个引脚。
然后我们来看下寄存器，这里我们只看总体寄存器结构，具体寄存器位大家自己下去了解，我们就不浪费章节了。

我们在上节课中提到过寄存器的初始化，不知道大家还有没有印象：
初始化SPI配置：
1、SPI SW RESET bit (SPICCR.7)清空，强制SPI处于复位状态；
2、初始化SPI的配置、模式、比特率和引脚；
3、SPI SW RESET bit (SPICCR.7)置1，将SPI从复位状态释放；
4、写数据到SPIDAT or SPITXBUF；
5、当传输完成后，也就是SPISTS.6 = 1，从SPIRXBUF读出有用数据；

看到这里，大家应该大概知道往哪个方向写了吧，来，我们先来一个简单的，不使用中断方式的回环测试，方便仿真，来一起摸索下SPI的初始化函数：

void InitSpi(void)
{
    EALLOW;
    SpiaRegs.SPICCR.bit.SPISWRESET=0; // Reset SPI
    SpiaRegs.SPICCR.bit.SPILBK=1;     //loopback
    SpiaRegs.SPICCR.bit.SPICHAR=7;    //8 characters
    SpiaRegs.SPICTL.bit.MASTER_SLAVE=1; //master mode
    SpiaRegs.SPICTL.bit.TALK=1;         // enable transmission
    SpiaRegs.SPISTS.bit.BUFFULL_FLAG=0;
    SpiaRegs.SPISTS.bit.INT_FLAG=0;
    SpiaRegs.SPISTS.bit.OVERRUN_FLAG=0;
    SpiaRegs.SPIBRR=99;           // Baud rate初始化在一个低速的状态下
    SpiaRegs.SPIPRI.all=0x0010;
    SpiaRegs.SPICCR.bit.SPISWRESET=1;  // Enable SPI
    EDIS;
}

引脚初始化函数：

void InitSpiaGpio()
{

   EALLOW;

/* Enable internal pull-up for the selected pins */
// Pull-ups can be enabled or disabled by the user.
// This will enable the pullups for the specified pins.
// Comment out other unwanted lines.

    GpioCtrlRegs.GPAPUD.bit.GPIO16 = 0;   // Enable pull-up on GPIO16 (SPISIMOA)
    GpioCtrlRegs.GPAPUD.bit.GPIO17 = 0;   // Enable pull-up on GPIO17 (SPISOMIA)
    GpioCtrlRegs.GPAPUD.bit.GPIO18 = 0;   // Enable pull-up on GPIO18 (SPICLKA)
    GpioCtrlRegs.GPAPUD.bit.GPIO19 = 0;   // Enable pull-up on GPIO19 (SPISTEA)

/* Set qualification for selected pins to asynch only */
// This will select asynch (no qualification) for the selected pins.
// Comment out other unwanted lines.

    GpioCtrlRegs.GPAQSEL2.bit.GPIO16 = 3; // Asynch input GPIO16 (SPISIMOA)
    GpioCtrlRegs.GPAQSEL2.bit.GPIO17 = 3; // Asynch input GPIO17 (SPISOMIA)
    GpioCtrlRegs.GPAQSEL2.bit.GPIO18 = 3; // Asynch input GPIO18 (SPICLKA)
    GpioCtrlRegs.GPAQSEL2.bit.GPIO19 = 3; // Asynch input GPIO19 (SPISTEA)

/* Configure SPI-A pins using GPIO regs*/
// This specifies which of the possible GPIO pins will be SPI functional pins.
// Comment out other unwanted lines.

    GpioCtrlRegs.GPAMUX2.bit.GPIO16 = 1; // Configure GPIO16 as SPISIMOA
    GpioCtrlRegs.GPAMUX2.bit.GPIO17 = 1; // Configure GPIO17 as SPISOMIA
    GpioCtrlRegs.GPAMUX2.bit.GPIO18 = 1; // Configure GPIO18 as SPICLKA
    GpioCtrlRegs.GPAMUX2.bit.GPIO19 = 1; // Configure GPIO19 as SPISTEA

    EDIS;
}

初始化写完了，现在还剩两个最终要的函数，也就是读和写，这个可以根据时序图参考3线模式来写：
首先是写操作：

//---------------------------------------------------------------------------
// SPI_write:
//---------------------------------------------------------------------------
// This function is based on the TX BUF FULL FLAG's value
//if the value is 1,stating the a character is written to the SPI Transmit buffer SPITXBUF
//else if the value is 0,stating the shifting out of a previous character is complete
void SPI_write(unsigned int data)
{
    data=data<<8;             //transmission is right-justified
    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG);       //the shifting out of a previous character is complete
    SpiaRegs.SPITXBUF=data;
}

因为我们没有使用中断了，所以直接判断TX BUF FULL FLAG的值，当为1时，说明还是写，为0说明已经完全写完了。
说完了写操作，那读就好理解了，直接贴程序

//---------------------------------------------------------------------------
// SPI_read:
//---------------------------------------------------------------------------
// This function is based on the INT_FLAG's value
//if the value is 1,stating a receive or transmit operation completes before the previous character has been read from the buffer
unsigned int SPI_read()
{
    unsigned int data;
    while(!SpiaRegs.SPISTS.bit.INT_FLAG);
    data=SpiaRegs.SPIRXBUF&0x00ff;
    return data;
}

好，函数都准备完成了，我们现在写程序测试下

void main(void)
{
    unsigned int temp;

// Step 1. Initialize System Control:
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the DSP2802x_SysCtrl.c file.
   InitSysCtrl();

// Step 2. Initalize GPIO:
// This example function is found in the DSP2802x_Gpio.c file and
// illustrates how to set the GPIO to it's default state.
//   InitGpio();

// Step 3. Clear all interrupts and initialize PIE vector table:
// Disable CPU interrupts
   DINT;

// Initialize PIE control registers to their default state.
// The default state is all PIE interrupts disabled and flags
// are cleared.
// This function is found in the DSP2802x_PieCtrl.c file.
   InitPieCtrl();

// Disable CPU interrupts and clear all CPU interrupt flags:
   IER = 0x0000;
   IFR = 0x0000;

// Initialize the PIE vector table with pointers to the shell Interrupt
// Service Routines (ISR).
// This will populate the entire table, even if the interrupt
// is not used in this example.  This is useful for debug purposes.
// The shell ISR routines are found in DSP2802x_DefaultIsr.c.
// This function is found in DSP2802x_PieVect.c.
   InitPieVectTable();

// Step 4. Initialize all the Device Peripherals:
// This function is found in DSP2802x_InitPeripherals.c
// InitPeripherals(); // Not required for this example

// Step 5. User specific code:

   InitSpiGpio();
   InitSpi();

   SPI_write(0x0055);
   temp = SPI_read();

   while(1);
}

主函数是不是非常简单，呵呵，下载调试下

成功，呵呵，真高兴，示例程序我等下马上上传到CSDN下载库和qq群。
又是一点了，洗洗睡了，周末部门去旅游，我会带上电脑，把SCI章节的理论知识先学习了，等我周末晚上回来，就马上把实践课补上。
F28027菜鸟交流qq群107691092

CCS5.4+Proteus8的F28027实践课十、SPI

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