AXI quad SPI没有输出

AXI quad SPI没有输出（已解决）

在使用ZYNQ的AXI quad SPI时遇到以下问题：
使用loopback可以成功，但是使用示波器测量引脚却没有输出。

问题描述：

最近在用ZYNQ的AXI quad SPI拓展接口，却遇到了这个问题：
添加AXI quad SPI核，编译完毕后。使用官方例程，loopback模式可以跑通，但是正常输出模式无法工作，且用示波器测试引脚输出没有波形。

IP核AXI quad SPI的设置如下：

程序为AXI quad SPI官方的 xspi_polled_example：

/***************************** Include Files *********************************/

#include "xparameters.h"	/* XPAR parameters */
#include "xspi.h"		/* SPI device driver */
#include "xspi_l.h"
#include "xil_printf.h"

/************************** Constant Definitions *****************************/

/*
 * The following constants map to the XPAR parameters created in the
 * xparameters.h file. They are defined here such that a user can easily
 * change all the needed parameters in one place.
 */
#define SPI_DEVICE_ID		XPAR_SPI_0_DEVICE_ID

/*
 *  This is the size of the buffer to be transmitted/received in this example.
 */
#define BUFFER_SIZE		12


/**************************** Type Definitions *******************************/

/*
 * The following data type is used to send and receive data on the SPI
 * interface.
 */
typedef u8 DataBuffer[BUFFER_SIZE];


/***************** Macros (Inline Functions) Definitions *********************/


/************************** Function Prototypes ******************************/

int SpiPolledExample(XSpi *SpiInstancePtr, u16 SpiDeviceId);

/************************** Variable Definitions *****************************/

/*
 * The instances to support the device drivers are global such that the
 * are initialized to zero each time the program runs.
 */
static XSpi  SpiInstance;	 /* The instance of the SPI device */

/*
 * The following variables are used to read and write to the  Spi device, they
 * are global to avoid having large buffers on the stack.
 */
u8 ReadBuffer[BUFFER_SIZE];
u8 WriteBuffer[BUFFER_SIZE];


/*****************************************************************************/
/**
*
* Main function to call the Spi Polled example.
*
* @param	None
*
* @return	XST_SUCCESS if successful, otherwise XST_FAILURE.
*
* @note		None
*
******************************************************************************/
int main(void)
{
	int Status;

	/*
	 * Run the Spi Polled example.
	 */
	Status = SpiPolledExample(&SpiInstance, SPI_DEVICE_ID);
	if (Status != XST_SUCCESS) {
		xil_printf("Spi polled Example Failed\r\n");
		return XST_FAILURE;
	}

	xil_printf("Successfully ran Spi polled Example\r\n");
	return XST_SUCCESS;
}

/*****************************************************************************/
/**
*
* This function does a minimal test on the Spi device and driver as a
* design example. The purpose of this function is to illustrate how to use
* the XSpi component using the polled mode.
*
* This function sends data and expects to receive the same data.
*
*
* @param	SpiInstancePtr is a pointer to the instance of Spi component.
* @param	SpiDeviceId is the Device ID of the Spi Device and is the
*		XPAR_<SPI_instance>_DEVICE_ID value from xparameters.h.
*
* @return	XST_SUCCESS if successful, otherwise XST_FAILURE.
*
* @note
*
* This function contains an infinite loop such that if the Spi device is not
* working it may never return.
*
******************************************************************************/
int SpiPolledExample(XSpi *SpiInstancePtr, u16 SpiDeviceId)
{
	int Status;
	u32 Count;
	u8 Test;
	XSpi_Config *ConfigPtr;	/* Pointer to Configuration data */

	/*
	 * Initialize the SPI driver so that it is  ready to use.
	 */
	ConfigPtr = XSpi_LookupConfig(SpiDeviceId);
	if (ConfigPtr == NULL) {
		return XST_DEVICE_NOT_FOUND;
	}

	Status = XSpi_CfgInitialize(SpiInstancePtr, ConfigPtr,
				  ConfigPtr->BaseAddress);
	if (Status != XST_SUCCESS) {
		return XST_FAILURE;
	}

	/*
	 * Perform a self-test to ensure that the hardware was built correctly.
	 */
	Status = XSpi_SelfTest(SpiInstancePtr);
	if (Status != XST_SUCCESS) {
		return XST_FAILURE;
	}

	/*
	 * Run loopback test only in case of standard SPI mode.
	 */
	if (SpiInstancePtr->SpiMode != XSP_STANDARD_MODE) {
		return XST_SUCCESS;
	}

	/*
	 * Set the Spi device as a master and in loopback mode.
	 */
	Status = XSpi_SetOptions(SpiInstancePtr, XSP_MASTER_OPTION |
 					XSP_LOOPBACK_OPTION);
	if (Status != XST_SUCCESS) {
		return XST_FAILURE;
	}


	/*
	 * Start the SPI driver so that the device is enabled.
	 */
	XSpi_Start(SpiInstancePtr);

	/*
	 * Disable Global interrupt to use polled mode operation
	 */
	XSpi_IntrGlobalDisable(SpiInstancePtr);

	/*
	 * Initialize the write buffer with pattern to write, initialize the
	 * read buffer to zero so it can be verified after the read, the
	 * Test value that is added to the unique value allows the value to be
	 * changed in a debug environment.
	 */
	Test = 0x10;
	for (Count = 0; Count < BUFFER_SIZE; Count++) {
		WriteBuffer[Count] = (u8)(Count + Test);
		ReadBuffer[Count] = 0;
	}


	/*
	 * Transmit the data.
	 */
	XSpi_Transfer(SpiInstancePtr, WriteBuffer, ReadBuffer, BUFFER_SIZE);

	/*
	 * Compare the data received with the data that was transmitted.
	 */
	for (Count = 0; Count < BUFFER_SIZE; Count++) {
		if (WriteBuffer[Count] != ReadBuffer[Count]) {
			return XST_FAILURE;
		}
	}

	return XST_SUCCESS;
}
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编译下载之后，串口提示运行成功，

将loopback模式关闭，设置为禁止loopback，CPOL = 1 CPHA = 1。

Status = XSpi_SetOptions(SpiInstancePtr, XSP_MASTER_OPTION |
 					XSP_LOOPBACK_OPTION);
//修改为禁止loopback，CPOL = 1 CPHA = 1
Status = XSpi_SetOptions(SpiInstancePtr, XSP_MASTER_OPTION |
 					XSP_CLK_PHASE_1_OPTION | XSP_CLK_ACTIVE_LOW_OPTION);
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然后，把mosi引脚和miso引脚短接。然后编译、下载，提示运行错误

使用示波器测量SCK、mosi引脚，发现没有波形。

原因分析：

然后在Xilinx的论坛上发现也有人反馈这个问题，最后原因好像是：
因为SS0的引脚一直输出是高电平引起的，我后来将程序修改为持续向SPI发送数据，发现确实是SS0引脚一直是高电平（刚烧写完程序，SS0也会持续一段时间的高电平）。
个人认为可能是SPI自动选择从机编号发生了问题。

解决方案：

参考论坛中的解决方法，具体解决方案：
将从机选择设置为手动选择(XSP_MANUAL_SSELECT_OPTION)

Status = XSpi_SetOptions(SpiInstancePtr, XSP_MASTER_OPTION |
			 XSP_CLK_PHASE_1_OPTION | XSP_CLK_ACTIVE_LOW_OPTION | XSP_MANUAL_SSELECT_OPTION);
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然后再在SPI禁止中断语句之后，加入选择从机编号的语句。（1号从机的选择引脚就是SS0）

    /*
	 * Disable Global interrupt to use polled mode operation
	 */
	XSpi_IntrGlobalDisable(SpiInstancePtr);
	XSpi_SetSlaveSelect(SpiInstancePtr, 0x01);  //选择从机编号
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经过以上修改后，再次编译烧写，程序运行正确。