microblaze 串口学习·1

串口初始化函数1int XUartLite_Initialize(XUartLite *InstancePtr, u16 DeviceId)

/****************************************************************************/
/**
*
* Initialize a XUartLite instance.  The receive and transmit FIFOs of the
* UART are not flushed, so the user may want to flush them. The hardware
* device does not have any way to disable the receiver such that any valid
* data may be present in the receive FIFO. This function disables the UART
* interrupt. The baudrate and format of the data are fixed in the hardware
* at hardware build time.
*
* @param	InstancePtr is a pointer to the XUartLite instance.
* @param	DeviceId is the unique id of the device controlled by this
*		XUartLite instance.  Passing in a device id associates the
*		generic XUartLite instance to a specific device, as chosen by
*		the caller or application developer.
*
* @return
* 		- XST_SUCCESS if everything starts up as expected.
* 		- XST_DEVICE_NOT_FOUND if the device is not found in the
*			configuration table.
*
* @note		None.
*
*****************************************************************************/
int XUartLite_Initialize(XUartLite *InstancePtr, u16 DeviceId)
{
	XUartLite_Config *ConfigPtr;

	/*
	 * Assert validates the input arguments
	 */
	Xil_AssertNonvoid(InstancePtr != NULL);

	/*
	 * Lookup the device configuration in the configuration table. Use this
	 * configuration info when initializing this component.
	 */
	ConfigPtr = XUartLite_LookupConfig(DeviceId);

	if (ConfigPtr == (XUartLite_Config *)NULL) {
		return XST_DEVICE_NOT_FOUND;
	}
	return XUartLite_CfgInitialize(InstancePtr, ConfigPtr,
					ConfigPtr->RegBaseAddr);
}

#1 串口初始化函数的参数1 名为XUartLite的结构体指针

/**
 * The XUartLite driver instance data. The user is required to allocate a
 * variable of this type for every UART Lite device in the system. A pointer
 * to a variable of this type is then passed to the driver API functions.
 */
typedef struct {
	XUartLite_Stats Stats;			/* Component Statistics */
	UINTPTR RegBaseAddress;			/* Base address of registers */
	u32 IsReady;					/* Device is initialized and ready */

	XUartLite_Buffer SendBuffer;
	XUartLite_Buffer ReceiveBuffer;

	XUartLite_Handler RecvHandler;
	void *RecvCallBackRef;			/* Callback ref for recv handler */
	XUartLite_Handler SendHandler;
	void *SendCallBackRef;			/* Callback ref for send handler */
} XUartLite;

1-1 函数参数1 结构体指针 XUartLite_Stats Stats;

结构体元素1 外设状态信息
结构体种定义了外设的信息 由XUartLite_Stats定义的结构体

/**
 * Statistics for the XUartLite driver
 */
typedef struct {
	u32 TransmitInterrupts;		/**< Number of transmit interrupts */
	u32 ReceiveInterrupts;		/**< Number of receive interrupts */
	u32 CharactersTransmitted;	/**< Number of characters transmitted */
	u32 CharactersReceived;		/**< Number of characters received */
	u32 ReceiveOverrunErrors;	/**< Number of receive overruns */
	u32 ReceiveParityErrors;	/**< Number of receive parity errors */
	u32 ReceiveFramingErrors;	/**< Number of receive framing errors */
} XUartLite_Stats;

结构体种定义的全部为32bit的整形量,用于指示串口的状态太

1-2 结构体元素2 外设寄存器起始地址 UINTPTR RegBaseAddress;

UINTPTR为整形指针，指示的是外设寄存器的起始地址，这个起始地址可以在vivado的工程中查到

1-3 外设ready标志 device Ready u32 IsReady;

没用到以后再研究

1-4 输出缓冲堆结构体 XUartLite_Buffer SendBuffer;

/**
 * The following data type is used to manage the buffers that are handled
 * when sending and receiving data in the interrupt mode. It is intended
 * for internal use only.
 */
typedef struct {
	u8 *NextBytePtr;
	unsigned int RequestedBytes;
	unsigned int RemainingBytes;
} XUartLite_Buffer;

结构体种第一个元素是一个指针 指向u8的元素。本质上是一个地址。
第二个元素是请求数量，
第三个元素是未处理的请求数量

1-5 输入缓冲结构体 XUartLite_Buffer ReceiveBuffer;

/**
 * The following data type is used to manage the buffers that are handled
 * when sending and receiving data in the interrupt mode. It is intended
 * for internal use only.
 */
typedef struct {
	u8 *NextBytePtr;
	unsigned int RequestedBytes;
	unsigned int RemainingBytes;
} XUartLite_Buffer;

结构体种第一个元素是一个指针 指向u8的元素。本质上是一个地址。
第二个元素是请求数量，
第三个元素是未处理的请求数量

1-6 接收函数指针 XUartLite_Handler RecvHandler;

参数类型由以下typedef定义
这是一个返回值为空，有两个参数的函数的指针

typedef void (*XUartLite_Handler)(void *CallBackRef, unsigned int ByteCount);

第一个参数是一个空指针，看名字应该是指向回调函数，void是一个无类型的指针，可以被任何指针赋值

第二个参数是接收到的数据数量

1-7 接收回调函数void RecvCallBackRef; / Callback ref for recv handler */

一个无类型指针，应该是用于指向接收回调函数

1-8 发送函数指针 XUartLite_Handler SendHandler;

参数类型由以下typedef定义
这是一个返回值为空，有两个参数的函数的指针

typedef void (*XUartLite_Handler)(void *CallBackRef, unsigned int ByteCount);

第一个参数是一个空指针，看名字应该是指向回调函数，void是一个无类型的指针，可以被任何指针赋值

第二个参数是接收到的数据数量

1-9发送回调函数指针 void *SendCallBackRef;

一个无类型指针，应该是用于指向发送回调函数

2 串口初始化函数的参数2 第2个参数是外设ID

是一个16位的整形量，通常情况下是一个常数，这个常数由vivado生成外设硬件资源后，导出hardwareConfig时应该就已经确定了。
可以在vitis生成的工程中在xparameters.h文件种可以找到外设的ID
看文件的话这个ID就是看同类型的外设在总线上挂了多少个，如果外设都只有一个的话。目前生成的工程ID都是0，当由两个同类型外设的时候，才会出现不同的id。

3 总结

总结，在初始化的过程中，需要向初始化函数提供两个参数。

第一个参数有大量的功能性参数可供配置或查询，对于同类的外设来说，大家需要配置的参数类型都是一样的。
第二个参数实际上决定的是配置过程中的地址偏移，因为实际上所有的外设都是挂在AXI总线上执行的，对于CPU来说所有对于外设的操作都可以看作是对特定地址reg的读写操作。