標題: 关于Urb的一些基础认识 [打印本頁] 作者: lcmj44444444 時間: 2013-1-5 20:29 標題: 关于Urb的一些基础认识 在内核中的USB代码和USB设备进行通信，使用的是Urb(USB request block)。Urb可以看成是一个USB的驱动和USB 的endpoint通信的桥梁。有两种方式
Urb的定义如下
struct urb
{
/* private, usb core and host controller only fields in the urb */
struct kref kref; /* reference count of the URB */
spinlock_t lock; /* lock for the URB */
void *hcpriv; /* private data for host controller */
struct list_head urb_list; /* list pointer to all active urbs */
int bandwidth; /* bandwidth for INT/ISO request */
atomic_t use_count; /* concurrent submissions counter */
u8 reject; /* submissions will fail */
/* public, documented fields in the urb that can be used by drivers */
struct usb_device *dev; /* (in) pointer to associated device */
unsigned int pipe; /* (in) pipe information */
int status; /* (return) non-ISO status */
unsigned int transfer_flags; /* (in) URB_SHORT_NOT_OK | ...*/
void *transfer_buffer; /* (in) associated data buffer */
dma_addr_t transfer_dma; /* (in) dma addr for transfer_buffer */
int transfer_buffer_length; /* (in) data buffer length */
int actual_length; /* (return) actual transfer length */
unsigned char *setup_packet; /* (in) setup packet (control only) */
dma_addr_t setup_dma; /* (in) dma addr for setup_packet */
int start_frame; /* (modify) start frame (ISO) */
int number_of_packets; /* (in) number of ISO packets */
int interval; /* (modify) transfer interval (INT/ISO) */
int error_count; /* (return) number of ISO errors */
void *context; /* (in) context for completion */
usb_complete_t complete; /* (in) completion routine */
struct usb_iso_packet_descriptor iso_frame_desc[0]; /* (in) ISO ONLY */
};
一个Urb的生命周期
1、 USB 设备驱动创建Urb
为了不破坏USB core中Urb的引用计数器，Urb不能静态创建。或者在另一个结构中。只能通过对usb_alloc_urb的调用来创建。函数原型为：
struct urb *usb_alloc_urb(int iso_packets, int mem_flags);
2、 分配一个Endpoint,由于Endpoint有四种类型，所以在分配的时候也有4个方法：
Interrupt EndPoint
void usb_fill_int_urb(struct urb *urb, struct usb_device *dev, unsigned int pipe, void *transfer_buffer, int buffer_length, usb_complete_t complete, void *context, int interval);
Bulk EndPoint
void usb_fill_bulk_urb(struct urb *urb, struct usb_device *dev, unsigned int pipe, void *transfer_buffer, int buffer_length, usb_complete_t complete, void *context);
Control EndPoint
void usb_fill_control_urb(struct urb *urb, struct usb_device *dev, unsigned int pipe, unsigned char *setup_packet, void *transfer_buffer, int buffer_length, usb_complete_t complete, void *context);
