《Linux那些事儿之我是USB》我是U盘（12）从协议中来到协议中去(中)--总结

(1)

usb设备要遵循的就是usb协议. 不管是软件还是硬件,在设计的伊始,总是要参考usb协议.怎么设计硬件,如何编写软件,不看usb协议,谁也不可能凭空想象出来.

(2)

usb协议规定了,每个usb设备都得有些基本的元素,称为描述符,有四类描述符是任何一种usb设备都得有的.他们是,device descriptor,configuration descriptor,interface descriptor,endpoint descriptor.描述符里的冬冬是一个设备出厂的时候就被厂家给固化在设备里了.

关于这几种描述符,usb core在总线扫描那会就会去读取,会去获得里边的信息,其中,device描述符描述的是整个device.

对于usb设备驱动程序编写者来说,usb_interface和usb_endpoint更加重要.一个interface对应一个usb设备驱动程序.比如：一个usb设备,两种功能,一个键盘,上面带一个扬声器,两个接口,那这样肯定得要两个驱动程序,一个是键盘驱动程序,一个是音频流驱动程序.

struct usb_interface {

/* array of alternate settings for this interface,

* stored in no particular order */

struct usb_host_interface *altsetting;

struct usb_host_interface *cur_altsetting; /* the currently * active alternate setting */

unsigned num_altsetting; /* number of alternate settings */

/* If there is an interface association descriptor then it will list

* the associated interfaces */

struct usb_interface_assoc_descriptor *intf_assoc;

int minor; /* minor number this interface is

* bound to */

enum usb_interface_condition condition; /* state of binding */

unsigned sysfs_files_created:1; /* the sysfs attributes exist */

unsigned ep_devs_created:1; /* endpoint "devices" exist */

unsigned unregistering:1; /* unregistration is in progress */

unsigned needs_remote_wakeup:1; /* driver requires remote wakeup */

unsigned needs_altsetting0:1; /* switch to altsetting 0 is pending */

unsigned needs_binding:1; /* needs delayed unbind/rebind */

unsigned reset_running:1;

unsigned resetting_device:1; /* true: bandwidth alloc after reset */

struct device dev; /* interface specific device info */

struct device *usb_dev;

atomic_t pm_usage_cnt; /* usage counter for autosuspend */

struct work_struct reset_ws; /* for resets in atomic context */

};

#define to_usb_interface(d) container_of(d, struct usb_interface, dev)