(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)