USB Host Controller : UHCI OHCI EHCI
UHCI: intel low speed (1.5Mbps) (USB1.1) / full-speed (12Mbps) (USB2.0, USB2.0 is divided into full and high speed)
the OHCI: Microsoft: low / full
EHCI: high speed (480Mbps)
USB bus driver action :
1. Identify the USB device
1.1 allocate addresses
1.2 and tell the USB device (SET address)
1.3 issue a command descriptor obtaining
information descriptor can be seen in include \ linux \ usb \ ch9.h in
2. Find and install the device driver corresponding
3. The USB provides read and write functions
How the program is called, simply look at:
In the drivers / usb / core / hub.c file:
Each controller comes with a USB hub
hub_irq
kick_khubd
hub_thread
hub_events
hub_port_connect_change
choose_devnum to the new device // select a new number (address)
hub_port_init
hub_set_address // the number (address) told a USB device, the future will use this address.
usb_get_device_descriptor (udev, 8); // Get Device Descriptor
retval = usb_get_device_descriptor (the udev, USB_DT_DEVICE_SIZE);
usb_new_device (the udev)
// put the bus into the device dev list, remove the driver from the bus driver in the list, if it can match to call driver's Probe
device_add (& udev-> dev);
Note: This interrupt is registered inside the host controller interrupt, usb device is not interrupted. When connected to a USB device, the hardware makes hands D + or D- from low to high, the hardware on the perception of a USB device is connected, which will generate an interrupt. Thus there is a calling procedure above.
hub_port_connect_change
choose_devnum // select a new number (address) to the new device
/ * the Try the Next to the allocate at The Beginning BUS- DevNum, AT> devnum_next. * /
// Find Next 0, obviously an address with the corresponding inside address will be set to 1, indicating that the address is in use. From 1 128 to find, if not, you will find from scratch. Suppose the last time you plug in a USB device number, it devnum = 5, then it will start looking for from 5 to find after 128, if not found, it will find from the beginning. That is, after looking around, if not found, then come back. Can be seen from this place, a USB host controller can connect up to 128 USB devices.
devnum = find_next_zero_bit (bus-> devmap.devicemap, 128, bus-> devnum_next);
2, analysis of several important data structures
Device descriptor:
/* USB_DT_DEVICE: Device descriptor */
struct usb_device_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__le16 bcdUSB; //USB版本号
__u8 bDeviceClass;
__u8 bDeviceSubClass;
__u8 bDeviceProtocol;
__u8 bMaxPacketSize0; //最大包大小，0表示端点0.每个设备都有端点0，因为是通过端点0识别出USB设备的
__le16 idVendor; //厂家ID
__le16 idProduct; //产品ID
__le16 bcdDevice;
__u8 iManufacturer;
__u8 iProduct;
__u8 iSerialNumber;
__u8 bNumConfigurations;
} __attribute__ ((packed));
配置描述符：
struct usb_config_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__le16 wTotalLength;
__u8 bNumInterfaces;
__u8 bConfigurationValue;
__u8 iConfiguration;
__u8 bmAttributes;
__u8 bMaxPower;
} __attribute__ ((packed));
接口描述符：
/* USB_DT_INTERFACE: Interface descriptor */
struct usb_interface_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bInterfaceNumber;
__u8 bAlternateSetting;
__u8 bNumEndpoints;
__u8 bInterfaceClass;
__u8 bInterfaceSubClass;
__u8 bInterfaceProtocol;
__u8 iInterface;
} __attribute__ ((packed));
端点描述符
/* USB_DT_ENDPOINT: Endpoint descriptor */
struct usb_endpoint_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bEndpointAddress;
__u8 bmAttributes;
__le16 wMaxPacketSize; //从端点中一次写入或读出多少数据
__u8 bInterval;用查询的方式实现实时性的，此变量就表示查询的时间间隔。
/* NOTE: these two are _only_ in audio endpoints. */
/* use USB_DT_ENDPOINT*_SIZE in bLength, not sizeof. */
__u8 bRefresh;
__u8 bSynchAddress;
} __attribute__ ((packed));
它们的关系：
每一个USB设备，都有一个设备描述符，可以发出某些命令，得到USB设备描述符。一个硬件里面有一个设备描述符，
一个设备描述符里面还有配置描述符，一个设备描述符里面可能有多个配置描述符。
本节只是进行了简单的分析，并没有进行深入分析。