usb urb

line has its own story. In this section, we will only talk about one line of code. Yes, it is a line of code, because we need to introduce a term, a well-known name, which is the legendary "urb ", USB RequestBlock. The USB device needs to communicate with each other. to transmit data, you need to use urb. Specifically

1. URB Structural BodyUSB Request block (USB requestor block,urb) is a USB device driver used to describe the basic carrier and core data structure for communication with USB devices, very similar to the SK_BUFF structure in network device drivers. struct

Usb_alloc_urb Usb_free_urb Allocate and release Urb filling:Specify the urb type, which can be Ctrl, bulk, Int, or ISO.Enter the callback function. Usb_submit_urbUsb_unlink_urbFill the urb structure or remove it from the USB system. When the urb type is ISO or Int, an

It indicates that any short read that may occur on an in endpoint should be treated as an error by the USB core. this value is only useful for reading urb from a USB device, not for writing URBS. Urb_iso_asapIf this urb is synchronized, this bit can be set. If the driver wants this

USB urb (USB request block) Kernel 2.6.29.4The USB device driver code communicates with all USB devices through urb. Urb uses the struct urb

for each configuration　　unsigned short bus_ma; Bus current available for use U8 Portnum; Parent port numberU8 level; Number of layers in the USB hub　　unsigned can_submit:1; URB can be submitted flagunsigned discon_suspended:1; Break flag when pausedunsigned persist_enabled:1; Usb_persist Enable flagunsigned have_langid:1; String_langid Presence Flagunsigned authorized:1;unsigned authenticated:1;unsigned wu

]; // The Sub-device connected to the hub.Int pm_usage_cnt; // use count for automatic suspensionU32 quirks;Atomic_t urbnum; // The urb count submitted by this device　　Unsigned long active_duration; // use timing after activation # Ifdef config_pm // related to power managementStruct delayed_work autosuspend; // automatic suspension DelayStruct work_struct autoresume; // (interrupted) Automatic wake-up requestStruct mutex pm_mutex; // The mutex of the

1. Environment:Upper machine: ubuntu16.04Linux Jello 4.4.0-89-generic #112-ubuntu SMP Mon Jul 19:38:41 UTC x86_64 x86_64 x86_64 gnu/linuxLower machine:/home/jello # Uname-aLinux 3.10.0 #2 SMP Mon Mar 6 17:52:09 CST armv7l gnu/linux2. Background:The host computer through the USB to the serial port to connect the lower machine, uses the Kermit carries on the serial port interaction, suddenly in the upper computer cannot interact, the serial port does no

kernel version, the same as below)/drivers/usb, file name is usb-skeleton.c. Write a USB driver mostThere are four things to do: the device to be supported by the driver, the USB driver to be registered, the detection and disconnection, the submission and control of urb (

complete the communication.The so-called function driver is what this USB device is for, such as a USB camera, or a USB keyboard.function driven on the bus driver above, the USB interface protocol is a standard common protocol, generally with USB interface devices, the unde

guarantee that the transmission is completed within a specific time range. If there is not enough space on the bus to send the entire BULK package, it is divided into multiple packages for transmission. These endpoints are generally used on printers, USB Mass Storage, and USB network devices.4) When ISOCHRONOUS is used, the endpoint also transfers a large amount of data in batches, but this data cannot be

);Usb_set_intfdata (interface, null );Usb_deregister_dev (interface, skel_class );Then, he will use kref_put ( Dev-> kref, skel_delete) to clean up. For details about kref_put, refer to the previous article.So far, we have analyzed the main operations required by the USB subsystem. The next section will discuss the I/O operations on the USB device.When talking about the I/O operation of the

Previous article: http://www.2cto.com/ OS /201511/114321.htmlin usb_stor_bulk_transport (), the first most important function called in this function is usb_stor_bulk_transfer_buf (). Still from drivers/usb/stroage/transport. c: previous: http://www.2cto.com/ OS /201112/114321.html In usb_stor_Bulk_transport (), the first most important function called in this function is usb_stor_bulk_transfer_buf (). Still from drivers/

;//Descriptor Type _ _le16 wdata [1]; /* encoded with Utf-16le */ 2 USB Host Drive　　USB host controllers are available in 3 sizes: OHCI (Open Host controller Interface), UHCI (Universal hosts controller Interface) and EHCI (Enhanced host Co Ntroller Interface).2.1 Host Controller DriverIn the Linux kernel, the USB_HCD structure is used to describe the U