Table of Contents
What is Linux USB gadget?
In the Linux kernel an implementation of a USB device is called a USB gadget. This implementation of gadgets is nicely layered: there is a so called composite layer, which contains code common for all USB functionalities and allows composing gadgets out of several functionalities.
What is UDC Linux?
A USB Linux Gadget is a device which has a UDC (USB Device Controller) and can be connected to a USB Host to extend it with additional functions like a serial port or a mass storage capability.
What types of USB devices does Linux support?
Linux currently supports almost all USB class devices (standard types of devices like keyboards, mice, modems, printers and speakers) and an ever-growing number of vendor-specific devices (such as USB to serial converters, digital cameras, Ethernet devices and MP3 players).
What is USB device mode?
Device mode makes it possible for the computer to present itself as different kinds of USB device classes, including serial ports, network adapters, and mass storage, or a combination thereof. A USB host like a laptop or desktop computer is able to access them just like physical USB devices.
What is Configfs in Linux?
Configfs is for creating, managing and destroying kernel objects from user-space, and sysfs for viewing and manipulating objects from user-space which are created and destroyed by kernel space. It is typically mounted at /sys/kernel/config (or more rarely at /config ).
What is USB controller?
USB host controller has all USB state machine to handle USB devices, enumeration process, ID, etc .. USB device controller has state machine to device enumerate at host at your specific class like mass storage, HID, vendor specific.
How does Linux handle USB devices?
The Linux kernel supports two main types of USB drivers: drivers on a host system and drivers on a device. The USB drivers for a host system control the USB devices that are plugged into it, from the host’s point of view (a common USB host is a desktop computer.)
What is USB gadget driver?
The kernel module for the DT7816 USB gadget driver is a simplified version of gadgetfs and has the same kind of functionality. When loaded, it enumerates as a USB gadget, creates a specified number of bulk USB endpoints, and exposes each end point as a virtual file in the /dev directory.
What is an OTG device?
The on-the-go (OTG) cable is your ticket to connecting USB to your Android device. The OTG Cable At-a-Glance: OTG simply stands for ‘on the go’ OTG allows the connection of input devices, data storage, and A/V devices. OTG can allow you to connect up your USB mic to your Android phone.
What is raspberry gadget mode?
With “gadget mode” enabled, we don’t need to configure the WiFi network or connect any peripheral devices, we simply connect the Pi to our computer with a USB cable, and now we’ve got SSH access.
What is a USB Gadget in Linux?
In the Linux kernel an implementation of a USB device is called a USB gadget. This implementation of gadgets is nicely layered: there is a so called composite layer, which contains code common for all USB functionalities and allows composing gadgets out of several functionalities. The composite layer talks to the UDC driver.
What is the multifunction composite Gadget (G_multi)?
The Multifunction Composite Gadget (or g_multi) is a composite gadget that makes extensive use of the composite framework to provide a… multifunction gadget. In it’s standard configuration it provides a single USB configuration with RNDIS [1] (that is Ethernet), USB CDC [2] ACM (that is serial) and USB Mass Storage functions.
How are gadgets implemented in the USB interface?
This implementation of gadgets is nicely layered: there is a so called composite layer, which contains code common for all USB functionalities and allows composing gadgets out of several functionalities. The composite layer talks to the UDC driver.
What is the composite layer in a USB device?
The composite layer talks to the UDC driver. On top of the composite driver there are USB functionalities (such as mass storage or Ethernet), which are called USB functions. We will be focusing on the composite layer and functions. The traditional approach to gadgets composition was to create a kernel module for a given composition of a gadget.