AM335x USB Driver's Guide

= Quick Start Guide = This section is a quick guide on how to start using usb ports on TI platform with supplied pre-built binaries. Please refer to USB Quick Start

= Introduction = The USB User's Guide provides information about
 * Overview of USB hardware and software
 * Supported linux driver features for USB host and device mode of operation
 * The Linux USB configuration through menuconfig. Please refer to USB configuration

=  Hardware Overview  =

USBSS Overview

 * The USB subsystem includes
 * Two instances of USB (Mentor Graphic's USB2.0 OTG) controllers. Each MUSB controller supports USB 1.1 and USB 2.0 standard.
 * CPPI 4.1 compliant DMA controller sub-module with 30 RX and 30 TX simultaneous DMA channels
 * CPPI 4.1 DMA scheduler
 * CPPI Queue Manager module with 92 queues for queuing/dequeuing packets


 * Interfaces to the CPU via 3 OCP interfaces
 * Master OCP HP interface for the DMA (for data transfers)
 * Master OCP HP interface for the Queue manager (to manage CPPI descriptors)
 * Slave OCP MMR interface (for CPU to access USBSS/MUSB registers)


 * Signals the standard Charge Pump (part of EVM BOM) for VBUS 5V generation

MUSB Controller Overview
The salient features of the MUSB USB2.0 OTG controller are:


 * High/full speed operation as USB peripheral.
 * High/full/low speed operation as Host controller.
 * Compliant with OTG spec.
 * 15 Transmit and 15 Receive Endpoints other than the mandatory Control Endpoint 0.
 * Double buffering support in FIFO.
 * Support for high bandwidth Isochronous transfer
 * 32 Kilobytes of Endpoint FIFO RAM for USB packet buffering.
 * Interfaced with CPPI4.1 DMA controller with 15 Rx and 15 Tx channels (for each usb controller).
 * Defer interrupt enable feature is supported for each packet descriptor of cppi-dma.

=  Software Overview  =

Mentor graphics controller driver (or MUSB driver)
The MUSB driver is implemented on top of Mentor controller IP which supports all the speeds (High, Full and Low). AM33XX USBOTG subsytem uses CPPI 4.1 DMA for all the transfers. The musb driver conforms to linux usb framework and supports both PIO and DMA mode of operation. The musb host controller driver (HCD) binds the controller hardware to linux usb core stack. The musb device or gadget controller driver binds the controller hardware and specific gadget driver (filestorage, cdc/rndis etc).

Linux USB Stack Architecture
As shown in the figure, linux usb stack is a layered architecture, with musb controller at the lowest layer, the musb host/device controller driver binds the musb controller hardware to linux usb stack framework. The CPPI4.1 DMA controller driver is responsible for transmit/receive of packets over the musb endpoints.



= Driver Features List =
 * The Mentor USB driver can be built as module or built-in to kernel
 * Support both PIO and DMA mode (The DMA mode not applicable for control endpoint)
 * Support two instances musb controller in otg mode (both usb0 and usb1 controller in otg mode. This will allow host or device operation on each port simultaneously.

Not verified features of AM33xx
= References =
 * For more details about EVM, please refer to EVM reference manual.

USB Configuration through menuconfig

 * The Mentor USB driver can be built as module or built into kernel. For more information refer to USB Configuration