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<!-- Copyright (C) 2002 Red Hat, Inc. -->
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<!-- permission is obtained from the copyright holder. -->
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<HTML
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><HEAD
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><TITLE
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>Introduction</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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"><LINK
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REL="HOME"
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TITLE="eCos USB Slave Support"
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HREF="io-usb-slave.html"><LINK
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REL="PREVIOUS"
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TITLE="eCos USB Slave Support"
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HREF="io-usb-slave.html"><LINK
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REL="NEXT"
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TITLE="USB Enumeration Data"
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HREF="usbs-enum.html"></HEAD
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><TH
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COLSPAN="3"
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>eCos USB Slave Support</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="io-usb-slave.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="usbs-enum.html"
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>Next</A
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></TD
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></TR
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></TABLE
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="USBS-INTRO"
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>Introduction</A
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN6"
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></A
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><H2
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>Name</H2
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>Introduction -- eCos support for USB slave devices</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN9"
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></A
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><H2
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>Introduction</H2
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><P
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>The eCos USB slave support allows developers to produce USB
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peripherals. It consists of a number of different eCos packages:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Device drivers for specific implementations of USB slave hardware, for
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example the on-chip USB Device Controller provided by the Intel SA1110
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processor. A typical USB peripheral will only provide one USB slave
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port and therefore only one such device driver package will be needed.
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Usually the device driver package will be loaded automatically when
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you create an eCos configuration for target hardware that has a USB
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slave device. If you select a target which does have a USB slave
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device but no USB device driver is loaded, this implies that no such
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device driver is currently available.</P
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></LI
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><LI
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><P
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>The common USB slave package. This serves two purposes. It defines the
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API that specific device drivers should implement. It also provides
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various utilities that will be needed by most USB device drivers and
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applications, such as handlers for standard control messages.
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Usually this package will be loaded automatically at the same time as
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the USB device driver.</P
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></LI
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><LI
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><P
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>The common USB package. This merely provides some information common
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to both the host and slave sides of USB, such as details of the
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control protocol. It is also used to place the other USB-related
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packages appropriately in the overall configuration hierarchy. Usually
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this package will be loaded at the same time as the USB device driver.</P
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></LI
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><LI
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><P
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>Class-specific USB support packages. These make it easier to develop
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specific classes of USB peripheral, such as a USB-ethernet device. If
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no suitable package is available for a given class of peripheral then
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the USB device driver can instead be accessed directly from
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application code. Such packages will never be loaded automatically
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since the configuration system has no way of knowing what class of USB
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peripheral is being developed. Instead developers have to add the
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appropriate package or packages explicitly.</P
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></LI
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></OL
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><P
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>These packages only provide support for developing USB peripherals,
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not USB hosts.</P
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN22"
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></A
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><H2
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>USB Concepts</H2
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><P
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>Information about USB can be obtained from a number of sources
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including the <A
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HREF="http://www.usb.org/"
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TARGET="_top"
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>USB Implementers Forum
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web site</A
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>. Only a brief summary is provided here.</P
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><P
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>A USB network is asymmetrical: it consists of a single host, one or
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more slave devices, and possibly some number of intermediate hubs. The
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host side is significantly more complicated than the slave side.
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Essentially, all operations are initiated by the host. For example, if
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the host needs to receive some data from a particular USB peripheral
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then it will send an IN token to that peripheral; the latter should
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respond with either a NAK or with appropriate data. Similarly, when
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the host wants to transmit data to a peripheral it will send an OUT
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token followed by the data; the peripheral will return a NAK if it is
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currently unable to receive more data or if there was corruption,
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otherwise it will return an ACK. All transfers are check-summed and
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there is a clearly-defined error recovery process. USB peripherals can
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only interact with the host, not with each other.</P
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><P
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>USB supports four different types of communication: control messages,
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interrupt transfers, isochronous transfers, and bulk transfers.
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Control messages are further subdivided into four categories:
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standard, class, vendor and a reserved category. All USB peripherals
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must respond to certain standard control messages, and usually this
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will be handled by the common USB slave package (for complicated
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peripherals, application support will be needed). Class and vendor
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control messages may be handled by an class-specific USB support
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package, for example the USB-ethernet package will handle control
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messages such as getting the MAC address or enabling/disabling
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promiscuous mode. Alternatively, some or all of these messages will
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have to be handled by application code.</P
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><P
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>Interrupt transfers are used for devices which need to be polled
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regularly. For example, a USB keyboard might be polled once every
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millisecond. The host will not poll the device more frequently than
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this, so interrupt transfers are best suited to peripherals that
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involve a relatively small amount of data. Isochronous transfers are
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intended for multimedia-related peripherals where typically a large
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amount of video or audio data needs to be exchanged continuously.
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Given appropriate host support a USB peripheral can reserve some of
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the available bandwidth. Isochronous transfers are not reliable; if a
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particular packet is corrupted then it will just be discarded and
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software is expected to recover from this. Bulk transfers are used for
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everything else: after taking care of any pending control, isochronous
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and interrupt transfers the host will use whatever bandwidth remains
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for bulk transfers. Bulk transfers are reliable.</P
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><P
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>Transfers are organized into USB packets, with the details depending
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on the transfer type. Control messages always involve an initial
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8-byte packet from host to peripheral, optionally followed by some
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additional packets; in theory these additional packets can be up to 64
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bytes, but hardware may limit it to 8 bytes. Interrupt transfers
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involve a single packet of up to 64 bytes. Isochronous transfers
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involve a single packet of up to 1024 bytes. Bulk transfers involve
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multiple packets. There will be some number, possibly zero, of 64-byte
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packets. The transfer is terminated by a single packet of less than 64
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bytes. If the transfer involves an exact multiple of 64 bytes than the
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final packet will be 0 bytes, consisting of just a header and checksum
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which typically will be generated by the hardware. There is no
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pre-defined limit on the size of a bulk transfer. Instead higher-level
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protocols are expected to handle this, so for a USB-ethernet
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peripheral the protocol could impose a limit of 1514 bytes of data
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plus maybe some additional protocol overhead.</P
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><P
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>Transfers from the host to a peripheral are addressed not just to that
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peripheral but to a specific endpoint within that peripheral.
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Similarly, the host requests incoming data from a specific endpoint
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rather than from the peripheral as a whole. For example, a combined
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keyboard/touchpad device could provide the keyboard events on endpoint
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1 and the mouse events on endpoint 2. A given USB peripheral can have
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up to 16 endpoints for incoming data and another 16 for outgoing data.
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However, given the comparatively high speed of USB I/O this endpoint
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addressing is typically implemented in hardware rather than software,
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and the hardware will only implement a small number of endpoints.
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Endpoint 0 is generally used only for control messages.</P
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><P
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>In practice, many of these details are irrelevant to application code
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or to class packages. Instead, such higher-level code usually just
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performs blocking <TT
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CLASS="FUNCTION"
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>read</TT
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> and
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<TT
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CLASS="FUNCTION"
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>write</TT
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>, or non-blocking USB-specific calls, to
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transfer data between host and target via a specific endpoint. Control
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messages are more complicated but are usually handled by existing
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code.</P
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><P
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>When a USB peripheral is plugged into the host there is an initial
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enumeration and configuration process. The peripheral provides
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information such as its class of device (audio, video, etc.), a
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vendor id, which endpoints should be used for what kind of data, and
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so on. The host OS uses this information to identify a suitable host
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device driver. This could be a generic driver for a class of
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peripherals, or it could be a vendor-specific driver. Assuming a
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suitable driver is installed the host will then activate the USB
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peripheral and perform additional application-specific initialisation.
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For example for a USB-ethernet device this would involve obtaining an
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ethernet MAC address. Most USB peripherals will be fairly simple, but
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it is possible to build multifunction peripherals with multiple
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configurations, interfaces, and alternate interface settings.</P
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><P
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>It is not possible for any of the eCos packages to generate all the
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enumeration data automatically. Some of the required information such
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as the vendor id cannot be supplied by generic packages; only by the
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application developer. Class support code such as the USB-ethernet
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package could in theory supply some of the information automatically,
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but there are also hardware dependencies such as which endpoints get
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| 270 |
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used for incoming and outgoing ethernet frames. Instead it is the
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responsibility of the application developer to provide all the
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| 272 |
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enumeration data and perform some additional initialisation. In
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addition, the common USB slave package can handle all the standard
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control messages for a simple USB peripheral, but for something like a
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multifunction peripheral additional application support is needed.</P
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| 276 |
|
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><DIV
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CLASS="NOTE"
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><BLOCKQUOTE
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CLASS="NOTE"
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><P
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| 281 |
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><B
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>Note: </B
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| 283 |
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>The initial implementation of the eCos USB slave packages involved
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| 284 |
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hardware that only supported control and bulk transfers, not
|
| 285 |
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isochronous or interrupt. There may be future changes to the USB
|
| 286 |
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code and API to allow for isochronous and interrupt transfers,
|
| 287 |
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|
especially the former. Other changes may be required to support
|
| 288 |
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different USB devices. At present there is no support for USB remote
|
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wakeups, since again it is not supported by the hardware.</P
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></BLOCKQUOTE
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></DIV
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN38"
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></A
|
| 298 |
|
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><H2
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| 299 |
|
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>eCos USB I/O Facilities</H2
|
| 300 |
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|
><P
|
| 301 |
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>For protocols other than control messages, eCos provides two ways of
|
| 302 |
|
|
performing USB I/O. The first involves device table or devtab entries such
|
| 303 |
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as <A
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| 304 |
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HREF="usbs-devtab.html"
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><TT
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CLASS="LITERAL"
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>/dev/usb1r</TT
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></A
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>,
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with one entry per endpoint per USB device. It is possible to
|
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<TT
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| 312 |
|
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CLASS="FUNCTION"
|
| 313 |
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>open</TT
|
| 314 |
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> these devices and use conventional blocking
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| 315 |
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I/O functions such as <TT
|
| 316 |
|
|
CLASS="FUNCTION"
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| 317 |
|
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>read</TT
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| 318 |
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|
> and
|
| 319 |
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<TT
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| 320 |
|
|
CLASS="FUNCTION"
|
| 321 |
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>write</TT
|
| 322 |
|
|
> to exchange data between host and
|
| 323 |
|
|
peripheral.</P
|
| 324 |
|
|
><P
|
| 325 |
|
|
>There is also a lower-level USB-specific API, consisting of functions
|
| 326 |
|
|
such as <A
|
| 327 |
|
|
HREF="usbs-start-rx.html"
|
| 328 |
|
|
><TT
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| 329 |
|
|
CLASS="FUNCTION"
|
| 330 |
|
|
>usbs_start_rx_buffer</TT
|
| 331 |
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></A
|
| 332 |
|
|
>.
|
| 333 |
|
|
A USB device driver will supply a data structure for each endpoint,
|
| 334 |
|
|
for example a <A
|
| 335 |
|
|
HREF="usbs-data.html"
|
| 336 |
|
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><SPAN
|
| 337 |
|
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CLASS="STRUCTNAME"
|
| 338 |
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>usbs_rx_endpoint</SPAN
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| 339 |
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></A
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| 340 |
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>
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| 341 |
|
|
structure for every receive endpoint. The first argument to
|
| 342 |
|
|
<TT
|
| 343 |
|
|
CLASS="FUNCTION"
|
| 344 |
|
|
>usbs_start_rx_buffer</TT
|
| 345 |
|
|
> should be a pointer to such
|
| 346 |
|
|
a data structure. The USB-specific API is non-blocking: the initial
|
| 347 |
|
|
call merely starts the transfer; some time later, once the transfer
|
| 348 |
|
|
has completed or has been aborted, the device driver will invoke a
|
| 349 |
|
|
completion function.</P
|
| 350 |
|
|
><P
|
| 351 |
|
|
>Control messages are different. With four different categories of
|
| 352 |
|
|
control messages including application and vendor specific ones, the
|
| 353 |
|
|
conventional
|
| 354 |
|
|
<TT
|
| 355 |
|
|
CLASS="FUNCTION"
|
| 356 |
|
|
>open</TT
|
| 357 |
|
|
>/<TT
|
| 358 |
|
|
CLASS="FUNCTION"
|
| 359 |
|
|
>read</TT
|
| 360 |
|
|
>/<TT
|
| 361 |
|
|
CLASS="FUNCTION"
|
| 362 |
|
|
>write</TT
|
| 363 |
|
|
>
|
| 364 |
|
|
model of I/O cannot easily be applied. Instead, a USB device driver
|
| 365 |
|
|
will supply a <A
|
| 366 |
|
|
HREF="usbs-control.html"
|
| 367 |
|
|
><SPAN
|
| 368 |
|
|
CLASS="STRUCTNAME"
|
| 369 |
|
|
>usbs_control_endpoint</SPAN
|
| 370 |
|
|
></A
|
| 371 |
|
|
>
|
| 372 |
|
|
data structure which can be manipulated appropriately. In practice the
|
| 373 |
|
|
standard control messages will usually be handled by the common USB
|
| 374 |
|
|
slave package, and other control messages will be handled by
|
| 375 |
|
|
class-specific code such as the USB-ethernet package. Typically,
|
| 376 |
|
|
application code remains responsible for supplying the <A
|
| 377 |
|
|
HREF="usbs-enum.html"
|
| 378 |
|
|
>enumeration data</A
|
| 379 |
|
|
> and for actually <A
|
| 380 |
|
|
HREF="usbs-start.html"
|
| 381 |
|
|
>starting</A
|
| 382 |
|
|
> up the USB device.</P
|
| 383 |
|
|
></DIV
|
| 384 |
|
|
><DIV
|
| 385 |
|
|
CLASS="REFSECT1"
|
| 386 |
|
|
><A
|
| 387 |
|
|
NAME="AEN60"
|
| 388 |
|
|
></A
|
| 389 |
|
|
><H2
|
| 390 |
|
|
>Enabling the USB code</H2
|
| 391 |
|
|
><P
|
| 392 |
|
|
>If the target hardware contains a USB slave device then the
|
| 393 |
|
|
appropriate USB device driver and the common packages will typically
|
| 394 |
|
|
be loaded into the configuration automatically when that target is
|
| 395 |
|
|
selected (assuming a suitable device driver exists). However, the
|
| 396 |
|
|
driver will not necessarily be active. For example a processor might
|
| 397 |
|
|
have an on-chip USB device, but not all applications using that
|
| 398 |
|
|
processor will want to use USB functionality. Hence by default the USB
|
| 399 |
|
|
device is disabled, ensuring that applications do not suffer any
|
| 400 |
|
|
memory or other penalties for functionality that is not required.</P
|
| 401 |
|
|
><P
|
| 402 |
|
|
>If the application developer explicitly adds a class support package
|
| 403 |
|
|
such as the USB-ethernet one then this implies that the USB device is
|
| 404 |
|
|
actually needed, and the device will be enabled automatically.
|
| 405 |
|
|
However, if no suitable class package is available and the USB device
|
| 406 |
|
|
will instead be accessed by application code, it is necessary to
|
| 407 |
|
|
enable the USB device manually. Usually the easiest way to do this is
|
| 408 |
|
|
to enable the configuration option
|
| 409 |
|
|
<TT
|
| 410 |
|
|
CLASS="LITERAL"
|
| 411 |
|
|
>CYGGLO_IO_USB_SLAVE_APPLICATION</TT
|
| 412 |
|
|
>, and the USB device
|
| 413 |
|
|
driver and related packages will adjust accordingly. Alternatively,
|
| 414 |
|
|
the device driver may provide some configuration options to provide
|
| 415 |
|
|
more fine-grained control.</P
|
| 416 |
|
|
></DIV
|
| 417 |
|
|
><DIV
|
| 418 |
|
|
CLASS="NAVFOOTER"
|
| 419 |
|
|
><HR
|
| 420 |
|
|
ALIGN="LEFT"
|
| 421 |
|
|
WIDTH="100%"><TABLE
|
| 422 |
|
|
WIDTH="100%"
|
| 423 |
|
|
BORDER="0"
|
| 424 |
|
|
CELLPADDING="0"
|
| 425 |
|
|
CELLSPACING="0"
|
| 426 |
|
|
><TR
|
| 427 |
|
|
><TD
|
| 428 |
|
|
WIDTH="33%"
|
| 429 |
|
|
ALIGN="left"
|
| 430 |
|
|
VALIGN="top"
|
| 431 |
|
|
><A
|
| 432 |
|
|
HREF="io-usb-slave.html"
|
| 433 |
|
|
>Prev</A
|
| 434 |
|
|
></TD
|
| 435 |
|
|
><TD
|
| 436 |
|
|
WIDTH="34%"
|
| 437 |
|
|
ALIGN="center"
|
| 438 |
|
|
VALIGN="top"
|
| 439 |
|
|
><A
|
| 440 |
|
|
HREF="io-usb-slave.html"
|
| 441 |
|
|
>Home</A
|
| 442 |
|
|
></TD
|
| 443 |
|
|
><TD
|
| 444 |
|
|
WIDTH="33%"
|
| 445 |
|
|
ALIGN="right"
|
| 446 |
|
|
VALIGN="top"
|
| 447 |
|
|
><A
|
| 448 |
|
|
HREF="usbs-enum.html"
|
| 449 |
|
|
>Next</A
|
| 450 |
|
|
></TD
|
| 451 |
|
|
></TR
|
| 452 |
|
|
><TR
|
| 453 |
|
|
><TD
|
| 454 |
|
|
WIDTH="33%"
|
| 455 |
|
|
ALIGN="left"
|
| 456 |
|
|
VALIGN="top"
|
| 457 |
|
|
>eCos USB Slave Support</TD
|
| 458 |
|
|
><TD
|
| 459 |
|
|
WIDTH="34%"
|
| 460 |
|
|
ALIGN="center"
|
| 461 |
|
|
VALIGN="top"
|
| 462 |
|
|
> </TD
|
| 463 |
|
|
><TD
|
| 464 |
|
|
WIDTH="33%"
|
| 465 |
|
|
ALIGN="right"
|
| 466 |
|
|
VALIGN="top"
|
| 467 |
|
|
>USB Enumeration Data</TD
|
| 468 |
|
|
></TR
|
| 469 |
|
|
></TABLE
|
| 470 |
|
|
></DIV
|
| 471 |
|
|
></BODY
|
| 472 |
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></HTML
|
| 473 |
|
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>
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