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-><HR
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-><H1
-><A
-NAME="DEVS-USB-SA11X0">SA11X0 USB Device Driver</H1
-><DIV
-CLASS="REFNAMEDIV"
-><A
-NAME="AEN18754"
-></A
-><H2
->Name</H2
->SA11X0 USB Support -- Device driver for the on-chip SA11X0 USB device</DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN18757"
-></A
-><H2
->SA11X0 USB Hardware</H2
-><P
->The Intel StrongARM SA11x0 family of processors is supplied with an
-on-chip USB slave device, the UDC (USB Device Controller). This
-supports three endpoints. Endpoint 0 can only be used for control
-messages. Endpoint 1 can only be used for bulk transfers from host to
-peripheral. Endpoint 2 can only be used for bulk transfers from
-peripheral to host. Isochronous and interrupt transfers are not
-supported.</P
-><DIV
-CLASS="CAUTION"
-><P
-></P
-><TABLE
-CLASS="CAUTION"
-BORDER="1"
-WIDTH="100%"
-><TR
-><TD
-ALIGN="CENTER"
-><B
->Caution</B
-></TD
-></TR
-><TR
-><TD
-ALIGN="LEFT"
-><P
->Different revisions of the SA11x0 silicon have had various problems
-with the USB support. The device driver has been tested primarily
-against stepping B4 of the SA1110 processor, and may not function as
-expected with other revisions. Application developers should obtain
-the manufacturer's current errata sheets and specification updates.
-The B4 stepping still has a number of problems, but the device driver
-can work around these. However there is a penalty in terms of extra
-code, extra cpu cycles, and increased dispatch latency because extra
-processing is needed at DSR level. Interrupt latency should not be
-affected.</P
-><P
->There is one specific problem inherent in the UDC design of which
-application developers should be aware: the hardware cannot fully
-implement the USB standard for bulk transfers. A bulk transfer
-typically consists of some number of full-size 64-byte packets and is
-terminated by a packet less than the full size. If the amount of data
-transferred is an exact multiple of 64 bytes then this requires a
-terminating packet of 0 bytes of data (plus header and checksum). The
-SA11x0 USB hardware does not allow a 0-byte packet to be transmitted,
-so the device driver is forced to substitute a 1-byte packet and the
-host receives more data than expected. Protocol support is needed so
-that the appropriate host-side device driver can allow buffer space
-for the extra byte, detect when it gets sent, and discard it.
-Consequently certain standard USB class protocols cannot be
-implemented using the SA11x0, and therefore custom host-side device
-drivers will generally have to be provided, rather than re-using
-existing ones that understand the standard protocol.</P
-></TD
-></TR
-></TABLE
-></DIV
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN18763"
-></A
-><H2
->Endpoint Data Structures</H2
-><P
->The SA11x0 USB device driver can provide up to three data structures
-corresponding to the three endpoints: a
-<SPAN
-CLASS="STRUCTNAME"
->usbs_control_endpoint</SPAN
-> structure
-<TT
-CLASS="LITERAL"
->usbs_sa11x0_ep0</TT
->; a
-<SPAN
-CLASS="STRUCTNAME"
->usbs_rx_endpoint</SPAN
->
-<TT
-CLASS="LITERAL"
->usbs_sa11x0_ep1</TT
->; and a
-<SPAN
-CLASS="STRUCTNAME"
->usbs_tx_endpoint</SPAN
->
-<TT
-CLASS="LITERAL"
->usbs_sa11x0_ep2</TT
->. The header file
-<TT
-CLASS="FILENAME"
->cyg/io/usb/usbs_sa11x0.h</TT
->
-provides declarations for these.</P
-><P
->Not all applications will require support for all the endpoints. For
-example, if the intended use of the UDC only involves peripheral to
-host transfers then <TT
-CLASS="LITERAL"
->usbs_sa11x0_ep1</TT
-> is redundant.
-The device driver provides configuration options to control the
-presence of each endpoint:</P
-><P
-></P
-><OL
-TYPE="1"
-><LI
-><P
->Endpoint 0 is controlled by
-<TT
-CLASS="LITERAL"
->CYGFUN_DEVS_USB_SA11X0_EP0</TT
->. This defaults to
-enabled if there are any higher-level packages that require USB
-hardware or if the global preference
-<TT
-CLASS="LITERAL"
->CYGGLO_IO_USB_SLAVE_APPLICATION</TT
-> is enabled,
-otherwise it is disabled. Usually this has the desired effect. It may
-be necessary to override this in special circumstances, for example if
-the target board uses an external USB chip in preference to the UDC
-and it is that external chip's device driver that should be used
-rather than the on-chip UDC. It is not possible to disable endpoint 0
-and at the same time enable one or both of the other endpoints, since
-a USB device is only usable if it can process the standard control
-messages.</P
-></LI
-><LI
-><P
->Endpoint 1 is controlled by
-<TT
-CLASS="LITERAL"
->CYGPKG_DEVS_USB_SA11X0_EP1</TT
->. By default it is
-enabled whenever endpoint 0 is enabled, but it can be disabled
-manually when not required.</P
-></LI
-><LI
-><P
->Similarly endpoint 2 is controlled by
-<TT
-CLASS="LITERAL"
->CYGPKG_DEVS_USB_SA11X0_EP2</TT
->. This is also enabled by
-default whenever endpoint 0 is enabled, but it can be disabled manually.</P
-></LI
-></OL
-><P
->The SA11X0 USB device driver implements the interface specified by the
-common eCos USB Slave Support package. The documentation for that
-package should be consulted for further details. There is only one
-major deviation: when there is a peripheral to host transfer on
-endpoint 2 which is an exact multiple of the bulk transfer packet size
-(usually 64 bytes) the device driver has to pad the transfer with one
-extra byte. This is because of a hardware limitation: the UDC is
-incapable of transmitting 0-byte packets as required by the USB
-specification. Higher-level code, including the host-side device
-driver, needs to be aware of this and adapt accordingly.</P
-><P
->The device driver assumes a bulk packet size of 64 bytes, so this
-value should be used in the endpoint descriptors in the enumeration
-data provided by application code. There is experimental code
-for running with <A
-HREF="devs-usb-sa11x0.html#AEN18808"
->DMA disabled</A
->,
-in which case the packet size will be 16 bytes rather than 64.</P
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN18789"
-></A
-><H2
->Devtab Entries</H2
-><P
->In addition to the endpoint data structures the SA11X0 USB device
-driver can also provide devtab entries for each endpoint. This allows
-higher-level code to use traditional I/O operations such as
-<TT
-CLASS="FUNCTION"
->open</TT
->/<TT
-CLASS="FUNCTION"
->read</TT
->/<TT
-CLASS="FUNCTION"
->write</TT
->
-rather than the USB-specific non-blocking functions like
-<TT
-CLASS="FUNCTION"
->usbs_start_rx_buffer</TT
->. These devtab entries are
-optional since they are not always required. The relevant
-configuration options are
-<TT
-CLASS="LITERAL"
->CYGVAR_DEVS_USB_SA11X0_EP0_DEVTAB_ENTRY</TT
->,
-<TT
-CLASS="LITERAL"
->CYGVAR_DEVS_USB_SA11X0_EP1_DEVTAB_ENTRY</TT
-> and
-<TT
-CLASS="LITERAL"
->CYGVAR_DEVS_USB_SA11X0_EP2_DEVTAB_ENTRY</TT
->. By default
-these devtab entries are provided if the global preference
-<TT
-CLASS="LITERAL"
->CYGGLO_USB_SLAVE_PROVIDE_DEVTAB_ENTRIES</TT
-> is enabled,
-which is usually the case. Obviously a devtab entry for a given
-endpoint will only be provided if the underlying endpoint is enabled.
-For example, there will not be a devtab entry for endpoint 1 if
-<TT
-CLASS="LITERAL"
->CYGPKG_DEVS_USB_SA11X0_EP1</TT
-> is disabled.</P
-><P
->The names for the three devtab entries are determined by using a
-configurable base name and appending <TT
-CLASS="LITERAL"
->0c</TT
->,
-<TT
-CLASS="LITERAL"
->1r</TT
-> or <TT
-CLASS="LITERAL"
->2w</TT
->. The base name is
-determined by the configuration option
-<TT
-CLASS="LITERAL"
->CYGDAT_DEVS_USB_SA11X0_DEVTAB_BASENAME</TT
-> and has a
-default value of <TT
-CLASS="LITERAL"
->/dev/usbs</TT
->, so the devtab entry for
-endpoint 1 would default to <TT
-CLASS="LITERAL"
->/dev/usbs1r</TT
->. If the
-target hardware involves multiple USB devices then application
-developers may have to change the base name to prevent a name clash.</P
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN18808"
-></A
-><H2
->DMA Engines</H2
-><P
->The SA11X0 UDC provides only limited fifos for bulk transfers on
-endpoints 1 and 2; smaller than the normal 64-byte bulk packet size.
-Therefore a typical transfer requires the use of DMA engines. The
-SA11x0 provides six DMA engines that can be used for this, and the
-endpoints require one each (assuming both endpoints are enabled). At
-the time of writing there is no arbitration mechanism to control
-access to the DMA engines. By default the device driver will use
-DMA engine 4 for endpoint 1 and DMA engine 5 for endpoint 2, and it
-assumes that no other code uses these particular engines.</P
-><P
->The exact DMA engines that will be used are determined by the
-configuration options
-<TT
-CLASS="LITERAL"
->CYGNUM_DEVS_USB_SA11X0_EP1_DMA_CHANNEL</TT
-> and
-<TT
-CLASS="LITERAL"
->CYGNUM_DEVS_USB_SA11X0_EP2_DMA_CHANNEL</TT
->. These
-options have the booldata flavor, allowing the use of DMA to be
-disabled completely in addition to controlling which DMA engines are
-used. If DMA is disabled then the device driver will attempt to
-work purely using the fifos, and the packet size will be limited to
-only 16 bytes. This limit should be reflected in the appropriate
-endpoint descriptors in the enumeration data. The code for driving the
-endpoints without DMA should be considered experimental. At best it
-will be suitable only for applications where the amount of data
-transferred is relatively small, because four times as many interrupts
-will be raised and performance will suffer accordingly.</P
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