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<!-- Copyright (C) 2001 Red Hat, Inc. -->
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<!-- standard (paper) book form is prohibited unless prior -->
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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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>NEC uPD985xx USB Device Driver</TITLE
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><meta name="MSSmartTagsPreventParsing" content="TRUE">
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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"></HEAD
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VLINK="#840084"
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ALINK="#0000FF"
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><H1
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><A
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NAME="DEVS-USB-NEC-UPD985XX"
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>NEC uPD985xx USB Device Driver</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="AEN4"
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></A
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><H2
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>Name</H2
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>NEC uPD985xx USB Support -- Device driver for the on-chip NEC uPD985xx USB device</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN7"
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></A
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><H2
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>NEC uPD985xx USB Hardware</H2
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><P
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>The NEC uPD985xx family of processors is supplied with an on-chip USB
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slave device, the UDC (USB Device Controller). This supports seven
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endpoints. Endpoint 0 can only be used for control messages. Endpoints
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1 and 2 are for isochronous transmits and receives respectively.
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Endpoints 3 and 4 support bulk transmits and receives. Endpoints 5 and
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6 normally support interrupt transmits and receives,but endpoint 5 can
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also be configured to support bulk transmits. At this time only the
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control endpoint 0, the bulk endpoints 3 and 4, and the interrupt
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endpoint 5 are supported.</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="AEN10"
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></A
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><H2
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>Endpoint Data Structures</H2
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><P
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>The uPD985xx USB device driver can provide up to four data structures
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corresponding to the four supported endpoints: a
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<SPAN
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CLASS="STRUCTNAME"
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>usbs_control_endpoint</SPAN
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> structure
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<TT
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CLASS="VARNAME"
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>usbs_upd985xx_ep0</TT
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>;
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<SPAN
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CLASS="STRUCTNAME"
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>usbs_tx_endpoint</SPAN
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> structures
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<TT
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CLASS="VARNAME"
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>usbs_upd985xx_ep3</TT
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> and
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<TT
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CLASS="VARNAME"
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>usbs_upd985xx_ep5</TT
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>; and a
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<SPAN
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CLASS="STRUCTNAME"
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>usbs_rx_endpoint</SPAN
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>
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<TT
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CLASS="VARNAME"
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>usbs_upd985xx_ep4</TT
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>. The header file
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<TT
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CLASS="FILENAME"
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>cyg/io/usb/usbs_nec_upd985xx.h</TT
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>
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provides declarations for these.</P
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><P
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>Not all applications will require support for all the endpoints. For
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example, if the intended use of the UDC only involves peripheral to
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host transfers then <TT
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CLASS="LITERAL"
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>usbs_upd985xx_ep4</TT
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> is redundant.
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The device driver provides configuration options to control the
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presence of each endpoint:</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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>Endpoint 0 is controlled by
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<TT
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CLASS="LITERAL"
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>CYGFUN_DEVS_USB_UPD985XX_EP0</TT
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>. This defaults to
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enabled if there are any higher-level packages that require USB
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hardware or if the global preference
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<TT
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CLASS="LITERAL"
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>CYGGLO_IO_USB_SLAVE_APPLICATION</TT
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> is enabled,
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otherwise it is disabled. Usually this has the desired effect. It may
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be necessary to override this in special circumstances, for example if
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the target board uses an external USB chip in preference to the UDC
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and it is that external chip's device driver that should be used
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rather than the on-chip UDC. It is not possible to disable endpoint 0
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and at the same time enable one or both of the other endpoints, since
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a USB device is only usable if it can process the standard control
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messages.</P
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></LI
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><LI
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><P
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>Endpoint 3 is controlled by
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<TT
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CLASS="LITERAL"
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>CYGPKG_DEVS_USB_UPD985XX_EP3</TT
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>. By default this
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endpoint is disabled: according to NEC erratum U3 there may be
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problems when attempting bulk transfers of 192 bytes or greater. As an
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alternative the device driver provides endpoint 5 configured to
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support bulk transfers. Endpoint 3 can be enabled if the application
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only requires bulk transfers of less than 192 bytes, or if this
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erratum is not applicable to the system being developed for other
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reasons.</P
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></LI
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><LI
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><P
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>Similarly endpoint 4 is controlled by
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<TT
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CLASS="LITERAL"
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>CYGPKG_DEVS_USB_UPD985XX_EP4</TT
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>. This is enabled by
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default whenever endpoint 0 is enabled, but it can be disabled
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manually.</P
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></LI
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><LI
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><P
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>Endpoint 5 is controlled by
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<TT
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CLASS="LITERAL"
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>CYGPKG_DEVS_USB_UPD985XX_EP5</TT
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>. This is enabled by
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default whenever endpoint 0 is enabled, but it can be disabled
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manually. There is also a configuration option
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<TT
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CLASS="LITERAL"
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>CYGIMP_DEVS_USB_UPD985XX_EP5_BULK</TT
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>, enabled by
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default. This option allows the endpoint to be used for bulk
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transfers rather than interrupt transfers.</P
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></LI
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></OL
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><P
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>The uPD985xx USB device driver implements the interface specified by the
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common eCos USB Slave Support package. The documentation for that
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package should be consulted for further details. </P
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><P
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>The device driver assumes a bulk packet size of 64 bytes, so this
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value should be used in the endpoint descriptors in the enumeration
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data provided by application code. The device driver also assumes
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a control packet size of eight bytes, and again this should be
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reflected in the enumeration data. If endpoint 5 is configured for
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interrupt rather than bulk transfers then the maximum packet size is
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limited to 64 bytes by the USB standard.</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="AEN40"
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></A
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><H2
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>Devtab Entries</H2
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><P
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>In addition to the endpoint data structures the uPD985xx USB device
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driver can also provide devtab entries for each endpoint. This allows
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higher-level code to use traditional I/O operations such as
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<TT
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CLASS="FUNCTION"
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>open</TT
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>/<TT
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CLASS="FUNCTION"
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>read</TT
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>/<TT
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CLASS="FUNCTION"
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>write</TT
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>
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rather than the USB-specific non-blocking functions like
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<TT
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CLASS="FUNCTION"
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>usbs_start_rx_buffer</TT
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>. These devtab entries are
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optional since they are not always required. The relevant
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configuration options are
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<TT
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CLASS="LITERAL"
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>CYGVAR_DEVS_USB_UPD985XX_EP0_DEVTAB_ENTRY</TT
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>,
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<TT
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CLASS="LITERAL"
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>CYGVAR_DEVS_USB_UPD985XX_EP3_DEVTAB_ENTRY</TT
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>,
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<TT
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CLASS="LITERAL"
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>CYGVAR_DEVS_USB_UPD985XX_EP4_DEVTAB_ENTRY</TT
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>, and
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<TT
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CLASS="LITERAL"
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>CYGVAR_DEVS_USB_UPD985XX_EP5_DEVTAB_ENTRY</TT
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>. By
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default these devtab entries are provided if the global preference
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<TT
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CLASS="LITERAL"
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>CYGGLO_USB_SLAVE_PROVIDE_DEVTAB_ENTRIES</TT
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> is enabled,
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which is usually the case. Obviously a devtab entry for a given
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endpoint will only be provided if the underlying endpoint is enabled.
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For example, there will not be a devtab entry for endpoint 4 if
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<TT
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| 245 |
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CLASS="LITERAL"
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>CYGPKG_DEVS_USB_UPD985XX_EP4</TT
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> is disabled.</P
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><P
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>The names for the devtab entries are determined by using a
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configurable base name and appending <TT
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CLASS="LITERAL"
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>0c</TT
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>,
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<TT
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CLASS="LITERAL"
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>3w</TT
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>, <TT
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CLASS="LITERAL"
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>4r</TT
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> or <TT
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CLASS="LITERAL"
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>5w</TT
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>.
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The base name is determined by the configuration option
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<TT
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CLASS="LITERAL"
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>CYGDAT_DEVS_USB_UPD985XX_DEVTAB_BASENAME</TT
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> and has a
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default value of <TT
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CLASS="LITERAL"
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>/dev/usbs</TT
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>, so the devtab entry for
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endpoint 4 would default to <TT
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CLASS="LITERAL"
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>/dev/usbs4r</TT
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>. If the
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target hardware involves multiple USB devices then application
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| 278 |
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developers may have to change the base name to prevent a name clash
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with other USB device drivers.</P
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| 280 |
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></DIV
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| 281 |
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><DIV
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| 282 |
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CLASS="REFSECT1"
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><A
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| 284 |
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NAME="AEN61"
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| 285 |
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></A
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| 286 |
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><H2
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>Restrictions</H2
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| 288 |
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><P
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| 289 |
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>The current device driver imposes a restriction on certain bulk
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receives on endpoint 4. If the protocol being used involves
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variable-length transfers, in other words if the host is allowed to
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| 292 |
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send less data than a maximum-sized transfer, then the buffer passed
|
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to the device driver for receives must be aligned to a 16-byte
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| 294 |
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cacheline boundary and it must be a multiple of this 16-byte cacheline
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size. This restriction does not apply if the protocol only involves
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| 296 |
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fixed-size transfers.</P
|
| 297 |
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|
></DIV
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| 298 |
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><DIV
|
| 299 |
|
|
CLASS="REFSECT1"
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| 300 |
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><A
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| 301 |
|
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NAME="AEN64"
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></A
|
| 303 |
|
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><H2
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| 304 |
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>Optional Hardware Workarounds</H2
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| 305 |
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><P
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| 306 |
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>The NEC errata list a number of other problems that affect the
|
| 307 |
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USB device driver. The device driver contains workarounds for these,
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| 308 |
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which are enabled by default but can be disabled if the application
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| 309 |
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developer knows that the relevant errata are not relevant to the
|
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system being developed.</P
|
| 311 |
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><P
|
| 312 |
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>Erratum S1 lists a possible problem if the device driver attempts
|
| 313 |
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multiple writes to the USB hardware. This is circumvented by a
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| 314 |
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dummy read operation after every write. If this workaround is not
|
| 315 |
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required then the configuration option
|
| 316 |
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<TT
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| 317 |
|
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CLASS="LITERAL"
|
| 318 |
|
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>CYGIMP_DEVS_USB_UPD985XX_IBUS_WRITE_LIMIT</TT
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| 319 |
|
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> can be disabled.</P
|
| 320 |
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><P
|
| 321 |
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|
>Errata U3 and U4 describe various problems related to concurrent
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| 322 |
|
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transmissions on different endpoints. By default the device driver
|
| 323 |
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works around this by serializing all transmit operations. For example
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| 324 |
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if the device driver needs to send a response to a control message on
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| 325 |
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endpoint 0 while there is an ongoing bulk transfer on endpoint 5, the
|
| 326 |
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response is delayed until the bulk transfer has completed. Under
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| 327 |
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typical operating conditions this does not cause any problems:
|
| 328 |
|
|
endpoint 0 traffic usually happens only during initialization, when
|
| 329 |
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|
the target is connected to the host, while endpoint 5 traffic only
|
| 330 |
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|
happens after initialization. However if transmit serialization is
|
| 331 |
|
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inappropriate for the system being developed then it can be disabled
|
| 332 |
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|
using the configuration option
|
| 333 |
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|
<TT
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| 334 |
|
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CLASS="LITERAL"
|
| 335 |
|
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>CYGIMP_DEVS_USB_UPD985XX_SERIALIZE_TRANSMITS</TT
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| 336 |
|
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>. </P
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| 337 |
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></DIV
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| 338 |
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><DIV
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| 339 |
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CLASS="REFSECT1"
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><A
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| 341 |
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NAME="AEN71"
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| 342 |
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></A
|
| 343 |
|
|
><H2
|
| 344 |
|
|
>Platform Dependencies</H2
|
| 345 |
|
|
><P
|
| 346 |
|
|
>On some platforms it is necessary for the low-level USB device driver
|
| 347 |
|
|
to perform some additional operations during start-up. For example it
|
| 348 |
|
|
may be necessary to manipulate one of the processor's GPIO lines
|
| 349 |
|
|
before the host can detect a new USB peripheral and attempt to
|
| 350 |
|
|
communicate with it. This avoids problems if the target involves a
|
| 351 |
|
|
significant amount of work prior to device driver initialization, for
|
| 352 |
|
|
example a power-on self-test sequence. If the USB host attempted to
|
| 353 |
|
|
contact the target before the USB device driver had been initialized,
|
| 354 |
|
|
it would fail to get the expected responses and conclude that the
|
| 355 |
|
|
target was not a functional USB peripheral.</P
|
| 356 |
|
|
><P
|
| 357 |
|
|
>Platform-specific initialization code can be provided via a macro
|
| 358 |
|
|
<TT
|
| 359 |
|
|
CLASS="FUNCTION"
|
| 360 |
|
|
>UPD985XX_USB_PLATFORM_INIT</TT
|
| 361 |
|
|
>. Typically this macro
|
| 362 |
|
|
would be defined in the platform HAL's header file
|
| 363 |
|
|
<TT
|
| 364 |
|
|
CLASS="FILENAME"
|
| 365 |
|
|
>cyg/hal/plf_io.h</TT
|
| 366 |
|
|
>. If the
|
| 367 |
|
|
current platform defines such a macro, the USB device driver will
|
| 368 |
|
|
invoke it during the endpoint 0 start-up operation.</P
|
| 369 |
|
|
></DIV
|
| 370 |
|
|
></BODY
|
| 371 |
|
|
></HTML
|
| 372 |
|
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>
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