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<HTML
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><HEAD
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><TITLE
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>Writing a USB Device Driver</TITLE
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REL="HOME"
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HREF="ecos-ref.html"><LINK
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REL="UP"
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TITLE="eCos USB Slave Support"
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HREF="io-usb-slave.html"><LINK
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="USBS-WRITING">Writing a USB Device Driver</H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN16705"
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></A
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><H2
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>Name</H2
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>Writing a USB Device Driver -- USB Device Driver Porting Guide</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN16708"
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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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>Often the best way to write a USB device driver will be to start with
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an existing one and modify it as necessary. The information given here
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is intended primarily as an outline rather than as a complete guide.</P
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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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><B
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>Note: </B
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>At the time of writing only one USB device driver has been
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implemented. Hence it is possible, perhaps probable, that some
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portability issues have not yet been addressed. One issue
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involves the different types of transfer, for example the initial
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target hardware had no support for isochronous or interrupt transfers,
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so additional functionality may be needed to switch between transfer
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types. Another issue would be hardware where a given endpoint number,
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say endpoint 1, could be used for either receiving or transmitting
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data, but not both because a single fifo is used. Issues like these
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will have to be resolved as and when additional USB device drivers are
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written.</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="AEN16713"
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></A
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><H2
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>The Control Endpoint</H2
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><P
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>A USB device driver should provide a single <A
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HREF="usbs-control.html"
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><SPAN
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CLASS="STRUCTNAME"
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>usbs_control_endpoint</SPAN
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></A
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>
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data structure for every USB device. Typical peripherals will have
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only one USB port so there will be just one such data structure in the
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entire system, but theoretically it is possible to have multiple USB
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devices. These may all involve the same chip, in which case a single
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device driver should support multiple device instances, or they may
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involve different chips. The name or names of these data structures
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are determined by the device driver, but appropriate care should be
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taken to avoid name clashes. </P
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><P
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>A USB device cannot be used unless the control endpoint data structure
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exists. However, the presence of USB hardware in the target processor
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or board does not guarantee that the application will necessarily want
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to use that hardware. To avoid unwanted code or data overheads, the
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device driver can provide a configuration option to determine whether
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or not the endpoint 0 data structure is actually provided. A default
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value of <TT
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CLASS="LITERAL"
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>CYGINT_IO_USB_SLAVE_CLIENTS</TT
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> ensures that
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the USB driver will be enabled automatically if higher-level code does
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require USB support, while leaving ultimate control to the user.</P
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><P
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>The USB device driver is responsible for filling in the
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<TT
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CLASS="STRUCTFIELD"
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><I
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>start_fn</I
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></TT
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>,
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<TT
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CLASS="STRUCTFIELD"
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><I
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>poll_fn</I
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></TT
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> and
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<TT
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CLASS="STRUCTFIELD"
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><I
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>interrupt_vector</I
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></TT
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> fields. Usually this can
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be achieved by static initialization. The driver is also largely
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responsible for maintaining the <TT
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CLASS="STRUCTFIELD"
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><I
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>state</I
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></TT
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>
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field. The <TT
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CLASS="STRUCTFIELD"
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><I
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>control_buffer</I
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></TT
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> array should be
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used to hold the first packet of a control message. The
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<TT
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CLASS="STRUCTFIELD"
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><I
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>buffer</I
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></TT
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> and other fields related to data
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transfers will be managed <A
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HREF="usbs-control.html#AEN16615"
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>jointly</A
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> by higher-level code and
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the device driver. The remaining fields are generally filled in by
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higher-level code, although the driver should initialize them to NULL
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values.</P
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><P
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>Hardware permitting, the USB device should be inactive until the
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<TT
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CLASS="STRUCTFIELD"
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><I
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>start_fn</I
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></TT
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> is invoked, for example by
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tristating the appropriate pins. This prevents the host from
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interacting with the peripheral before all other parts of the system
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have initialized. It is expected that the
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<TT
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CLASS="STRUCTFIELD"
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><I
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>start_fn</I
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></TT
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> will only be invoked once, shortly
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after power-up.</P
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><P
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>Where possible the device driver should detect state changes, such as
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when the connection between host and peripheral is established, and
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<A
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HREF="usbs-control.html#AEN16552"
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>report</A
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|
> these to higher-level
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code via the <TT
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CLASS="STRUCTFIELD"
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><I
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>state_change_fn</I
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></TT
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> callback, if
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any. The state change to and from configured state cannot easily be
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handled by the device driver itself, instead higher-level code such as
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the common USB slave package will take care of this.</P
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><P
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>Once the connection between host and peripheral has been established,
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the peripheral must be ready to accept control messages at all times,
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and must respond to these within certain time constraints. For
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example, the standard set-address control message must be handled
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within 50ms. The USB specification provides more information on these
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constraints. The device driver is responsible for receiving the
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| 247 |
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initial packet of a control message. This packet will always be eight
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| 248 |
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bytes and should be stored in the
|
| 249 |
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<TT
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| 250 |
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CLASS="STRUCTFIELD"
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| 251 |
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><I
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| 252 |
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>control_buffer</I
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></TT
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| 254 |
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> field. Certain standard
|
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control messages should be detected and handled by the device driver
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| 256 |
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itself. The most important is set-address, but usually the get-status,
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set-feature and clear-feature requests when applied to halted
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| 258 |
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endpoints should also be handled by the driver. Other standard control
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| 259 |
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messages should first be passed on to the
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| 260 |
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<TT
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| 261 |
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|
CLASS="STRUCTFIELD"
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| 262 |
|
|
><I
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| 263 |
|
|
>standard_control_fn</I
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| 264 |
|
|
></TT
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| 265 |
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> callback (if any), and
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finally to the default handler
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<TT
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| 268 |
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CLASS="FUNCTION"
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>usbs_handle_standard_control</TT
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| 270 |
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> provided by the
|
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common USB slave package. Class, vendor and reserved control messages
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| 272 |
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should always be dispatched to the appropriate callback and there is
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no default handler for these.</P
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| 274 |
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><P
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| 275 |
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>Some control messages will involve further data transfer, not just the
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| 276 |
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initial packet. The device driver must handle this in accordance with
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| 277 |
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the USB specification and the <A
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| 278 |
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HREF="usbs-control.html#AEN16615"
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| 279 |
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>buffer management strategy</A
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| 280 |
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>. The
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| 281 |
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driver is also responsible for keeping track of whether or not the
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| 282 |
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control operation has succeeded and generating an ACK or STALL
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| 283 |
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handshake. </P
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| 284 |
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|
><P
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| 285 |
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>The polling support is optional and may not be feasible on all
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| 286 |
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hardware. It is only used in certain specialised environments such as
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| 287 |
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RedBoot. A typical implementation of the polling function would just
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check whether or not an interrupt would have occurred and, if so, call
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| 289 |
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the same code that the interrupt handler would.</P
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| 290 |
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></DIV
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| 291 |
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><DIV
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| 292 |
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CLASS="REFSECT1"
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><A
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NAME="AEN16741"
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| 295 |
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></A
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| 296 |
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><H2
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| 297 |
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>Data Endpoints</H2
|
| 298 |
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><P
|
| 299 |
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>In addition to the control endpoint data structure, a USB device
|
| 300 |
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driver should also provide appropriate <A
|
| 301 |
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HREF="usbs-data.html"
|
| 302 |
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|
>data
|
| 303 |
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endpoint</A
|
| 304 |
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|
> data structures. Obviously this is only relevant if
|
| 305 |
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the USB support generally is desired, that is if the control endpoint is
|
| 306 |
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provided. In addition, higher-level code may not require all the
|
| 307 |
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|
endpoints, so it may be useful to provide configuration options that
|
| 308 |
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control the presence of each endpoint. For example, the intended
|
| 309 |
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application might only involve a single transmit endpoint and of
|
| 310 |
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course control messages, so supporting receive endpoints might waste
|
| 311 |
|
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memory.</P
|
| 312 |
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><P
|
| 313 |
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>Conceptually, data endpoints are much simpler than the control
|
| 314 |
|
|
endpoint. The device driver has to supply two functions, one for
|
| 315 |
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data transfers and another to control the halted condition. These
|
| 316 |
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|
implement the functionality for
|
| 317 |
|
|
<A
|
| 318 |
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HREF="usbs-start-rx.html"
|
| 319 |
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><TT
|
| 320 |
|
|
CLASS="FUNCTION"
|
| 321 |
|
|
>usbs_start_rx_buffer</TT
|
| 322 |
|
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></A
|
| 323 |
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>,
|
| 324 |
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<A
|
| 325 |
|
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HREF="usbs-start-tx.html"
|
| 326 |
|
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><TT
|
| 327 |
|
|
CLASS="FUNCTION"
|
| 328 |
|
|
>usbs_start_tx_buffer</TT
|
| 329 |
|
|
></A
|
| 330 |
|
|
>,
|
| 331 |
|
|
<A
|
| 332 |
|
|
HREF="usbs-halt.html"
|
| 333 |
|
|
><TT
|
| 334 |
|
|
CLASS="FUNCTION"
|
| 335 |
|
|
>usbs_set_rx_endpoint_halted</TT
|
| 336 |
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></A
|
| 337 |
|
|
> and
|
| 338 |
|
|
<A
|
| 339 |
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HREF="usbs-halt.html"
|
| 340 |
|
|
><TT
|
| 341 |
|
|
CLASS="FUNCTION"
|
| 342 |
|
|
>usbs_set_tx_endpoint_halted</TT
|
| 343 |
|
|
></A
|
| 344 |
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|
>.
|
| 345 |
|
|
The device driver is also responsible for maintaining the
|
| 346 |
|
|
<TT
|
| 347 |
|
|
CLASS="STRUCTFIELD"
|
| 348 |
|
|
><I
|
| 349 |
|
|
>halted</I
|
| 350 |
|
|
></TT
|
| 351 |
|
|
> status.</P
|
| 352 |
|
|
><P
|
| 353 |
|
|
>For data transfers, higher-level code will have filled in the
|
| 354 |
|
|
<TT
|
| 355 |
|
|
CLASS="STRUCTFIELD"
|
| 356 |
|
|
><I
|
| 357 |
|
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>buffer</I
|
| 358 |
|
|
></TT
|
| 359 |
|
|
>,
|
| 360 |
|
|
<TT
|
| 361 |
|
|
CLASS="STRUCTFIELD"
|
| 362 |
|
|
><I
|
| 363 |
|
|
>buffer_size</I
|
| 364 |
|
|
></TT
|
| 365 |
|
|
>,
|
| 366 |
|
|
<TT
|
| 367 |
|
|
CLASS="STRUCTFIELD"
|
| 368 |
|
|
><I
|
| 369 |
|
|
>complete_fn</I
|
| 370 |
|
|
></TT
|
| 371 |
|
|
> and
|
| 372 |
|
|
<TT
|
| 373 |
|
|
CLASS="STRUCTFIELD"
|
| 374 |
|
|
><I
|
| 375 |
|
|
>complete_data</I
|
| 376 |
|
|
></TT
|
| 377 |
|
|
> fields. The transfer function
|
| 378 |
|
|
should arrange for the transfer to start, allowing the host to send or
|
| 379 |
|
|
receive packets. Typically this will result in an interrupt at the end
|
| 380 |
|
|
of the transfer or after each packet. Once the entire transfer has
|
| 381 |
|
|
been completed, the driver's interrupt handling code should invoke the
|
| 382 |
|
|
completion function. This can happen either in DSR context or thread
|
| 383 |
|
|
context, depending on the driver's implementation. There are a number
|
| 384 |
|
|
of special cases to consider. If the endpoint is halted when the
|
| 385 |
|
|
transfer is started then the completion function can be invoked
|
| 386 |
|
|
immediately with <TT
|
| 387 |
|
|
CLASS="LITERAL"
|
| 388 |
|
|
>-EAGAIN</TT
|
| 389 |
|
|
>. If the transfer cannot be
|
| 390 |
|
|
completed because the connection is broken then the completion
|
| 391 |
|
|
function should be invoked with <TT
|
| 392 |
|
|
CLASS="LITERAL"
|
| 393 |
|
|
>-EPIPE</TT
|
| 394 |
|
|
>. If the
|
| 395 |
|
|
endpoint is stalled during the transfer, either because of a standard
|
| 396 |
|
|
control message or because higher-level code calls the appropriate
|
| 397 |
|
|
<TT
|
| 398 |
|
|
CLASS="STRUCTFIELD"
|
| 399 |
|
|
><I
|
| 400 |
|
|
>set_halted_fn</I
|
| 401 |
|
|
></TT
|
| 402 |
|
|
>, then again the completion
|
| 403 |
|
|
function should be invoked with <TT
|
| 404 |
|
|
CLASS="LITERAL"
|
| 405 |
|
|
>-EAGAIN</TT
|
| 406 |
|
|
>. Finally,
|
| 407 |
|
|
the <<TT
|
| 408 |
|
|
CLASS="FUNCTION"
|
| 409 |
|
|
>usbs_start_rx_endpoint_wait</TT
|
| 410 |
|
|
> and
|
| 411 |
|
|
<TT
|
| 412 |
|
|
CLASS="FUNCTION"
|
| 413 |
|
|
>usbs_start_tx_endpoint_wait</TT
|
| 414 |
|
|
> functions involve
|
| 415 |
|
|
calling the device driver's data transfer function with a buffer size
|
| 416 |
|
|
of 0 bytes.</P
|
| 417 |
|
|
><DIV
|
| 418 |
|
|
CLASS="NOTE"
|
| 419 |
|
|
><BLOCKQUOTE
|
| 420 |
|
|
CLASS="NOTE"
|
| 421 |
|
|
><P
|
| 422 |
|
|
><B
|
| 423 |
|
|
>Note: </B
|
| 424 |
|
|
>Giving a buffer size of 0 bytes a special meaning is problematical
|
| 425 |
|
|
because it prevents transfers of that size. Such transfers are allowed
|
| 426 |
|
|
by the USB protocol, consisting of just headers and acknowledgements
|
| 427 |
|
|
and an empty data phase, although rarely useful. A future modification
|
| 428 |
|
|
of the device driver specification will address this issue, although
|
| 429 |
|
|
care has to be taken that the functionality remains accessible through
|
| 430 |
|
|
devtab entries as well as via low-level accesses.</P
|
| 431 |
|
|
></BLOCKQUOTE
|
| 432 |
|
|
></DIV
|
| 433 |
|
|
></DIV
|
| 434 |
|
|
><DIV
|
| 435 |
|
|
CLASS="REFSECT1"
|
| 436 |
|
|
><A
|
| 437 |
|
|
NAME="AEN16768"
|
| 438 |
|
|
></A
|
| 439 |
|
|
><H2
|
| 440 |
|
|
>Devtab Entries</H2
|
| 441 |
|
|
><P
|
| 442 |
|
|
>For some applications or higher-level packages it may be more
|
| 443 |
|
|
convenient to use traditional open/read/write I/O calls rather than
|
| 444 |
|
|
the non-blocking USB I/O calls. To support this the device driver can
|
| 445 |
|
|
provide a devtab entry for each endpoint, for example:</P
|
| 446 |
|
|
><TABLE
|
| 447 |
|
|
BORDER="5"
|
| 448 |
|
|
BGCOLOR="#E0E0F0"
|
| 449 |
|
|
WIDTH="70%"
|
| 450 |
|
|
><TR
|
| 451 |
|
|
><TD
|
| 452 |
|
|
><PRE
|
| 453 |
|
|
CLASS="PROGRAMLISTING"
|
| 454 |
|
|
>#ifdef CYGVAR_DEVS_USB_SA11X0_EP1_DEVTAB_ENTRY
|
| 455 |
|
|
|
| 456 |
|
|
static CHAR_DEVIO_TABLE(usbs_sa11x0_ep1_devtab_functions,
|
| 457 |
|
|
&cyg_devio_cwrite,
|
| 458 |
|
|
&usbs_devtab_cread,
|
| 459 |
|
|
&cyg_devio_bwrite,
|
| 460 |
|
|
&cyg_devio_bread,
|
| 461 |
|
|
&cyg_devio_select,
|
| 462 |
|
|
&cyg_devio_get_config,
|
| 463 |
|
|
&cyg_devio_set_config);
|
| 464 |
|
|
|
| 465 |
|
|
static CHAR_DEVTAB_ENTRY(usbs_sa11x0_ep1_devtab_entry,
|
| 466 |
|
|
CYGDAT_DEVS_USB_SA11X0_DEVTAB_BASENAME "1r",
|
| 467 |
|
|
0,
|
| 468 |
|
|
&usbs_sa11x0_ep1_devtab_functions,
|
| 469 |
|
|
&usbs_sa11x0_devtab_dummy_init,
|
| 470 |
|
|
0,
|
| 471 |
|
|
(void*) &usbs_sa11x0_ep1);
|
| 472 |
|
|
#endif</PRE
|
| 473 |
|
|
></TD
|
| 474 |
|
|
></TR
|
| 475 |
|
|
></TABLE
|
| 476 |
|
|
><P
|
| 477 |
|
|
>Again care must be taken to avoid name clashes. This can be achieved
|
| 478 |
|
|
by having a configuration option to control the base name, with a
|
| 479 |
|
|
default value of e.g. <TT
|
| 480 |
|
|
CLASS="LITERAL"
|
| 481 |
|
|
>/dev/usbs</TT
|
| 482 |
|
|
>, and appending an
|
| 483 |
|
|
endpoint-specific string. This gives the application developer
|
| 484 |
|
|
sufficient control to eliminate any name clashes. The common USB slave
|
| 485 |
|
|
package provides functions <TT
|
| 486 |
|
|
CLASS="FUNCTION"
|
| 487 |
|
|
>usbs_devtab_cwrite</TT
|
| 488 |
|
|
> and
|
| 489 |
|
|
<TT
|
| 490 |
|
|
CLASS="FUNCTION"
|
| 491 |
|
|
>usbs_devtab_cread</TT
|
| 492 |
|
|
>, which can be used in the
|
| 493 |
|
|
function tables for transmit and receive endpoints respectively. The
|
| 494 |
|
|
private field <TT
|
| 495 |
|
|
CLASS="STRUCTFIELD"
|
| 496 |
|
|
><I
|
| 497 |
|
|
>priv</I
|
| 498 |
|
|
></TT
|
| 499 |
|
|
> of the devtab entry
|
| 500 |
|
|
should be a pointer to the underlying endpoint data structure.</P
|
| 501 |
|
|
><P
|
| 502 |
|
|
>Because devtab entries are never accessed directly, only indirectly,
|
| 503 |
|
|
they would usually be eliminated by the linker. To avoid this the
|
| 504 |
|
|
devtab entries should normally be defined in a separate source file
|
| 505 |
|
|
which ends up the special library <TT
|
| 506 |
|
|
CLASS="FILENAME"
|
| 507 |
|
|
>libextras.a</TT
|
| 508 |
|
|
>
|
| 509 |
|
|
rather than in the default library <TT
|
| 510 |
|
|
CLASS="FILENAME"
|
| 511 |
|
|
>libtarget.a</TT
|
| 512 |
|
|
>.</P
|
| 513 |
|
|
><P
|
| 514 |
|
|
>Not all applications or higher-level packages will want to use the
|
| 515 |
|
|
devtab entries and the blocking I/O facilities. It may be appropriate
|
| 516 |
|
|
for the device driver to provide additional configuration options that
|
| 517 |
|
|
control whether or not any or all of the devtab entries should be
|
| 518 |
|
|
provided, to avoid unnecessary memory overheads.</P
|
| 519 |
|
|
></DIV
|
| 520 |
|
|
><DIV
|
| 521 |
|
|
CLASS="REFSECT1"
|
| 522 |
|
|
><A
|
| 523 |
|
|
NAME="AEN16781"
|
| 524 |
|
|
></A
|
| 525 |
|
|
><H2
|
| 526 |
|
|
>Interrupt Handling</H2
|
| 527 |
|
|
><P
|
| 528 |
|
|
>A typical USB device driver will need to service interrupts for all of
|
| 529 |
|
|
the endpoints and possibly for additional USB events such as entering
|
| 530 |
|
|
or leaving suspended mode. Usually these interrupts need not be
|
| 531 |
|
|
serviced directly by the ISR. Instead, they can be left to a DSR. If
|
| 532 |
|
|
the peripheral is not able to accept or send another packet just yet,
|
| 533 |
|
|
the hardware will generate a NAK and the host will just retry a little
|
| 534 |
|
|
bit later. If high throughput is required then it may be desirable to
|
| 535 |
|
|
handle the bulk transfer protocol largely at ISR level, that is take
|
| 536 |
|
|
care of each packet in the ISR and only activate the DSR once the
|
| 537 |
|
|
whole transfer has completed.</P
|
| 538 |
|
|
><P
|
| 539 |
|
|
>Control messages may involve invoking arbitrary callback functions in
|
| 540 |
|
|
higher-level code. This should normally happen at DSR level. Doing it
|
| 541 |
|
|
at ISR level could seriously affect the system's interrupt latency and
|
| 542 |
|
|
impose unacceptable constraints on what operations can be performed by
|
| 543 |
|
|
those callbacks. If the device driver requires a thread anyway then it
|
| 544 |
|
|
may be appropriate to use this thread for invoking the callbacks, but
|
| 545 |
|
|
usually it is not worthwhile to add a new thread to the system just
|
| 546 |
|
|
for this; higher-level code is expected to write callbacks that
|
| 547 |
|
|
function sensibly at DSR level. Much the same applies to the
|
| 548 |
|
|
completion functions associated with data transfers. These should also
|
| 549 |
|
|
be invoked at DSR or thread level.</P
|
| 550 |
|
|
></DIV
|
| 551 |
|
|
><DIV
|
| 552 |
|
|
CLASS="REFSECT1"
|
| 553 |
|
|
><A
|
| 554 |
|
|
NAME="AEN16785"
|
| 555 |
|
|
></A
|
| 556 |
|
|
><H2
|
| 557 |
|
|
>Support for USB Testing</H2
|
| 558 |
|
|
><P
|
| 559 |
|
|
>Optionally a USB device driver can provide support for the
|
| 560 |
|
|
<A
|
| 561 |
|
|
HREF="usbs-testing.html"
|
| 562 |
|
|
>USB test software</A
|
| 563 |
|
|
>. This requires
|
| 564 |
|
|
defining a number of additional data structures, allowing the
|
| 565 |
|
|
generic test code to work out just what the hardware is capable of and
|
| 566 |
|
|
hence what testing can be performed.</P
|
| 567 |
|
|
><P
|
| 568 |
|
|
>The key data structure is
|
| 569 |
|
|
<SPAN
|
| 570 |
|
|
CLASS="STRUCTNAME"
|
| 571 |
|
|
>usbs_testing_endpoint</SPAN
|
| 572 |
|
|
>, defined in <TT
|
| 573 |
|
|
CLASS="FILENAME"
|
| 574 |
|
|
>cyg/io/usb/usbs.h</TT
|
| 575 |
|
|
>. In addition some
|
| 576 |
|
|
commonly required constants are provided by the common USB package in
|
| 577 |
|
|
<TT
|
| 578 |
|
|
CLASS="FILENAME"
|
| 579 |
|
|
>cyg/io/usb/usb.h</TT
|
| 580 |
|
|
>. One
|
| 581 |
|
|
<SPAN
|
| 582 |
|
|
CLASS="STRUCTNAME"
|
| 583 |
|
|
>usbs_testing_endpoint</SPAN
|
| 584 |
|
|
> structure should be
|
| 585 |
|
|
defined for each supported endpoint. The following fields need to be
|
| 586 |
|
|
filled in:</P
|
| 587 |
|
|
><P
|
| 588 |
|
|
></P
|
| 589 |
|
|
><DIV
|
| 590 |
|
|
CLASS="VARIABLELIST"
|
| 591 |
|
|
><DL
|
| 592 |
|
|
><DT
|
| 593 |
|
|
><TT
|
| 594 |
|
|
CLASS="STRUCTFIELD"
|
| 595 |
|
|
><I
|
| 596 |
|
|
>endpoint_type</I
|
| 597 |
|
|
></TT
|
| 598 |
|
|
></DT
|
| 599 |
|
|
><DD
|
| 600 |
|
|
><P
|
| 601 |
|
|
> This specifies the type of endpoint and should be one of
|
| 602 |
|
|
<TT
|
| 603 |
|
|
CLASS="LITERAL"
|
| 604 |
|
|
>USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL</TT
|
| 605 |
|
|
>,
|
| 606 |
|
|
<TT
|
| 607 |
|
|
CLASS="LITERAL"
|
| 608 |
|
|
>BULK</TT
|
| 609 |
|
|
>, <TT
|
| 610 |
|
|
CLASS="LITERAL"
|
| 611 |
|
|
>ISOCHRONOUS</TT
|
| 612 |
|
|
> or
|
| 613 |
|
|
<TT
|
| 614 |
|
|
CLASS="LITERAL"
|
| 615 |
|
|
>INTERRUPT</TT
|
| 616 |
|
|
>.
|
| 617 |
|
|
</P
|
| 618 |
|
|
></DD
|
| 619 |
|
|
><DT
|
| 620 |
|
|
><TT
|
| 621 |
|
|
CLASS="STRUCTFIELD"
|
| 622 |
|
|
><I
|
| 623 |
|
|
>endpoint_number</I
|
| 624 |
|
|
></TT
|
| 625 |
|
|
></DT
|
| 626 |
|
|
><DD
|
| 627 |
|
|
><P
|
| 628 |
|
|
> This identifies the number that should be used by the host
|
| 629 |
|
|
to address this endpoint. For a control endpoint it should
|
| 630 |
|
|
be 0. For other types of endpoints it should be between
|
| 631 |
|
|
1 and 15.
|
| 632 |
|
|
</P
|
| 633 |
|
|
></DD
|
| 634 |
|
|
><DT
|
| 635 |
|
|
><TT
|
| 636 |
|
|
CLASS="STRUCTFIELD"
|
| 637 |
|
|
><I
|
| 638 |
|
|
>endpoint_direction</I
|
| 639 |
|
|
></TT
|
| 640 |
|
|
></DT
|
| 641 |
|
|
><DD
|
| 642 |
|
|
><P
|
| 643 |
|
|
> For control endpoints this field is irrelevant. For other
|
| 644 |
|
|
types of endpoint it should be either
|
| 645 |
|
|
<TT
|
| 646 |
|
|
CLASS="LITERAL"
|
| 647 |
|
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN</TT
|
| 648 |
|
|
> or
|
| 649 |
|
|
<TT
|
| 650 |
|
|
CLASS="LITERAL"
|
| 651 |
|
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_OUT</TT
|
| 652 |
|
|
>. If a given
|
| 653 |
|
|
endpoint number can be used for traffic in both directions then
|
| 654 |
|
|
there should be two entries in the array, one for each direction.
|
| 655 |
|
|
</P
|
| 656 |
|
|
></DD
|
| 657 |
|
|
><DT
|
| 658 |
|
|
><TT
|
| 659 |
|
|
CLASS="STRUCTFIELD"
|
| 660 |
|
|
><I
|
| 661 |
|
|
>endpoint</I
|
| 662 |
|
|
></TT
|
| 663 |
|
|
></DT
|
| 664 |
|
|
><DD
|
| 665 |
|
|
><P
|
| 666 |
|
|
> This should be a pointer to the appropriate
|
| 667 |
|
|
<SPAN
|
| 668 |
|
|
CLASS="STRUCTNAME"
|
| 669 |
|
|
>usbs_control_endpoint</SPAN
|
| 670 |
|
|
>,
|
| 671 |
|
|
<SPAN
|
| 672 |
|
|
CLASS="STRUCTNAME"
|
| 673 |
|
|
>usbs_rx_endpoint</SPAN
|
| 674 |
|
|
> or
|
| 675 |
|
|
<SPAN
|
| 676 |
|
|
CLASS="STRUCTNAME"
|
| 677 |
|
|
>usbs_tx_endpoint</SPAN
|
| 678 |
|
|
> structure, allowing the
|
| 679 |
|
|
generic testing code to perform low-level I/O.
|
| 680 |
|
|
</P
|
| 681 |
|
|
></DD
|
| 682 |
|
|
><DT
|
| 683 |
|
|
><TT
|
| 684 |
|
|
CLASS="STRUCTFIELD"
|
| 685 |
|
|
><I
|
| 686 |
|
|
>devtab_entry</I
|
| 687 |
|
|
></TT
|
| 688 |
|
|
></DT
|
| 689 |
|
|
><DD
|
| 690 |
|
|
><P
|
| 691 |
|
|
> If the endpoint also has an entry in the system's device table then
|
| 692 |
|
|
this field should give the corresponding string, for example
|
| 693 |
|
|
<TT
|
| 694 |
|
|
CLASS="LITERAL"
|
| 695 |
|
|
>"/dev/usbs1r"</TT
|
| 696 |
|
|
>. This allows the
|
| 697 |
|
|
generic testing code to access the device via higher-level
|
| 698 |
|
|
calls like <TT
|
| 699 |
|
|
CLASS="FUNCTION"
|
| 700 |
|
|
>open</TT
|
| 701 |
|
|
> and <TT
|
| 702 |
|
|
CLASS="FUNCTION"
|
| 703 |
|
|
>read</TT
|
| 704 |
|
|
>.
|
| 705 |
|
|
</P
|
| 706 |
|
|
></DD
|
| 707 |
|
|
><DT
|
| 708 |
|
|
><TT
|
| 709 |
|
|
CLASS="STRUCTFIELD"
|
| 710 |
|
|
><I
|
| 711 |
|
|
>min_size</I
|
| 712 |
|
|
></TT
|
| 713 |
|
|
></DT
|
| 714 |
|
|
><DD
|
| 715 |
|
|
><P
|
| 716 |
|
|
> This indicates the smallest transfer size that the hardware can
|
| 717 |
|
|
support on this endpoint. Typically this will be one.
|
| 718 |
|
|
</P
|
| 719 |
|
|
><DIV
|
| 720 |
|
|
CLASS="NOTE"
|
| 721 |
|
|
><BLOCKQUOTE
|
| 722 |
|
|
CLASS="NOTE"
|
| 723 |
|
|
><P
|
| 724 |
|
|
><B
|
| 725 |
|
|
>Note: </B
|
| 726 |
|
|
> Strictly speaking a minimum size of one is not quite right since it
|
| 727 |
|
|
is valid for a USB transfer to involve zero bytes, in other words a
|
| 728 |
|
|
transfer that involves just headers and acknowledgements and an
|
| 729 |
|
|
empty data phase, and that should be tested as well. However current
|
| 730 |
|
|
device drivers interpret a transfer size of 0 as special, so that
|
| 731 |
|
|
would have to be resolved first.
|
| 732 |
|
|
</P
|
| 733 |
|
|
></BLOCKQUOTE
|
| 734 |
|
|
></DIV
|
| 735 |
|
|
></DD
|
| 736 |
|
|
><DT
|
| 737 |
|
|
><TT
|
| 738 |
|
|
CLASS="STRUCTFIELD"
|
| 739 |
|
|
><I
|
| 740 |
|
|
>max_size</I
|
| 741 |
|
|
></TT
|
| 742 |
|
|
></DT
|
| 743 |
|
|
><DD
|
| 744 |
|
|
><P
|
| 745 |
|
|
> Similarly, this specifies the largest transfer size. For control
|
| 746 |
|
|
endpoints the USB protocol uses only two bytes to hold the transfer
|
| 747 |
|
|
length, so there is an upper bound of 65535 bytes. In practice
|
| 748 |
|
|
it is very unlikely that any control transfers would ever need to
|
| 749 |
|
|
be this large, and in fact such transfers would take a long time
|
| 750 |
|
|
and probably violate timing constraints. For other types of endpoint
|
| 751 |
|
|
any of the protocol, the hardware, or the device driver may impose
|
| 752 |
|
|
size limits. For example a given device driver might be unable to
|
| 753 |
|
|
cope with transfers larger than 65535 bytes. If it should be
|
| 754 |
|
|
possible to transfer arbitrary amounts of data then a value of
|
| 755 |
|
|
<TT
|
| 756 |
|
|
CLASS="LITERAL"
|
| 757 |
|
|
>-1</TT
|
| 758 |
|
|
> indicates no upper limit, and transfer
|
| 759 |
|
|
sizes will be limited by available memory and by the capabilities
|
| 760 |
|
|
of the host machine.
|
| 761 |
|
|
</P
|
| 762 |
|
|
></DD
|
| 763 |
|
|
><DT
|
| 764 |
|
|
><TT
|
| 765 |
|
|
CLASS="STRUCTFIELD"
|
| 766 |
|
|
><I
|
| 767 |
|
|
>max_in_padding</I
|
| 768 |
|
|
></TT
|
| 769 |
|
|
></DT
|
| 770 |
|
|
><DD
|
| 771 |
|
|
><P
|
| 772 |
|
|
> This field is needed on some hardware where it is impossible to
|
| 773 |
|
|
send packets of a certain size. For example the hardware may be
|
| 774 |
|
|
incapable of sending an empty bulk packet to terminate a transfer
|
| 775 |
|
|
that is an exact multiple of the 64-byte bulk packet size.
|
| 776 |
|
|
Instead the driver has to do some padding and send an extra byte,
|
| 777 |
|
|
and the host has to be prepared to receive this extra byte. Such a
|
| 778 |
|
|
driver should specify a value of <TT
|
| 779 |
|
|
CLASS="LITERAL"
|
| 780 |
|
|
>1</TT
|
| 781 |
|
|
> for the
|
| 782 |
|
|
padding field. For most drivers this field should be set to
|
| 783 |
|
|
<TT
|
| 784 |
|
|
CLASS="LITERAL"
|
| 785 |
|
|
>0</TT
|
| 786 |
|
|
>.
|
| 787 |
|
|
</P
|
| 788 |
|
|
><P
|
| 789 |
|
|
> A better solution would be for the device driver to supply a
|
| 790 |
|
|
fragment of Tcl code that would adjust the receive buffer size
|
| 791 |
|
|
only when necessary, rather than for every transfer. Forcing
|
| 792 |
|
|
receive padding on all transfers when only certain transfers
|
| 793 |
|
|
will actually be padded reduces the accuracy of certain tests.
|
| 794 |
|
|
</P
|
| 795 |
|
|
></DD
|
| 796 |
|
|
><DT
|
| 797 |
|
|
><TT
|
| 798 |
|
|
CLASS="STRUCTFIELD"
|
| 799 |
|
|
><I
|
| 800 |
|
|
>alignment</I
|
| 801 |
|
|
></TT
|
| 802 |
|
|
></DT
|
| 803 |
|
|
><DD
|
| 804 |
|
|
><P
|
| 805 |
|
|
> On some hardware data transfers may need to be aligned to certain
|
| 806 |
|
|
boundaries, for example a word boundary or a cacheline boundary.
|
| 807 |
|
|
Although in theory device drivers could hide such alignment
|
| 808 |
|
|
restrictions from higher-level code by having their own buffers and
|
| 809 |
|
|
performing appropriate copying, that would be expensive in terms of
|
| 810 |
|
|
both memory and cpu cycles. Instead the generic testing code will
|
| 811 |
|
|
align any buffers passed to the device driver to the specified
|
| 812 |
|
|
boundary. For example, if the driver requires that buffers be
|
| 813 |
|
|
aligned to a word boundary then it should specify an alignment
|
| 814 |
|
|
value of 4.
|
| 815 |
|
|
</P
|
| 816 |
|
|
></DD
|
| 817 |
|
|
></DL
|
| 818 |
|
|
></DIV
|
| 819 |
|
|
><P
|
| 820 |
|
|
>The device driver should provide an array of these structures
|
| 821 |
|
|
<TT
|
| 822 |
|
|
CLASS="VARNAME"
|
| 823 |
|
|
>usbs_testing_endpoints[]</TT
|
| 824 |
|
|
>. The USB testing code
|
| 825 |
|
|
examines this array and uses the information to perform appropriate
|
| 826 |
|
|
tests. Because different USB devices support different numbers of
|
| 827 |
|
|
endpoints the number of entries in the array is not known in advance,
|
| 828 |
|
|
so instead the testing code looks for a special terminator
|
| 829 |
|
|
<TT
|
| 830 |
|
|
CLASS="VARNAME"
|
| 831 |
|
|
>USBS_TESTING_ENDPOINTS_TERMINATOR</TT
|
| 832 |
|
|
>. An example
|
| 833 |
|
|
array, showing just the control endpoint and the terminator, might
|
| 834 |
|
|
look like this:</P
|
| 835 |
|
|
><TABLE
|
| 836 |
|
|
BORDER="5"
|
| 837 |
|
|
BGCOLOR="#E0E0F0"
|
| 838 |
|
|
WIDTH="70%"
|
| 839 |
|
|
><TR
|
| 840 |
|
|
><TD
|
| 841 |
|
|
><PRE
|
| 842 |
|
|
CLASS="PROGRAMLISTING"
|
| 843 |
|
|
>usbs_testing_endpoint usbs_testing_endpoints[] = {
|
| 844 |
|
|
{
|
| 845 |
|
|
endpoint_type : USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL,
|
| 846 |
|
|
endpoint_number : 0,
|
| 847 |
|
|
endpoint_direction : USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN,
|
| 848 |
|
|
endpoint : (void*) &ep0.common,
|
| 849 |
|
|
devtab_entry : (const char*) 0,
|
| 850 |
|
|
min_size : 1,
|
| 851 |
|
|
max_size : 0x0FFFF,
|
| 852 |
|
|
max_in_padding : 0,
|
| 853 |
|
|
alignment : 0
|
| 854 |
|
|
},
|
| 855 |
|
|
…,
|
| 856 |
|
|
USBS_TESTING_ENDPOINTS_TERMINATOR
|
| 857 |
|
|
};</PRE
|
| 858 |
|
|
></TD
|
| 859 |
|
|
></TR
|
| 860 |
|
|
></TABLE
|
| 861 |
|
|
><DIV
|
| 862 |
|
|
CLASS="NOTE"
|
| 863 |
|
|
><BLOCKQUOTE
|
| 864 |
|
|
CLASS="NOTE"
|
| 865 |
|
|
><P
|
| 866 |
|
|
><B
|
| 867 |
|
|
>Note: </B
|
| 868 |
|
|
>The use of a single array <TT
|
| 869 |
|
|
CLASS="VARNAME"
|
| 870 |
|
|
>usbs_testing_endpoints</TT
|
| 871 |
|
|
>
|
| 872 |
|
|
limits USB testing to platforms with a single USB device: if there
|
| 873 |
|
|
were multiple devices, each defining their own instance of this array,
|
| 874 |
|
|
then there would a collision at link time. In practice this should not
|
| 875 |
|
|
be a major problem since typical USB peripherals only interact with a
|
| 876 |
|
|
single host machine via a single slave port. In addition, even if a
|
| 877 |
|
|
peripheral did have multiple slave ports the current USB testing code
|
| 878 |
|
|
would not support this since it would not know which port to use.</P
|
| 879 |
|
|
></BLOCKQUOTE
|
| 880 |
|
|
></DIV
|
| 881 |
|
|
></DIV
|
| 882 |
|
|
><DIV
|
| 883 |
|
|
CLASS="NAVFOOTER"
|
| 884 |
|
|
><HR
|
| 885 |
|
|
ALIGN="LEFT"
|
| 886 |
|
|
WIDTH="100%"><TABLE
|
| 887 |
|
|
SUMMARY="Footer navigation table"
|
| 888 |
|
|
WIDTH="100%"
|
| 889 |
|
|
BORDER="0"
|
| 890 |
|
|
CELLPADDING="0"
|
| 891 |
|
|
CELLSPACING="0"
|
| 892 |
|
|
><TR
|
| 893 |
|
|
><TD
|
| 894 |
|
|
WIDTH="33%"
|
| 895 |
|
|
ALIGN="left"
|
| 896 |
|
|
VALIGN="top"
|
| 897 |
|
|
><A
|
| 898 |
|
|
HREF="usbs-data.html"
|
| 899 |
|
|
ACCESSKEY="P"
|
| 900 |
|
|
>Prev</A
|
| 901 |
|
|
></TD
|
| 902 |
|
|
><TD
|
| 903 |
|
|
WIDTH="34%"
|
| 904 |
|
|
ALIGN="center"
|
| 905 |
|
|
VALIGN="top"
|
| 906 |
|
|
><A
|
| 907 |
|
|
HREF="ecos-ref.html"
|
| 908 |
|
|
ACCESSKEY="H"
|
| 909 |
|
|
>Home</A
|
| 910 |
|
|
></TD
|
| 911 |
|
|
><TD
|
| 912 |
|
|
WIDTH="33%"
|
| 913 |
|
|
ALIGN="right"
|
| 914 |
|
|
VALIGN="top"
|
| 915 |
|
|
><A
|
| 916 |
|
|
HREF="usbs-testing.html"
|
| 917 |
|
|
ACCESSKEY="N"
|
| 918 |
|
|
>Next</A
|
| 919 |
|
|
></TD
|
| 920 |
|
|
></TR
|
| 921 |
|
|
><TR
|
| 922 |
|
|
><TD
|
| 923 |
|
|
WIDTH="33%"
|
| 924 |
|
|
ALIGN="left"
|
| 925 |
|
|
VALIGN="top"
|
| 926 |
|
|
>Data Endpoints</TD
|
| 927 |
|
|
><TD
|
| 928 |
|
|
WIDTH="34%"
|
| 929 |
|
|
ALIGN="center"
|
| 930 |
|
|
VALIGN="top"
|
| 931 |
|
|
><A
|
| 932 |
|
|
HREF="io-usb-slave.html"
|
| 933 |
|
|
ACCESSKEY="U"
|
| 934 |
|
|
>Up</A
|
| 935 |
|
|
></TD
|
| 936 |
|
|
><TD
|
| 937 |
|
|
WIDTH="33%"
|
| 938 |
|
|
ALIGN="right"
|
| 939 |
|
|
VALIGN="top"
|
| 940 |
|
|
>Testing</TD
|
| 941 |
|
|
></TR
|
| 942 |
|
|
></TABLE
|
| 943 |
|
|
></DIV
|
| 944 |
|
|
></BODY
|
| 945 |
|
|
></HTML
|
| 946 |
|
|
>
|
