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NAME="USBS-WRITING">Writing a USB Device Driver</H1
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NAME="USBS-WRITING">Writing a USB Device Driver</H1
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><DIV
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><DIV
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CLASS="REFNAMEDIV"
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CLASS="REFNAMEDIV"
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><A
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><A
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NAME="AEN16705"
|
NAME="AEN16705"
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></A
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></A
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><H2
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><H2
|
>Name</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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>Writing a USB Device Driver -- USB Device Driver Porting Guide</DIV
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><DIV
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><DIV
|
CLASS="REFSECT1"
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CLASS="REFSECT1"
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><A
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><A
|
NAME="AEN16708"
|
NAME="AEN16708"
|
></A
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></A
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><H2
|
><H2
|
>Introduction</H2
|
>Introduction</H2
|
><P
|
><P
|
>Often the best way to write a USB device driver will be to start with
|
>Often the best way to write a USB device driver will be to start with
|
an existing one and modify it as necessary. The information given here
|
an existing one and modify it as necessary. The information given here
|
is intended primarily as an outline rather than as a complete guide.</P
|
is intended primarily as an outline rather than as a complete guide.</P
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><DIV
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><DIV
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CLASS="NOTE"
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CLASS="NOTE"
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><BLOCKQUOTE
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><BLOCKQUOTE
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CLASS="NOTE"
|
CLASS="NOTE"
|
><P
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><P
|
><B
|
><B
|
>Note: </B
|
>Note: </B
|
>At the time of writing only one USB device driver has been
|
>At the time of writing only one USB device driver has been
|
implemented. Hence it is possible, perhaps probable, that some
|
implemented. Hence it is possible, perhaps probable, that some
|
portability issues have not yet been addressed. One issue
|
portability issues have not yet been addressed. One issue
|
involves the different types of transfer, for example the initial
|
involves the different types of transfer, for example the initial
|
target hardware had no support for isochronous or interrupt transfers,
|
target hardware had no support for isochronous or interrupt transfers,
|
so additional functionality may be needed to switch between transfer
|
so additional functionality may be needed to switch between transfer
|
types. Another issue would be hardware where a given endpoint number,
|
types. Another issue would be hardware where a given endpoint number,
|
say endpoint 1, could be used for either receiving or transmitting
|
say endpoint 1, could be used for either receiving or transmitting
|
data, but not both because a single fifo is used. Issues like these
|
data, but not both because a single fifo is used. Issues like these
|
will have to be resolved as and when additional USB device drivers are
|
will have to be resolved as and when additional USB device drivers are
|
written.</P
|
written.</P
|
></BLOCKQUOTE
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></BLOCKQUOTE
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></DIV
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></DIV
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></DIV
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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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CLASS="REFSECT1"
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><A
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><A
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NAME="AEN16713"
|
NAME="AEN16713"
|
></A
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></A
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><H2
|
><H2
|
>The Control Endpoint</H2
|
>The Control Endpoint</H2
|
><P
|
><P
|
>A USB device driver should provide a single <A
|
>A USB device driver should provide a single <A
|
HREF="usbs-control.html"
|
HREF="usbs-control.html"
|
><SPAN
|
><SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_control_endpoint</SPAN
|
>usbs_control_endpoint</SPAN
|
></A
|
></A
|
>
|
>
|
data structure for every USB device. Typical peripherals will have
|
data structure for every USB device. Typical peripherals will have
|
only one USB port so there will be just one such data structure in the
|
only one USB port so there will be just one such data structure in the
|
entire system, but theoretically it is possible to have multiple USB
|
entire system, but theoretically it is possible to have multiple USB
|
devices. These may all involve the same chip, in which case a single
|
devices. These may all involve the same chip, in which case a single
|
device driver should support multiple device instances, or they may
|
device driver should support multiple device instances, or they may
|
involve different chips. The name or names of these data structures
|
involve different chips. The name or names of these data structures
|
are determined by the device driver, but appropriate care should be
|
are determined by the device driver, but appropriate care should be
|
taken to avoid name clashes. </P
|
taken to avoid name clashes. </P
|
><P
|
><P
|
>A USB device cannot be used unless the control endpoint data structure
|
>A USB device cannot be used unless the control endpoint data structure
|
exists. However, the presence of USB hardware in the target processor
|
exists. However, the presence of USB hardware in the target processor
|
or board does not guarantee that the application will necessarily want
|
or board does not guarantee that the application will necessarily want
|
to use that hardware. To avoid unwanted code or data overheads, the
|
to use that hardware. To avoid unwanted code or data overheads, the
|
device driver can provide a configuration option to determine whether
|
device driver can provide a configuration option to determine whether
|
or not the endpoint 0 data structure is actually provided. A default
|
or not the endpoint 0 data structure is actually provided. A default
|
value of <TT
|
value of <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>CYGINT_IO_USB_SLAVE_CLIENTS</TT
|
>CYGINT_IO_USB_SLAVE_CLIENTS</TT
|
> ensures that
|
> ensures that
|
the USB driver will be enabled automatically if higher-level code does
|
the USB driver will be enabled automatically if higher-level code does
|
require USB support, while leaving ultimate control to the user.</P
|
require USB support, while leaving ultimate control to the user.</P
|
><P
|
><P
|
>The USB device driver is responsible for filling in the
|
>The USB device driver is responsible for filling in the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>start_fn</I
|
>start_fn</I
|
></TT
|
></TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>poll_fn</I
|
>poll_fn</I
|
></TT
|
></TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>interrupt_vector</I
|
>interrupt_vector</I
|
></TT
|
></TT
|
> fields. Usually this can
|
> fields. Usually this can
|
be achieved by static initialization. The driver is also largely
|
be achieved by static initialization. The driver is also largely
|
responsible for maintaining the <TT
|
responsible for maintaining the <TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>state</I
|
>state</I
|
></TT
|
></TT
|
>
|
>
|
field. The <TT
|
field. The <TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>control_buffer</I
|
>control_buffer</I
|
></TT
|
></TT
|
> array should be
|
> array should be
|
used to hold the first packet of a control message. The
|
used to hold the first packet of a control message. The
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>buffer</I
|
>buffer</I
|
></TT
|
></TT
|
> and other fields related to data
|
> and other fields related to data
|
transfers will be managed <A
|
transfers will be managed <A
|
HREF="usbs-control.html#AEN16615"
|
HREF="usbs-control.html#AEN16615"
|
>jointly</A
|
>jointly</A
|
> by higher-level code and
|
> by higher-level code and
|
the device driver. The remaining fields are generally filled in by
|
the device driver. The remaining fields are generally filled in by
|
higher-level code, although the driver should initialize them to NULL
|
higher-level code, although the driver should initialize them to NULL
|
values.</P
|
values.</P
|
><P
|
><P
|
>Hardware permitting, the USB device should be inactive until the
|
>Hardware permitting, the USB device should be inactive until the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>start_fn</I
|
>start_fn</I
|
></TT
|
></TT
|
> is invoked, for example by
|
> is invoked, for example by
|
tristating the appropriate pins. This prevents the host from
|
tristating the appropriate pins. This prevents the host from
|
interacting with the peripheral before all other parts of the system
|
interacting with the peripheral before all other parts of the system
|
have initialized. It is expected that the
|
have initialized. It is expected that the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>start_fn</I
|
>start_fn</I
|
></TT
|
></TT
|
> will only be invoked once, shortly
|
> will only be invoked once, shortly
|
after power-up.</P
|
after power-up.</P
|
><P
|
><P
|
>Where possible the device driver should detect state changes, such as
|
>Where possible the device driver should detect state changes, such as
|
when the connection between host and peripheral is established, and
|
when the connection between host and peripheral is established, and
|
<A
|
<A
|
HREF="usbs-control.html#AEN16552"
|
HREF="usbs-control.html#AEN16552"
|
>report</A
|
>report</A
|
> these to higher-level
|
> these to higher-level
|
code via the <TT
|
code via the <TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>state_change_fn</I
|
>state_change_fn</I
|
></TT
|
></TT
|
> callback, if
|
> callback, if
|
any. The state change to and from configured state cannot easily be
|
any. The state change to and from configured state cannot easily be
|
handled by the device driver itself, instead higher-level code such as
|
handled by the device driver itself, instead higher-level code such as
|
the common USB slave package will take care of this.</P
|
the common USB slave package will take care of this.</P
|
><P
|
><P
|
>Once the connection between host and peripheral has been established,
|
>Once the connection between host and peripheral has been established,
|
the peripheral must be ready to accept control messages at all times,
|
the peripheral must be ready to accept control messages at all times,
|
and must respond to these within certain time constraints. For
|
and must respond to these within certain time constraints. For
|
example, the standard set-address control message must be handled
|
example, the standard set-address control message must be handled
|
within 50ms. The USB specification provides more information on these
|
within 50ms. The USB specification provides more information on these
|
constraints. The device driver is responsible for receiving the
|
constraints. The device driver is responsible for receiving the
|
initial packet of a control message. This packet will always be eight
|
initial packet of a control message. This packet will always be eight
|
bytes and should be stored in the
|
bytes and should be stored in the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>control_buffer</I
|
>control_buffer</I
|
></TT
|
></TT
|
> field. Certain standard
|
> field. Certain standard
|
control messages should be detected and handled by the device driver
|
control messages should be detected and handled by the device driver
|
itself. The most important is set-address, but usually the get-status,
|
itself. The most important is set-address, but usually the get-status,
|
set-feature and clear-feature requests when applied to halted
|
set-feature and clear-feature requests when applied to halted
|
endpoints should also be handled by the driver. Other standard control
|
endpoints should also be handled by the driver. Other standard control
|
messages should first be passed on to the
|
messages should first be passed on to the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>standard_control_fn</I
|
>standard_control_fn</I
|
></TT
|
></TT
|
> callback (if any), and
|
> callback (if any), and
|
finally to the default handler
|
finally to the default handler
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_handle_standard_control</TT
|
>usbs_handle_standard_control</TT
|
> provided by the
|
> provided by the
|
common USB slave package. Class, vendor and reserved control messages
|
common USB slave package. Class, vendor and reserved control messages
|
should always be dispatched to the appropriate callback and there is
|
should always be dispatched to the appropriate callback and there is
|
no default handler for these.</P
|
no default handler for these.</P
|
><P
|
><P
|
>Some control messages will involve further data transfer, not just the
|
>Some control messages will involve further data transfer, not just the
|
initial packet. The device driver must handle this in accordance with
|
initial packet. The device driver must handle this in accordance with
|
the USB specification and the <A
|
the USB specification and the <A
|
HREF="usbs-control.html#AEN16615"
|
HREF="usbs-control.html#AEN16615"
|
>buffer management strategy</A
|
>buffer management strategy</A
|
>. The
|
>. The
|
driver is also responsible for keeping track of whether or not the
|
driver is also responsible for keeping track of whether or not the
|
control operation has succeeded and generating an ACK or STALL
|
control operation has succeeded and generating an ACK or STALL
|
handshake. </P
|
handshake. </P
|
><P
|
><P
|
>The polling support is optional and may not be feasible on all
|
>The polling support is optional and may not be feasible on all
|
hardware. It is only used in certain specialised environments such as
|
hardware. It is only used in certain specialised environments such as
|
RedBoot. A typical implementation of the polling function would just
|
RedBoot. A typical implementation of the polling function would just
|
check whether or not an interrupt would have occurred and, if so, call
|
check whether or not an interrupt would have occurred and, if so, call
|
the same code that the interrupt handler would.</P
|
the same code that the interrupt handler would.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT1"
|
CLASS="REFSECT1"
|
><A
|
><A
|
NAME="AEN16741"
|
NAME="AEN16741"
|
></A
|
></A
|
><H2
|
><H2
|
>Data Endpoints</H2
|
>Data Endpoints</H2
|
><P
|
><P
|
>In addition to the control endpoint data structure, a USB device
|
>In addition to the control endpoint data structure, a USB device
|
driver should also provide appropriate <A
|
driver should also provide appropriate <A
|
HREF="usbs-data.html"
|
HREF="usbs-data.html"
|
>data
|
>data
|
endpoint</A
|
endpoint</A
|
> data structures. Obviously this is only relevant if
|
> data structures. Obviously this is only relevant if
|
the USB support generally is desired, that is if the control endpoint is
|
the USB support generally is desired, that is if the control endpoint is
|
provided. In addition, higher-level code may not require all the
|
provided. In addition, higher-level code may not require all the
|
endpoints, so it may be useful to provide configuration options that
|
endpoints, so it may be useful to provide configuration options that
|
control the presence of each endpoint. For example, the intended
|
control the presence of each endpoint. For example, the intended
|
application might only involve a single transmit endpoint and of
|
application might only involve a single transmit endpoint and of
|
course control messages, so supporting receive endpoints might waste
|
course control messages, so supporting receive endpoints might waste
|
memory.</P
|
memory.</P
|
><P
|
><P
|
>Conceptually, data endpoints are much simpler than the control
|
>Conceptually, data endpoints are much simpler than the control
|
endpoint. The device driver has to supply two functions, one for
|
endpoint. The device driver has to supply two functions, one for
|
data transfers and another to control the halted condition. These
|
data transfers and another to control the halted condition. These
|
implement the functionality for
|
implement the functionality for
|
<A
|
<A
|
HREF="usbs-start-rx.html"
|
HREF="usbs-start-rx.html"
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_rx_buffer</TT
|
>usbs_start_rx_buffer</TT
|
></A
|
></A
|
>,
|
>,
|
<A
|
<A
|
HREF="usbs-start-tx.html"
|
HREF="usbs-start-tx.html"
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
></A
|
></A
|
>,
|
>,
|
<A
|
<A
|
HREF="usbs-halt.html"
|
HREF="usbs-halt.html"
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_set_rx_endpoint_halted</TT
|
>usbs_set_rx_endpoint_halted</TT
|
></A
|
></A
|
> and
|
> and
|
<A
|
<A
|
HREF="usbs-halt.html"
|
HREF="usbs-halt.html"
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_set_tx_endpoint_halted</TT
|
>usbs_set_tx_endpoint_halted</TT
|
></A
|
></A
|
>.
|
>.
|
The device driver is also responsible for maintaining the
|
The device driver is also responsible for maintaining the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>halted</I
|
>halted</I
|
></TT
|
></TT
|
> status.</P
|
> status.</P
|
><P
|
><P
|
>For data transfers, higher-level code will have filled in the
|
>For data transfers, higher-level code will have filled in the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>buffer</I
|
>buffer</I
|
></TT
|
></TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>buffer_size</I
|
>buffer_size</I
|
></TT
|
></TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>complete_fn</I
|
>complete_fn</I
|
></TT
|
></TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>complete_data</I
|
>complete_data</I
|
></TT
|
></TT
|
> fields. The transfer function
|
> fields. The transfer function
|
should arrange for the transfer to start, allowing the host to send or
|
should arrange for the transfer to start, allowing the host to send or
|
receive packets. Typically this will result in an interrupt at the end
|
receive packets. Typically this will result in an interrupt at the end
|
of the transfer or after each packet. Once the entire transfer has
|
of the transfer or after each packet. Once the entire transfer has
|
been completed, the driver's interrupt handling code should invoke the
|
been completed, the driver's interrupt handling code should invoke the
|
completion function. This can happen either in DSR context or thread
|
completion function. This can happen either in DSR context or thread
|
context, depending on the driver's implementation. There are a number
|
context, depending on the driver's implementation. There are a number
|
of special cases to consider. If the endpoint is halted when the
|
of special cases to consider. If the endpoint is halted when the
|
transfer is started then the completion function can be invoked
|
transfer is started then the completion function can be invoked
|
immediately with <TT
|
immediately with <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EAGAIN</TT
|
>-EAGAIN</TT
|
>. If the transfer cannot be
|
>. If the transfer cannot be
|
completed because the connection is broken then the completion
|
completed because the connection is broken then the completion
|
function should be invoked with <TT
|
function should be invoked with <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EPIPE</TT
|
>-EPIPE</TT
|
>. If the
|
>. If the
|
endpoint is stalled during the transfer, either because of a standard
|
endpoint is stalled during the transfer, either because of a standard
|
control message or because higher-level code calls the appropriate
|
control message or because higher-level code calls the appropriate
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>set_halted_fn</I
|
>set_halted_fn</I
|
></TT
|
></TT
|
>, then again the completion
|
>, then again the completion
|
function should be invoked with <TT
|
function should be invoked with <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EAGAIN</TT
|
>-EAGAIN</TT
|
>. Finally,
|
>. Finally,
|
the <<TT
|
the <<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_rx_endpoint_wait</TT
|
>usbs_start_rx_endpoint_wait</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_endpoint_wait</TT
|
>usbs_start_tx_endpoint_wait</TT
|
> functions involve
|
> functions involve
|
calling the device driver's data transfer function with a buffer size
|
calling the device driver's data transfer function with a buffer size
|
of 0 bytes.</P
|
of 0 bytes.</P
|
><DIV
|
><DIV
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><BLOCKQUOTE
|
><BLOCKQUOTE
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><P
|
><P
|
><B
|
><B
|
>Note: </B
|
>Note: </B
|
>Giving a buffer size of 0 bytes a special meaning is problematical
|
>Giving a buffer size of 0 bytes a special meaning is problematical
|
because it prevents transfers of that size. Such transfers are allowed
|
because it prevents transfers of that size. Such transfers are allowed
|
by the USB protocol, consisting of just headers and acknowledgements
|
by the USB protocol, consisting of just headers and acknowledgements
|
and an empty data phase, although rarely useful. A future modification
|
and an empty data phase, although rarely useful. A future modification
|
of the device driver specification will address this issue, although
|
of the device driver specification will address this issue, although
|
care has to be taken that the functionality remains accessible through
|
care has to be taken that the functionality remains accessible through
|
devtab entries as well as via low-level accesses.</P
|
devtab entries as well as via low-level accesses.</P
|
></BLOCKQUOTE
|
></BLOCKQUOTE
|
></DIV
|
></DIV
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT1"
|
CLASS="REFSECT1"
|
><A
|
><A
|
NAME="AEN16768"
|
NAME="AEN16768"
|
></A
|
></A
|
><H2
|
><H2
|
>Devtab Entries</H2
|
>Devtab Entries</H2
|
><P
|
><P
|
>For some applications or higher-level packages it may be more
|
>For some applications or higher-level packages it may be more
|
convenient to use traditional open/read/write I/O calls rather than
|
convenient to use traditional open/read/write I/O calls rather than
|
the non-blocking USB I/O calls. To support this the device driver can
|
the non-blocking USB I/O calls. To support this the device driver can
|
provide a devtab entry for each endpoint, for example:</P
|
provide a devtab entry for each endpoint, for example:</P
|
><TABLE
|
><TABLE
|
BORDER="5"
|
BORDER="5"
|
BGCOLOR="#E0E0F0"
|
BGCOLOR="#E0E0F0"
|
WIDTH="70%"
|
WIDTH="70%"
|
><TR
|
><TR
|
><TD
|
><TD
|
><PRE
|
><PRE
|
CLASS="PROGRAMLISTING"
|
CLASS="PROGRAMLISTING"
|
>#ifdef CYGVAR_DEVS_USB_SA11X0_EP1_DEVTAB_ENTRY
|
>#ifdef CYGVAR_DEVS_USB_SA11X0_EP1_DEVTAB_ENTRY
|
|
|
static CHAR_DEVIO_TABLE(usbs_sa11x0_ep1_devtab_functions,
|
static CHAR_DEVIO_TABLE(usbs_sa11x0_ep1_devtab_functions,
|
&cyg_devio_cwrite,
|
&cyg_devio_cwrite,
|
&usbs_devtab_cread,
|
&usbs_devtab_cread,
|
&cyg_devio_bwrite,
|
&cyg_devio_bwrite,
|
&cyg_devio_bread,
|
&cyg_devio_bread,
|
&cyg_devio_select,
|
&cyg_devio_select,
|
&cyg_devio_get_config,
|
&cyg_devio_get_config,
|
&cyg_devio_set_config);
|
&cyg_devio_set_config);
|
|
|
static CHAR_DEVTAB_ENTRY(usbs_sa11x0_ep1_devtab_entry,
|
static CHAR_DEVTAB_ENTRY(usbs_sa11x0_ep1_devtab_entry,
|
CYGDAT_DEVS_USB_SA11X0_DEVTAB_BASENAME "1r",
|
CYGDAT_DEVS_USB_SA11X0_DEVTAB_BASENAME "1r",
|
0,
|
0,
|
&usbs_sa11x0_ep1_devtab_functions,
|
&usbs_sa11x0_ep1_devtab_functions,
|
&usbs_sa11x0_devtab_dummy_init,
|
&usbs_sa11x0_devtab_dummy_init,
|
0,
|
0,
|
(void*) &usbs_sa11x0_ep1);
|
(void*) &usbs_sa11x0_ep1);
|
#endif</PRE
|
#endif</PRE
|
></TD
|
></TD
|
></TR
|
></TR
|
></TABLE
|
></TABLE
|
><P
|
><P
|
>Again care must be taken to avoid name clashes. This can be achieved
|
>Again care must be taken to avoid name clashes. This can be achieved
|
by having a configuration option to control the base name, with a
|
by having a configuration option to control the base name, with a
|
default value of e.g. <TT
|
default value of e.g. <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>/dev/usbs</TT
|
>/dev/usbs</TT
|
>, and appending an
|
>, and appending an
|
endpoint-specific string. This gives the application developer
|
endpoint-specific string. This gives the application developer
|
sufficient control to eliminate any name clashes. The common USB slave
|
sufficient control to eliminate any name clashes. The common USB slave
|
package provides functions <TT
|
package provides functions <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_devtab_cwrite</TT
|
>usbs_devtab_cwrite</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_devtab_cread</TT
|
>usbs_devtab_cread</TT
|
>, which can be used in the
|
>, which can be used in the
|
function tables for transmit and receive endpoints respectively. The
|
function tables for transmit and receive endpoints respectively. The
|
private field <TT
|
private field <TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>priv</I
|
>priv</I
|
></TT
|
></TT
|
> of the devtab entry
|
> of the devtab entry
|
should be a pointer to the underlying endpoint data structure.</P
|
should be a pointer to the underlying endpoint data structure.</P
|
><P
|
><P
|
>Because devtab entries are never accessed directly, only indirectly,
|
>Because devtab entries are never accessed directly, only indirectly,
|
they would usually be eliminated by the linker. To avoid this the
|
they would usually be eliminated by the linker. To avoid this the
|
devtab entries should normally be defined in a separate source file
|
devtab entries should normally be defined in a separate source file
|
which ends up the special library <TT
|
which ends up the special library <TT
|
CLASS="FILENAME"
|
CLASS="FILENAME"
|
>libextras.a</TT
|
>libextras.a</TT
|
>
|
>
|
rather than in the default library <TT
|
rather than in the default library <TT
|
CLASS="FILENAME"
|
CLASS="FILENAME"
|
>libtarget.a</TT
|
>libtarget.a</TT
|
>.</P
|
>.</P
|
><P
|
><P
|
>Not all applications or higher-level packages will want to use the
|
>Not all applications or higher-level packages will want to use the
|
devtab entries and the blocking I/O facilities. It may be appropriate
|
devtab entries and the blocking I/O facilities. It may be appropriate
|
for the device driver to provide additional configuration options that
|
for the device driver to provide additional configuration options that
|
control whether or not any or all of the devtab entries should be
|
control whether or not any or all of the devtab entries should be
|
provided, to avoid unnecessary memory overheads.</P
|
provided, to avoid unnecessary memory overheads.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT1"
|
CLASS="REFSECT1"
|
><A
|
><A
|
NAME="AEN16781"
|
NAME="AEN16781"
|
></A
|
></A
|
><H2
|
><H2
|
>Interrupt Handling</H2
|
>Interrupt Handling</H2
|
><P
|
><P
|
>A typical USB device driver will need to service interrupts for all of
|
>A typical USB device driver will need to service interrupts for all of
|
the endpoints and possibly for additional USB events such as entering
|
the endpoints and possibly for additional USB events such as entering
|
or leaving suspended mode. Usually these interrupts need not be
|
or leaving suspended mode. Usually these interrupts need not be
|
serviced directly by the ISR. Instead, they can be left to a DSR. If
|
serviced directly by the ISR. Instead, they can be left to a DSR. If
|
the peripheral is not able to accept or send another packet just yet,
|
the peripheral is not able to accept or send another packet just yet,
|
the hardware will generate a NAK and the host will just retry a little
|
the hardware will generate a NAK and the host will just retry a little
|
bit later. If high throughput is required then it may be desirable to
|
bit later. If high throughput is required then it may be desirable to
|
handle the bulk transfer protocol largely at ISR level, that is take
|
handle the bulk transfer protocol largely at ISR level, that is take
|
care of each packet in the ISR and only activate the DSR once the
|
care of each packet in the ISR and only activate the DSR once the
|
whole transfer has completed.</P
|
whole transfer has completed.</P
|
><P
|
><P
|
>Control messages may involve invoking arbitrary callback functions in
|
>Control messages may involve invoking arbitrary callback functions in
|
higher-level code. This should normally happen at DSR level. Doing it
|
higher-level code. This should normally happen at DSR level. Doing it
|
at ISR level could seriously affect the system's interrupt latency and
|
at ISR level could seriously affect the system's interrupt latency and
|
impose unacceptable constraints on what operations can be performed by
|
impose unacceptable constraints on what operations can be performed by
|
those callbacks. If the device driver requires a thread anyway then it
|
those callbacks. If the device driver requires a thread anyway then it
|
may be appropriate to use this thread for invoking the callbacks, but
|
may be appropriate to use this thread for invoking the callbacks, but
|
usually it is not worthwhile to add a new thread to the system just
|
usually it is not worthwhile to add a new thread to the system just
|
for this; higher-level code is expected to write callbacks that
|
for this; higher-level code is expected to write callbacks that
|
function sensibly at DSR level. Much the same applies to the
|
function sensibly at DSR level. Much the same applies to the
|
completion functions associated with data transfers. These should also
|
completion functions associated with data transfers. These should also
|
be invoked at DSR or thread level.</P
|
be invoked at DSR or thread level.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT1"
|
CLASS="REFSECT1"
|
><A
|
><A
|
NAME="AEN16785"
|
NAME="AEN16785"
|
></A
|
></A
|
><H2
|
><H2
|
>Support for USB Testing</H2
|
>Support for USB Testing</H2
|
><P
|
><P
|
>Optionally a USB device driver can provide support for the
|
>Optionally a USB device driver can provide support for the
|
<A
|
<A
|
HREF="usbs-testing.html"
|
HREF="usbs-testing.html"
|
>USB test software</A
|
>USB test software</A
|
>. This requires
|
>. This requires
|
defining a number of additional data structures, allowing the
|
defining a number of additional data structures, allowing the
|
generic test code to work out just what the hardware is capable of and
|
generic test code to work out just what the hardware is capable of and
|
hence what testing can be performed.</P
|
hence what testing can be performed.</P
|
><P
|
><P
|
>The key data structure is
|
>The key data structure is
|
<SPAN
|
<SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_testing_endpoint</SPAN
|
>usbs_testing_endpoint</SPAN
|
>, defined in <TT
|
>, defined in <TT
|
CLASS="FILENAME"
|
CLASS="FILENAME"
|
>cyg/io/usb/usbs.h</TT
|
>cyg/io/usb/usbs.h</TT
|
>. In addition some
|
>. In addition some
|
commonly required constants are provided by the common USB package in
|
commonly required constants are provided by the common USB package in
|
<TT
|
<TT
|
CLASS="FILENAME"
|
CLASS="FILENAME"
|
>cyg/io/usb/usb.h</TT
|
>cyg/io/usb/usb.h</TT
|
>. One
|
>. One
|
<SPAN
|
<SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_testing_endpoint</SPAN
|
>usbs_testing_endpoint</SPAN
|
> structure should be
|
> structure should be
|
defined for each supported endpoint. The following fields need to be
|
defined for each supported endpoint. The following fields need to be
|
filled in:</P
|
filled in:</P
|
><P
|
><P
|
></P
|
></P
|
><DIV
|
><DIV
|
CLASS="VARIABLELIST"
|
CLASS="VARIABLELIST"
|
><DL
|
><DL
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>endpoint_type</I
|
>endpoint_type</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> This specifies the type of endpoint and should be one of
|
> This specifies the type of endpoint and should be one of
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL</TT
|
>USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL</TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>BULK</TT
|
>BULK</TT
|
>, <TT
|
>, <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>ISOCHRONOUS</TT
|
>ISOCHRONOUS</TT
|
> or
|
> or
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>INTERRUPT</TT
|
>INTERRUPT</TT
|
>.
|
>.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>endpoint_number</I
|
>endpoint_number</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> This identifies the number that should be used by the host
|
> This identifies the number that should be used by the host
|
to address this endpoint. For a control endpoint it should
|
to address this endpoint. For a control endpoint it should
|
be 0. For other types of endpoints it should be between
|
be 0. For other types of endpoints it should be between
|
1 and 15.
|
1 and 15.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>endpoint_direction</I
|
>endpoint_direction</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> For control endpoints this field is irrelevant. For other
|
> For control endpoints this field is irrelevant. For other
|
types of endpoint it should be either
|
types of endpoint it should be either
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN</TT
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN</TT
|
> or
|
> or
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_OUT</TT
|
>USB_ENDPOINT_DESCRIPTOR_ENDPOINT_OUT</TT
|
>. If a given
|
>. If a given
|
endpoint number can be used for traffic in both directions then
|
endpoint number can be used for traffic in both directions then
|
there should be two entries in the array, one for each direction.
|
there should be two entries in the array, one for each direction.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>endpoint</I
|
>endpoint</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> This should be a pointer to the appropriate
|
> This should be a pointer to the appropriate
|
<SPAN
|
<SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_control_endpoint</SPAN
|
>usbs_control_endpoint</SPAN
|
>,
|
>,
|
<SPAN
|
<SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_rx_endpoint</SPAN
|
>usbs_rx_endpoint</SPAN
|
> or
|
> or
|
<SPAN
|
<SPAN
|
CLASS="STRUCTNAME"
|
CLASS="STRUCTNAME"
|
>usbs_tx_endpoint</SPAN
|
>usbs_tx_endpoint</SPAN
|
> structure, allowing the
|
> structure, allowing the
|
generic testing code to perform low-level I/O.
|
generic testing code to perform low-level I/O.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>devtab_entry</I
|
>devtab_entry</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> If the endpoint also has an entry in the system's device table then
|
> If the endpoint also has an entry in the system's device table then
|
this field should give the corresponding string, for example
|
this field should give the corresponding string, for example
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>"/dev/usbs1r"</TT
|
>"/dev/usbs1r"</TT
|
>. This allows the
|
>. This allows the
|
generic testing code to access the device via higher-level
|
generic testing code to access the device via higher-level
|
calls like <TT
|
calls like <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>open</TT
|
>open</TT
|
> and <TT
|
> and <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
>.
|
>.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>min_size</I
|
>min_size</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> This indicates the smallest transfer size that the hardware can
|
> This indicates the smallest transfer size that the hardware can
|
support on this endpoint. Typically this will be one.
|
support on this endpoint. Typically this will be one.
|
</P
|
</P
|
><DIV
|
><DIV
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><BLOCKQUOTE
|
><BLOCKQUOTE
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><P
|
><P
|
><B
|
><B
|
>Note: </B
|
>Note: </B
|
> Strictly speaking a minimum size of one is not quite right since it
|
> Strictly speaking a minimum size of one is not quite right since it
|
is valid for a USB transfer to involve zero bytes, in other words a
|
is valid for a USB transfer to involve zero bytes, in other words a
|
transfer that involves just headers and acknowledgements and an
|
transfer that involves just headers and acknowledgements and an
|
empty data phase, and that should be tested as well. However current
|
empty data phase, and that should be tested as well. However current
|
device drivers interpret a transfer size of 0 as special, so that
|
device drivers interpret a transfer size of 0 as special, so that
|
would have to be resolved first.
|
would have to be resolved first.
|
</P
|
</P
|
></BLOCKQUOTE
|
></BLOCKQUOTE
|
></DIV
|
></DIV
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>max_size</I
|
>max_size</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> Similarly, this specifies the largest transfer size. For control
|
> Similarly, this specifies the largest transfer size. For control
|
endpoints the USB protocol uses only two bytes to hold the transfer
|
endpoints the USB protocol uses only two bytes to hold the transfer
|
length, so there is an upper bound of 65535 bytes. In practice
|
length, so there is an upper bound of 65535 bytes. In practice
|
it is very unlikely that any control transfers would ever need to
|
it is very unlikely that any control transfers would ever need to
|
be this large, and in fact such transfers would take a long time
|
be this large, and in fact such transfers would take a long time
|
and probably violate timing constraints. For other types of endpoint
|
and probably violate timing constraints. For other types of endpoint
|
any of the protocol, the hardware, or the device driver may impose
|
any of the protocol, the hardware, or the device driver may impose
|
size limits. For example a given device driver might be unable to
|
size limits. For example a given device driver might be unable to
|
cope with transfers larger than 65535 bytes. If it should be
|
cope with transfers larger than 65535 bytes. If it should be
|
possible to transfer arbitrary amounts of data then a value of
|
possible to transfer arbitrary amounts of data then a value of
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-1</TT
|
>-1</TT
|
> indicates no upper limit, and transfer
|
> indicates no upper limit, and transfer
|
sizes will be limited by available memory and by the capabilities
|
sizes will be limited by available memory and by the capabilities
|
of the host machine.
|
of the host machine.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>max_in_padding</I
|
>max_in_padding</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> This field is needed on some hardware where it is impossible to
|
> This field is needed on some hardware where it is impossible to
|
send packets of a certain size. For example the hardware may be
|
send packets of a certain size. For example the hardware may be
|
incapable of sending an empty bulk packet to terminate a transfer
|
incapable of sending an empty bulk packet to terminate a transfer
|
that is an exact multiple of the 64-byte bulk packet size.
|
that is an exact multiple of the 64-byte bulk packet size.
|
Instead the driver has to do some padding and send an extra byte,
|
Instead the driver has to do some padding and send an extra byte,
|
and the host has to be prepared to receive this extra byte. Such a
|
and the host has to be prepared to receive this extra byte. Such a
|
driver should specify a value of <TT
|
driver should specify a value of <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>1</TT
|
>1</TT
|
> for the
|
> for the
|
padding field. For most drivers this field should be set to
|
padding field. For most drivers this field should be set to
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>0</TT
|
>0</TT
|
>.
|
>.
|
</P
|
</P
|
><P
|
><P
|
> A better solution would be for the device driver to supply a
|
> A better solution would be for the device driver to supply a
|
fragment of Tcl code that would adjust the receive buffer size
|
fragment of Tcl code that would adjust the receive buffer size
|
only when necessary, rather than for every transfer. Forcing
|
only when necessary, rather than for every transfer. Forcing
|
receive padding on all transfers when only certain transfers
|
receive padding on all transfers when only certain transfers
|
will actually be padded reduces the accuracy of certain tests.
|
will actually be padded reduces the accuracy of certain tests.
|
</P
|
</P
|
></DD
|
></DD
|
><DT
|
><DT
|
><TT
|
><TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>alignment</I
|
>alignment</I
|
></TT
|
></TT
|
></DT
|
></DT
|
><DD
|
><DD
|
><P
|
><P
|
> On some hardware data transfers may need to be aligned to certain
|
> On some hardware data transfers may need to be aligned to certain
|
boundaries, for example a word boundary or a cacheline boundary.
|
boundaries, for example a word boundary or a cacheline boundary.
|
Although in theory device drivers could hide such alignment
|
Although in theory device drivers could hide such alignment
|
restrictions from higher-level code by having their own buffers and
|
restrictions from higher-level code by having their own buffers and
|
performing appropriate copying, that would be expensive in terms of
|
performing appropriate copying, that would be expensive in terms of
|
both memory and cpu cycles. Instead the generic testing code will
|
both memory and cpu cycles. Instead the generic testing code will
|
align any buffers passed to the device driver to the specified
|
align any buffers passed to the device driver to the specified
|
boundary. For example, if the driver requires that buffers be
|
boundary. For example, if the driver requires that buffers be
|
aligned to a word boundary then it should specify an alignment
|
aligned to a word boundary then it should specify an alignment
|
value of 4.
|
value of 4.
|
</P
|
</P
|
></DD
|
></DD
|
></DL
|
></DL
|
></DIV
|
></DIV
|
><P
|
><P
|
>The device driver should provide an array of these structures
|
>The device driver should provide an array of these structures
|
<TT
|
<TT
|
CLASS="VARNAME"
|
CLASS="VARNAME"
|
>usbs_testing_endpoints[]</TT
|
>usbs_testing_endpoints[]</TT
|
>. The USB testing code
|
>. The USB testing code
|
examines this array and uses the information to perform appropriate
|
examines this array and uses the information to perform appropriate
|
tests. Because different USB devices support different numbers of
|
tests. Because different USB devices support different numbers of
|
endpoints the number of entries in the array is not known in advance,
|
endpoints the number of entries in the array is not known in advance,
|
so instead the testing code looks for a special terminator
|
so instead the testing code looks for a special terminator
|
<TT
|
<TT
|
CLASS="VARNAME"
|
CLASS="VARNAME"
|
>USBS_TESTING_ENDPOINTS_TERMINATOR</TT
|
>USBS_TESTING_ENDPOINTS_TERMINATOR</TT
|
>. An example
|
>. An example
|
array, showing just the control endpoint and the terminator, might
|
array, showing just the control endpoint and the terminator, might
|
look like this:</P
|
look like this:</P
|
><TABLE
|
><TABLE
|
BORDER="5"
|
BORDER="5"
|
BGCOLOR="#E0E0F0"
|
BGCOLOR="#E0E0F0"
|
WIDTH="70%"
|
WIDTH="70%"
|
><TR
|
><TR
|
><TD
|
><TD
|
><PRE
|
><PRE
|
CLASS="PROGRAMLISTING"
|
CLASS="PROGRAMLISTING"
|
>usbs_testing_endpoint usbs_testing_endpoints[] = {
|
>usbs_testing_endpoint usbs_testing_endpoints[] = {
|
{
|
{
|
endpoint_type : USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL,
|
endpoint_type : USB_ENDPOINT_DESCRIPTOR_ATTR_CONTROL,
|
endpoint_number : 0,
|
endpoint_number : 0,
|
endpoint_direction : USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN,
|
endpoint_direction : USB_ENDPOINT_DESCRIPTOR_ENDPOINT_IN,
|
endpoint : (void*) &ep0.common,
|
endpoint : (void*) &ep0.common,
|
devtab_entry : (const char*) 0,
|
devtab_entry : (const char*) 0,
|
min_size : 1,
|
min_size : 1,
|
max_size : 0x0FFFF,
|
max_size : 0x0FFFF,
|
max_in_padding : 0,
|
max_in_padding : 0,
|
alignment : 0
|
alignment : 0
|
},
|
},
|
…,
|
…,
|
USBS_TESTING_ENDPOINTS_TERMINATOR
|
USBS_TESTING_ENDPOINTS_TERMINATOR
|
};</PRE
|
};</PRE
|
></TD
|
></TD
|
></TR
|
></TR
|
></TABLE
|
></TABLE
|
><DIV
|
><DIV
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><BLOCKQUOTE
|
><BLOCKQUOTE
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><P
|
><P
|
><B
|
><B
|
>Note: </B
|
>Note: </B
|
>The use of a single array <TT
|
>The use of a single array <TT
|
CLASS="VARNAME"
|
CLASS="VARNAME"
|
>usbs_testing_endpoints</TT
|
>usbs_testing_endpoints</TT
|
>
|
>
|
limits USB testing to platforms with a single USB device: if there
|
limits USB testing to platforms with a single USB device: if there
|
were multiple devices, each defining their own instance of this array,
|
were multiple devices, each defining their own instance of this array,
|
then there would a collision at link time. In practice this should not
|
then there would a collision at link time. In practice this should not
|
be a major problem since typical USB peripherals only interact with a
|
be a major problem since typical USB peripherals only interact with a
|
single host machine via a single slave port. In addition, even if a
|
single host machine via a single slave port. In addition, even if a
|
peripheral did have multiple slave ports the current USB testing code
|
peripheral did have multiple slave ports the current USB testing code
|
would not support this since it would not know which port to use.</P
|
would not support this since it would not know which port to use.</P
|
></BLOCKQUOTE
|
></BLOCKQUOTE
|
></DIV
|
></DIV
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
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|
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|
><HR
|
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|
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|
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|
WIDTH="100%"><TABLE
|
WIDTH="100%"><TABLE
|
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|
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><TR
|
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|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="left"
|
ALIGN="left"
|
VALIGN="top"
|
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><A
|
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|
HREF="usbs-data.html"
|
HREF="usbs-data.html"
|
ACCESSKEY="P"
|
ACCESSKEY="P"
|
>Prev</A
|
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ALIGN="center"
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HREF="ecos-ref.html"
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ACCESSKEY="H"
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ALIGN="left"
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>Data Endpoints</TD
|
>Data Endpoints</TD
|
><TD
|
><TD
|
WIDTH="34%"
|
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ALIGN="center"
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>Testing</TD
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