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><A
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><A
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NAME="USBS-START-TX"
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NAME="USBS-START-TX"
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>Sending Data to the Host</A
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>Sending Data to the Host</A
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></H1
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></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="AEN349"
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NAME="AEN349"
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></A
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></A
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><H2
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><H2
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>Name</H2
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>Name</H2
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><TT
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><TT
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CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
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>usbs_start_tx_buffer</TT
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> -- Sending Data to the Host</DIV
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> -- Sending Data to the Host</DIV
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><DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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CLASS="REFSYNOPSISDIV"
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><A
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><A
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NAME="AEN353"
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NAME="AEN353"
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></A
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></A
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><H2
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><H2
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>Synopsis</H2
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>Synopsis</H2
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><DIV
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><DIV
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CLASS="FUNCSYNOPSIS"
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CLASS="FUNCSYNOPSIS"
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><A
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><A
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NAME="AEN354"
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NAME="AEN354"
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></A
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></A
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><P
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><P
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></P
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></P
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><TABLE
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><TABLE
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BORDER="0"
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><TR
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><TD
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><TD
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><PRE
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><PRE
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CLASS="FUNCSYNOPSISINFO"
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CLASS="FUNCSYNOPSISINFO"
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>#include <cyg/io/usb/usbs.h></PRE
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>#include <cyg/io/usb/usbs.h></PRE
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></TD
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></TD
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></TR
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></TR
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></TABLE
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></TABLE
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><P
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><P
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><CODE
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><CODE
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><CODE
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><CODE
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CLASS="FUNCDEF"
|
CLASS="FUNCDEF"
|
>void usbs_start_tx_buffer</CODE
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>void usbs_start_tx_buffer</CODE
|
>(usbs_tx_endpoint* ep, const unsigned char* buffer, int length, void (*)(void*,int) complete_fn, void * complete_data);</CODE
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>(usbs_tx_endpoint* ep, const unsigned char* buffer, int length, void (*)(void*,int) complete_fn, void * complete_data);</CODE
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></P
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></P
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><P
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><P
|
><CODE
|
><CODE
|
><CODE
|
><CODE
|
CLASS="FUNCDEF"
|
CLASS="FUNCDEF"
|
>void usbs_start_tx</CODE
|
>void usbs_start_tx</CODE
|
>(usbs_tx_endpoint* ep);</CODE
|
>(usbs_tx_endpoint* ep);</CODE
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></P
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></P
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><P
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><P
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></P
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></P
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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="AEN374"
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NAME="AEN374"
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></A
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></A
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><H2
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><H2
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><TT
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><TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
|
>Description</TT
|
>Description</TT
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></H2
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></H2
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><P
|
><P
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> is a USB-specific function
|
> is a USB-specific function
|
to transfer data from peripheral to host. It can be used for bulk,
|
to transfer data from peripheral to host. It can be used for bulk,
|
interrupt or isochronous transfers, but not for control messages;
|
interrupt or isochronous transfers, but not for control messages;
|
instead those involve manipulating the <A
|
instead those involve manipulating the <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 directly. The function takes five arguments:</P
|
data structure directly. The function takes five arguments:</P
|
><P
|
><P
|
></P
|
></P
|
><OL
|
><OL
|
TYPE="1"
|
TYPE="1"
|
><LI
|
><LI
|
><P
|
><P
|
>The first argument identifies the specific endpoint that should be
|
>The first argument identifies the specific endpoint that should be
|
used. Different USB devices will support different sets of endpoints
|
used. Different USB devices will support different sets of endpoints
|
and the device driver will provide appropriate data structures. The
|
and the device driver will provide appropriate data structures. The
|
device driver's documentation should be consulted for details of which
|
device driver's documentation should be consulted for details of which
|
endpoints are available.</P
|
endpoints are available.</P
|
></LI
|
></LI
|
><LI
|
><LI
|
><P
|
><P
|
>The <TT
|
>The <TT
|
CLASS="PARAMETER"
|
CLASS="PARAMETER"
|
><I
|
><I
|
>buffer</I
|
>buffer</I
|
></TT
|
></TT
|
> and <TT
|
> and <TT
|
CLASS="PARAMETER"
|
CLASS="PARAMETER"
|
><I
|
><I
|
>length</I
|
>length</I
|
></TT
|
></TT
|
>
|
>
|
arguments control the actual transfer. USB device drivers are not
|
arguments control the actual transfer. USB device drivers are not
|
allowed to modify the buffer during the transfer, so the data can
|
allowed to modify the buffer during the transfer, so the data can
|
reside in read-only memory. The transfer will be for all the data
|
reside in read-only memory. The transfer will be for all the data
|
specified, and it is the responsibility of higher-level code to make
|
specified, and it is the responsibility of higher-level code to make
|
sure that the host is expecting this amount of data. For isochronous
|
sure that the host is expecting this amount of data. For isochronous
|
transfers the USB specification imposes an upper bound of 1023 bytes,
|
transfers the USB specification imposes an upper bound of 1023 bytes,
|
but a smaller limit may be set in the <A
|
but a smaller limit may be set in the <A
|
HREF="usbs-enum.html#AEN142"
|
HREF="usbs-enum.html#AEN142"
|
>enumeration data</A
|
>enumeration data</A
|
>. Interrupt
|
>. Interrupt
|
transfers have an upper bound of 64 bytes or less, as per the
|
transfers have an upper bound of 64 bytes or less, as per the
|
enumeration data. Bulk transfers are more complicated because they can
|
enumeration data. Bulk transfers are more complicated because they can
|
involve multiple 64-byte packets plus a terminating packet of less
|
involve multiple 64-byte packets plus a terminating packet of less
|
than 64 bytes, so the basic USB specification does not impose an upper
|
than 64 bytes, so the basic USB specification does not impose an upper
|
limit on the total transfer size. Instead it is left to higher-level
|
limit on the total transfer size. Instead it is left to higher-level
|
protocols to specify an appropriate upper bound. If the peripheral
|
protocols to specify an appropriate upper bound. If the peripheral
|
attempts to send more data than the host is willing to accept then the
|
attempts to send more data than the host is willing to accept then the
|
resulting behaviour is undefined and may well depend on the specific
|
resulting behaviour is undefined and may well depend on the specific
|
host operating system being used.</P
|
host operating system being used.</P
|
><P
|
><P
|
>For bulk transfers, the USB device driver or the underlying hardware
|
>For bulk transfers, the USB device driver or the underlying hardware
|
will automatically split the transfer up into the appropriate number
|
will automatically split the transfer up into the appropriate number
|
of full-size 64-byte packets plus a single terminating packet, which
|
of full-size 64-byte packets plus a single terminating packet, which
|
may be 0 bytes.</P
|
may be 0 bytes.</P
|
></LI
|
></LI
|
><LI
|
><LI
|
><P
|
><P
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> is non-blocking. It merely
|
> is non-blocking. It merely
|
starts the transmit operation, and does not wait for completion. At
|
starts the transmit operation, and does not wait for completion. At
|
some later point the USB device driver will invoke the completion
|
some later point the USB device driver will invoke the completion
|
function parameter with two arguments: the completion data defined by
|
function parameter with two arguments: the completion data defined by
|
the last parameter, and a result field. This result will be either an
|
the last parameter, and a result field. This result will be either an
|
error code < <TT
|
error code < <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>0</TT
|
>0</TT
|
>, or the amount of data
|
>, or the amount of data
|
transferred which should correspond to the
|
transferred which should correspond to the
|
<TT
|
<TT
|
CLASS="PARAMETER"
|
CLASS="PARAMETER"
|
><I
|
><I
|
>length</I
|
>length</I
|
></TT
|
></TT
|
> argument. The most likely errors are
|
> argument. The most likely errors are
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EPIPE</TT
|
>-EPIPE</TT
|
> to indicate that the connection between the
|
> to indicate that the connection between the
|
host and the target has been broken, and <TT
|
host and the target has been broken, and <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EAGAIN</TT
|
>-EAGAIN</TT
|
>
|
>
|
for when the endpoint has been <A
|
for when the endpoint has been <A
|
HREF="usbs-halt.html"
|
HREF="usbs-halt.html"
|
>halted</A
|
>halted</A
|
>. Specific USB device drivers may
|
>. Specific USB device drivers may
|
define additional error conditions.</P
|
define additional error conditions.</P
|
></LI
|
></LI
|
></OL
|
></OL
|
><P
|
><P
|
>The normal sequence of events is that the USB device driver will
|
>The normal sequence of events is that the USB device driver will
|
update the appropriate hardware registers. At some point after that
|
update the appropriate hardware registers. At some point after that
|
the host will attempt to fetch data by transmitting an IN token. Since
|
the host will attempt to fetch data by transmitting an IN token. Since
|
a transmit operation is now in progress the peripheral can send a
|
a transmit operation is now in progress the peripheral can send a
|
packet of data, and the host will generate an ACK. At this point the
|
packet of data, and the host will generate an ACK. At this point the
|
USB hardware will generate an interrupt, and the device driver will
|
USB hardware will generate an interrupt, and the device driver will
|
service this interrupt and arrange for a DSR to be called. Isochronous
|
service this interrupt and arrange for a DSR to be called. Isochronous
|
and interrupt transfers involve just a single packet. However, bulk
|
and interrupt transfers involve just a single packet. However, bulk
|
transfers may involve multiple packets so the device driver has to
|
transfers may involve multiple packets so the device driver has to
|
check whether there is more data to send and set things up for the
|
check whether there is more data to send and set things up for the
|
next packet. When the device driver DSR detects a complete transfer it
|
next packet. When the device driver DSR detects a complete transfer it
|
will inform higher-level code by invoking the supplied completion
|
will inform higher-level code by invoking the supplied completion
|
function.</P
|
function.</P
|
><P
|
><P
|
>This means that the completion function will normally be invoked by a
|
>This means that the completion function will normally be invoked by a
|
DSR and not in thread context - although some USB device drivers may
|
DSR and not in thread context - although some USB device drivers may
|
have a different implementation. Therefore the completion function is
|
have a different implementation. Therefore the completion function is
|
restricted in what it can do, in particular it must not make any
|
restricted in what it can do, in particular it must not make any
|
calls that will or may block such as locking a mutex or allocating
|
calls that will or may block such as locking a mutex or allocating
|
memory. The kernel documentation should be consulted for more details
|
memory. The kernel documentation should be consulted for more details
|
of DSR's and interrupt handling generally.</P
|
of DSR's and interrupt handling generally.</P
|
><P
|
><P
|
>It is possible that the completion function will be invoked before
|
>It is possible that the completion function will be invoked before
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> returns. Such an event would
|
> returns. Such an event would
|
be unusual because the transfer cannot happen until the next time the
|
be unusual because the transfer cannot happen until the next time the
|
host tries to fetch data from this peripheral, but it may happen if,
|
host tries to fetch data from this peripheral, but it may happen if,
|
for example, another interrupt happens and a higher priority thread is
|
for example, another interrupt happens and a higher priority thread is
|
scheduled to run. Also, if the endpoint is currently halted then the
|
scheduled to run. Also, if the endpoint is currently halted then the
|
completion function will be invoked immediately with
|
completion function will be invoked immediately with
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>-EAGAIN</TT
|
>-EAGAIN</TT
|
>: typically this will happen in the current
|
>: typically this will happen in the current
|
thread rather than in a separate DSR. The completion function is
|
thread rather than in a separate DSR. The completion function is
|
allowed to start another transfer immediately by calling
|
allowed to start another transfer immediately by calling
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> again.</P
|
> again.</P
|
><P
|
><P
|
>USB device drivers are not expected to perform any locking. It is the
|
>USB device drivers are not expected to perform any locking. It is the
|
responsibility of higher-level code to ensure that there is only one
|
responsibility of higher-level code to ensure that there is only one
|
transmit operation for a given endpoint in progress at any one time.
|
transmit operation for a given endpoint in progress at any one time.
|
If there are concurrent calls to
|
If there are concurrent calls to
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> then the resulting behaviour
|
> then the resulting behaviour
|
is undefined. For typical USB applications this does not present any
|
is undefined. For typical USB applications this does not present any
|
problems because only piece of code will access a given endpoint at
|
problems because only piece of code will access a given endpoint at
|
any particular time.</P
|
any particular time.</P
|
><P
|
><P
|
>The following code fragment illustrates a very simple use of
|
>The following code fragment illustrates a very simple use of
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx_buffer</TT
|
>usbs_start_tx_buffer</TT
|
> to implement a blocking
|
> to implement a blocking
|
transmit, using a semaphore to synchronise between the foreground
|
transmit, using a semaphore to synchronise between the foreground
|
thread and the DSR. For a simple example like this no completion data
|
thread and the DSR. For a simple example like this no completion data
|
is needed.</P
|
is needed.</P
|
><TABLE
|
><TABLE
|
BORDER="0"
|
BORDER="0"
|
BGCOLOR="#E0E0E0"
|
BGCOLOR="#E0E0E0"
|
WIDTH="100%"
|
WIDTH="100%"
|
><TR
|
><TR
|
><TD
|
><TD
|
><PRE
|
><PRE
|
CLASS="PROGRAMLISTING"
|
CLASS="PROGRAMLISTING"
|
>static int error_code = 0;
|
>static int error_code = 0;
|
static cyg_sem_t completion_wait;
|
static cyg_sem_t completion_wait;
|
|
|
static void
|
static void
|
completion_fn(void* data, int result)
|
completion_fn(void* data, int result)
|
{
|
{
|
error_code = result;
|
error_code = result;
|
cyg_semaphore_post(&completion_wait);
|
cyg_semaphore_post(&completion_wait);
|
}
|
}
|
|
|
int
|
int
|
blocking_transmit(usbs_tx_endpoint* ep, const unsigned char* buf, int len)
|
blocking_transmit(usbs_tx_endpoint* ep, const unsigned char* buf, int len)
|
{
|
{
|
error_code = 0;
|
error_code = 0;
|
usbs_start_tx_buffer(ep, buf, len, &completion_fn, NULL);
|
usbs_start_tx_buffer(ep, buf, len, &completion_fn, NULL);
|
cyg_semaphore_wait(&completion_wait);
|
cyg_semaphore_wait(&completion_wait);
|
return error_code;
|
return error_code;
|
}</PRE
|
}</PRE
|
></TD
|
></TD
|
></TR
|
></TR
|
></TABLE
|
></TABLE
|
><P
|
><P
|
>There is also a utility function <TT
|
>There is also a utility function <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start</TT
|
>usbs_start</TT
|
>. This
|
>. This
|
can be used by code that wants to manipulate <A
|
can be used by code that wants to manipulate <A
|
HREF="usbs-data.html"
|
HREF="usbs-data.html"
|
>data endpoints</A
|
>data endpoints</A
|
> directly, specifically the
|
> directly, specifically the
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>complete_fn</I
|
>complete_fn</I
|
></TT
|
></TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>complete_data</I
|
>complete_data</I
|
></TT
|
></TT
|
>,
|
>,
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>buffer</I
|
>buffer</I
|
></TT
|
></TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="STRUCTFIELD"
|
CLASS="STRUCTFIELD"
|
><I
|
><I
|
>buffer_size</I
|
>buffer_size</I
|
></TT
|
></TT
|
> fields.
|
> fields.
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_tx</TT
|
>usbs_start_tx</TT
|
> just calls a function supplied by
|
> just calls a function supplied by
|
the device driver.</P
|
the device driver.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="NAVFOOTER"
|
CLASS="NAVFOOTER"
|
><HR
|
><HR
|
ALIGN="LEFT"
|
ALIGN="LEFT"
|
WIDTH="100%"><TABLE
|
WIDTH="100%"><TABLE
|
WIDTH="100%"
|
WIDTH="100%"
|
BORDER="0"
|
BORDER="0"
|
CELLPADDING="0"
|
CELLPADDING="0"
|
CELLSPACING="0"
|
CELLSPACING="0"
|
><TR
|
><TR
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="left"
|
ALIGN="left"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="usbs-start-rx.html"
|
HREF="usbs-start-rx.html"
|
>Prev</A
|
>Prev</A
|
></TD
|
></TD
|
><TD
|
><TD
|
WIDTH="34%"
|
WIDTH="34%"
|
ALIGN="center"
|
ALIGN="center"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="io-usb-slave.html"
|
HREF="io-usb-slave.html"
|
>Home</A
|
>Home</A
|
></TD
|
></TD
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="right"
|
ALIGN="right"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="usbs-halt.html"
|
HREF="usbs-halt.html"
|
>Next</A
|
>Next</A
|
></TD
|
></TD
|
></TR
|
></TR
|
><TR
|
><TR
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="left"
|
ALIGN="left"
|
VALIGN="top"
|
VALIGN="top"
|
>Receiving Data from the Host</TD
|
>Receiving Data from the Host</TD
|
><TD
|
><TD
|
WIDTH="34%"
|
WIDTH="34%"
|
ALIGN="center"
|
ALIGN="center"
|
VALIGN="top"
|
VALIGN="top"
|
> </TD
|
> </TD
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="right"
|
ALIGN="right"
|
VALIGN="top"
|
VALIGN="top"
|
>Halted Endpoints</TD
|
>Halted Endpoints</TD
|
></TR
|
></TR
|
></TABLE
|
></TABLE
|
></DIV
|
></DIV
|
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