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<h1>Synchronous device I/O</h1>
<p>This page documents libusb's synchronous (blocking) API for USB device I/O.
<a href="#_details">More...</a></p>
<table border="0" cellpadding="0" cellspacing="0">
<tr><td colspan="2"><h2>Functions</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__syncio.html#gadb11f7a761bd12fc77a07f4568d56f38">libusb_control_transfer</a> (<a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> *dev_handle, uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex, unsigned char *data, uint16_t wLength, unsigned int timeout)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Perform a USB control transfer. <a href="#gadb11f7a761bd12fc77a07f4568d56f38"></a><br/></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__syncio.html#gab8ae853ab492c22d707241dc26c8a805">libusb_bulk_transfer</a> (struct <a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Perform a USB bulk transfer. <a href="#gab8ae853ab492c22d707241dc26c8a805"></a><br/></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__syncio.html#gac412bda21b7ecf57e4c76877d78e6486">libusb_interrupt_transfer</a> (struct <a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Perform a USB interrupt transfer. <a href="#gac412bda21b7ecf57e4c76877d78e6486"></a><br/></td></tr>
</table>
<hr/><a name="_details"></a><h2>Detailed Description</h2>
<p>This page documents libusb's synchronous (blocking) API for USB device I/O. </p>
<p>This interface is easy to use but has some limitations. More advanced users may wish to consider using the <a class="el" href="group__asyncio.html">asynchronous I/O API</a> instead. </p>
<hr/><h2>Function Documentation</h2>
<a class="anchor" id="gadb11f7a761bd12fc77a07f4568d56f38"></a><!-- doxytag: member="sync.c::libusb_control_transfer" ref="gadb11f7a761bd12fc77a07f4568d56f38" args="(libusb_device_handle *dev_handle, uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex, unsigned char *data, uint16_t wLength, unsigned int timeout)" -->
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<td class="memname">int libusb_control_transfer </td>
<td>(</td>
<td class="paramtype"><a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> * </td>
<td class="paramname"> <em>dev_handle</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint8_t </td>
<td class="paramname"> <em>bmRequestType</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint8_t </td>
<td class="paramname"> <em>bRequest</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint16_t </td>
<td class="paramname"> <em>wValue</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">uint16_t </td>
<td class="paramname"> <em>wIndex</em>, </td>
</tr>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned char * </td>
<td class="paramname"> <em>data</em>, </td>
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<td></td>
<td class="paramtype">uint16_t </td>
<td class="paramname"> <em>wLength</em>, </td>
</tr>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>timeout</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
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<p>Perform a USB control transfer. </p>
<p>The direction of the transfer is inferred from the bmRequestType field of the setup packet.</p>
<p>The wValue, wIndex and wLength fields values should be given in host-endian byte order.</p>
<dl><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>dev_handle</em> </td><td>a handle for the device to communicate with </td></tr>
<tr><td valign="top"></td><td valign="top"><em>bmRequestType</em> </td><td>the request type field for the setup packet </td></tr>
<tr><td valign="top"></td><td valign="top"><em>bRequest</em> </td><td>the request field for the setup packet </td></tr>
<tr><td valign="top"></td><td valign="top"><em>wValue</em> </td><td>the value field for the setup packet </td></tr>
<tr><td valign="top"></td><td valign="top"><em>wIndex</em> </td><td>the index field for the setup packet </td></tr>
<tr><td valign="top"></td><td valign="top"><em>data</em> </td><td>a suitably-sized data buffer for either input or output (depending on direction bits within bmRequestType) </td></tr>
<tr><td valign="top"></td><td valign="top"><em>wLength</em> </td><td>the length field for the setup packet. The data buffer should be at least this size. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>timeout</em> </td><td>timeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0. </td></tr>
</table>
</dd>
</dl>
<dl class="return"><dt><b>Returns:</b></dt><dd>on success, the number of bytes actually transferred </dd>
<dd>
LIBUSB_ERROR_TIMEOUT if the transfer timed out </dd>
<dd>
LIBUSB_ERROR_PIPE if the control request was not supported by the device </dd>
<dd>
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected </dd>
<dd>
another LIBUSB_ERROR code on other failures </dd></dl>
</div>
</div>
<a class="anchor" id="gab8ae853ab492c22d707241dc26c8a805"></a><!-- doxytag: member="sync.c::libusb_bulk_transfer" ref="gab8ae853ab492c22d707241dc26c8a805" args="(struct libusb_device_handle *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)" -->
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<td class="memname">int libusb_bulk_transfer </td>
<td>(</td>
<td class="paramtype">struct <a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> * </td>
<td class="paramname"> <em>dev_handle</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned char </td>
<td class="paramname"> <em>endpoint</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned char * </td>
<td class="paramname"> <em>data</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>length</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int * </td>
<td class="paramname"> <em>transferred</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>timeout</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
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<div class="memdoc">
<p>Perform a USB bulk transfer. </p>
<p>The direction of the transfer is inferred from the direction bits of the endpoint address.</p>
<p>For bulk reads, the <code>length</code> field indicates the maximum length of data you are expecting to receive. If less data arrives than expected, this function will return that data, so be sure to check the <code>transferred</code> output parameter.</p>
<p>You should also check the <code>transferred</code> parameter for bulk writes. Not all of the data may have been written.</p>
<p>Also check <code>transferred</code> when dealing with a timeout error code. libusb may have to split your transfer into a number of chunks to satisfy underlying O/S requirements, meaning that the timeout may expire after the first few chunks have completed. libusb is careful not to lose any data that may have been transferred; do not assume that timeout conditions indicate a complete lack of I/O.</p>
<dl><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>dev_handle</em> </td><td>a handle for the device to communicate with </td></tr>
<tr><td valign="top"></td><td valign="top"><em>endpoint</em> </td><td>the address of a valid endpoint to communicate with </td></tr>
<tr><td valign="top"></td><td valign="top"><em>data</em> </td><td>a suitably-sized data buffer for either input or output (depending on endpoint) </td></tr>
<tr><td valign="top"></td><td valign="top"><em>length</em> </td><td>for bulk writes, the number of bytes from data to be sent. for bulk reads, the maximum number of bytes to receive into the data buffer. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>transferred</em> </td><td>output location for the number of bytes actually transferred. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>timeout</em> </td><td>timeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0.</td></tr>
</table>
</dd>
</dl>
<dl class="return"><dt><b>Returns:</b></dt><dd>0 on success (and populates <code>transferred</code>) </dd>
<dd>
LIBUSB_ERROR_TIMEOUT if the transfer timed out (and populates <code>transferred</code>) </dd>
<dd>
LIBUSB_ERROR_PIPE if the endpoint halted </dd>
<dd>
LIBUSB_ERROR_OVERFLOW if the device offered more data, see <a class="el" href="packetoverflow.html">Packets and overflows</a> </dd>
<dd>
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected </dd>
<dd>
another LIBUSB_ERROR code on other failures </dd></dl>
</div>
</div>
<a class="anchor" id="gac412bda21b7ecf57e4c76877d78e6486"></a><!-- doxytag: member="sync.c::libusb_interrupt_transfer" ref="gac412bda21b7ecf57e4c76877d78e6486" args="(struct libusb_device_handle *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)" -->
<div class="memitem">
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<td class="memname">int libusb_interrupt_transfer </td>
<td>(</td>
<td class="paramtype">struct <a class="el" href="group__dev.html#ga7df95821d20d27b5597f1d783749d6a4">libusb_device_handle</a> * </td>
<td class="paramname"> <em>dev_handle</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned char </td>
<td class="paramname"> <em>endpoint</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned char * </td>
<td class="paramname"> <em>data</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>length</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int * </td>
<td class="paramname"> <em>transferred</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>timeout</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>Perform a USB interrupt transfer. </p>
<p>The direction of the transfer is inferred from the direction bits of the endpoint address.</p>
<p>For interrupt reads, the <code>length</code> field indicates the maximum length of data you are expecting to receive. If less data arrives than expected, this function will return that data, so be sure to check the <code>transferred</code> output parameter.</p>
<p>You should also check the <code>transferred</code> parameter for interrupt writes. Not all of the data may have been written.</p>
<p>Also check <code>transferred</code> when dealing with a timeout error code. libusb may have to split your transfer into a number of chunks to satisfy underlying O/S requirements, meaning that the timeout may expire after the first few chunks have completed. libusb is careful not to lose any data that may have been transferred; do not assume that timeout conditions indicate a complete lack of I/O.</p>
<p>The default endpoint bInterval value is used as the polling interval.</p>
<dl><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>dev_handle</em> </td><td>a handle for the device to communicate with </td></tr>
<tr><td valign="top"></td><td valign="top"><em>endpoint</em> </td><td>the address of a valid endpoint to communicate with </td></tr>
<tr><td valign="top"></td><td valign="top"><em>data</em> </td><td>a suitably-sized data buffer for either input or output (depending on endpoint) </td></tr>
<tr><td valign="top"></td><td valign="top"><em>length</em> </td><td>for bulk writes, the number of bytes from data to be sent. for bulk reads, the maximum number of bytes to receive into the data buffer. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>transferred</em> </td><td>output location for the number of bytes actually transferred. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>timeout</em> </td><td>timeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0.</td></tr>
</table>
</dd>
</dl>
<dl class="return"><dt><b>Returns:</b></dt><dd>0 on success (and populates <code>transferred</code>) </dd>
<dd>
LIBUSB_ERROR_TIMEOUT if the transfer timed out </dd>
<dd>
LIBUSB_ERROR_PIPE if the endpoint halted </dd>
<dd>
LIBUSB_ERROR_OVERFLOW if the device offered more data, see <a class="el" href="packetoverflow.html">Packets and overflows</a> </dd>
<dd>
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected </dd>
<dd>
another LIBUSB_ERROR code on other error </dd></dl>
</div>
</div>
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