1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>spi_write_then_read</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Linux Device Drivers"><link rel="up" href="spi.html" title="Chapter&#160;9.&#160;Serial Peripheral Interface (SPI)"><link rel="prev" href="API-spi-bus-unlock.html" title="spi_bus_unlock"><link rel="next" href="i2c.html" title="Chapter&#160;10.&#160;I2C and SMBus Subsystem"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">spi_write_then_read</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-spi-bus-unlock.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;9.&#160;Serial Peripheral Interface (SPI)</th><td width="20%" align="right">&#160;<a accesskey="n" href="i2c.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-spi-write-then-read"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>spi_write_then_read &#8212; 
2     SPI synchronous write followed by read
3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">spi_write_then_read </b>(</code></td><td>struct spi_device * <var class="pdparam">spi</var>, </td></tr><tr><td>&#160;</td><td>const void * <var class="pdparam">txbuf</var>, </td></tr><tr><td>&#160;</td><td>unsigned <var class="pdparam">n_tx</var>, </td></tr><tr><td>&#160;</td><td>void * <var class="pdparam">rxbuf</var>, </td></tr><tr><td>&#160;</td><td>unsigned <var class="pdparam">n_rx</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1115211132"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>spi</code></em></span></dt><dd><p>
4     device with which data will be exchanged
5    </p></dd><dt><span class="term"><em class="parameter"><code>txbuf</code></em></span></dt><dd><p>
6     data to be written (need not be dma-safe)
7    </p></dd><dt><span class="term"><em class="parameter"><code>n_tx</code></em></span></dt><dd><p>
8     size of txbuf, in bytes
9    </p></dd><dt><span class="term"><em class="parameter"><code>rxbuf</code></em></span></dt><dd><p>
10     buffer into which data will be read (need not be dma-safe)
11    </p></dd><dt><span class="term"><em class="parameter"><code>n_rx</code></em></span></dt><dd><p>
12     size of rxbuf, in bytes
13    </p></dd></dl></div></div><div class="refsect1"><a name="idp1115216908"></a><h2>Context</h2><p>
14   can sleep
15</p></div><div class="refsect1"><a name="idp1115217524"></a><h2>Description</h2><p>
16   This performs a half duplex MicroWire style transaction with the
17   device, sending txbuf and then reading rxbuf.  The return value
18   is zero for success, else a negative errno status code.
19   This call may only be used from a context that may sleep.
20   </p><p>
21
22   Parameters to this routine are always copied using a small buffer;
23   portable code should never use this for more than 32 bytes.
24   Performance-sensitive or bulk transfer code should instead use
25   spi_{async,sync}() calls with dma-safe buffers.
26</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="API-spi-bus-unlock.html">Prev</a>&#160;</td><td width="20%" align="center"><a accesskey="u" href="spi.html">Up</a></td><td width="40%" align="right">&#160;<a accesskey="n" href="i2c.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="phrase">spi_bus_unlock</span>&#160;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&#160;Chapter&#160;10.&#160;I<sup>2</sup>C and SMBus Subsystem</td></tr></table></div></body></html>
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