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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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>User API</TITLE
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TITLE="I/O Package (Device Drivers)"
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TITLE="Introduction"
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TITLE="Serial driver details"
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>eCos Reference Manual</TH
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><A
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>Prev</A
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="IO-USER-API">Chapter 15. User API</H1
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><P
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>All functions, except <TT
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CLASS="FUNCTION"
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>cyg_io_lookup()</TT
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>
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require an I/O &#8220;handle&#8221;.</P
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><P
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>All functions return a value of the type <SPAN
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CLASS="TYPE"
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>Cyg_ErrNo</SPAN
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>. If an
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error condition is detected, this value will be negative and the
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absolute value indicates the actual error, as specified in
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<TT
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CLASS="FILENAME"
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>cyg/error/codes.h</TT
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>. The only other legal return
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value will be <TT
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CLASS="VARNAME"
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>ENOERR</TT
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>. All other function arguments
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are pointers (references). This allows the drivers to pass information
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efficiently, both into and out of the driver. The most striking
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example of this is the &#8220;length&#8221; value passed to the read
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and write functions. This parameter contains the desired length of
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data on input to the function and the actual transferred length on
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return.</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>// Lookup a device and return its handle
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  Cyg_ErrNo <TT
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CLASS="FUNCTION"
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>cyg_io_lookup</TT
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>(
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    const char <TT
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CLASS="PARAMETER"
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><I
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>*name</I
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></TT
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>,
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    cyg_io_handle_t <TT
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CLASS="PARAMETER"
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><I
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>*handle</I
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></TT
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> )</PRE
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></TD
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></TR
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></TABLE
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><P
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>This function maps a device name onto an appropriate handle. If the
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named device is not in the system, then the error
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<TT
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CLASS="VARNAME"
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>-ENOENT</TT
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> is returned. If the device is found, then
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the handle for the device is returned by way of the handle pointer
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<TT
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CLASS="PARAMETER"
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><I
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>*handle</I
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></TT
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>.</P
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><TABLE
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>// Write data to a device
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Cyg_ErrNo <TT
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CLASS="FUNCTION"
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>cyg_io_write</TT
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>(
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    cyg_io_handle_t <TT
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CLASS="PARAMETER"
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><I
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>handle</I
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></TT
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>,
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    const void <TT
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CLASS="PARAMETER"
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><I
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>*buf</I
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></TT
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>,
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    cyg_uint32 <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> )</PRE
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></TD
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></TR
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></TABLE
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><P
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>This function sends data to a device. The size of data to send is
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contained in <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> and the actual size sent will
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be returned in the same place.</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>// Read data from a device
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Cyg_ErrNo <TT
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CLASS="FUNCTION"
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>cyg_io_read</TT
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>(
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    cyg_io_handle_t <TT
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CLASS="PARAMETER"
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><I
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>handle</I
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></TT
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>,
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    void <TT
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CLASS="PARAMETER"
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><I
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>*buf</I
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></TT
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>,
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    cyg_uint32 <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> )</PRE
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></TD
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></TR
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></TABLE
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><P
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>This function receives data from a device. The desired size of data to
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receive is contained in <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> and the actual
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size obtained will be returned in the same place.</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>// Get the configuration of a device
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Cyg_ErrNo <TT
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CLASS="FUNCTION"
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>cyg_io_get_config</TT
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>(
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    cyg_io_handle_t <TT
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CLASS="PARAMETER"
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><I
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>handle</I
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></TT
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>,
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    cyg_uint32 <TT
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CLASS="PARAMETER"
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><I
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>key</I
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></TT
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>,
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    void *<TT
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CLASS="PARAMETER"
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><I
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>buf</I
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></TT
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>,
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    cyg_uint32 *<TT
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CLASS="PARAMETER"
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><I
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>len</I
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></TT
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> )</PRE
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></TD
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></TR
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></TABLE
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><P
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>This function is used to obtain run-time configuration about a
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device. The type of information retrieved is specified by the
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<TT
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CLASS="PARAMETER"
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><I
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>key</I
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></TT
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>. The data will be returned in the given
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buffer. The value of <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> should contain the
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amount of data requested, which must be at least as large as the size
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appropriate to the selected key. The actual size of data retrieved is
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placed in <TT
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CLASS="PARAMETER"
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><I
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> *len</I
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></TT
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>. The appropriate key values
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differ for each driver and are all listed in the file
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<TT
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CLASS="FILENAME"
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>&lt;cyg/io/config_keys.h&gt;</TT
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>.</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>// Change the configuration of a device
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Cyg_ErrNo <TT
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CLASS="FUNCTION"
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>cyg_io_set_config</TT
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>(
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    cyg_io_handle_t <TT
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CLASS="PARAMETER"
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><I
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>handle</I
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></TT
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>,
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    cyg_uint32 <TT
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CLASS="PARAMETER"
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><I
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>key</I
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></TT
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>,
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    const void <TT
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CLASS="PARAMETER"
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><I
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>*buf</I
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></TT
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>,
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    cyg_uint32 <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> )</PRE
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></TD
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></TR
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></TABLE
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><P
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>This function is used to manipulate or change the run-time
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configuration of a device. The type of information is specified by the
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<TT
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CLASS="PARAMETER"
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><I
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>key</I
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></TT
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>. The data will be obtained from the given
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buffer. The value of <TT
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CLASS="PARAMETER"
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><I
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>*len</I
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></TT
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> should contain the
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amount of data provided, which must match the size appropriate to the
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selected key.  The appropriate key values differ for each driver and
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are all listed in the file
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<TT
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CLASS="FILENAME"
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>&lt;cyg/io/config_keys.h&gt;</TT
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>.</P
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HREF="io-package-intro.html"
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>Prev</A
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ALIGN="center"
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><A
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HREF="ecos-ref.html"
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>Home</A
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>Introduction</TD
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HREF="io.html"
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>Up</A
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>Serial driver details</TD
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