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>User API</TITLE
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><H1
><A
NAME="IO-USER-API"
></A
>Chapter 10. User API</H1
><P
>All functions, except <CODE
CLASS="FUNCTION"
>cyg_io_lookup()</CODE
>
require an I/O &#8220;handle&#8221;.</P
><P
>All functions return a value of the type <SPAN
CLASS="TYPE"
>Cyg_ErrNo</SPAN
>. If an
error condition is detected, this value will be negative and the
absolute value indicates the actual error, as specified in
<TT
CLASS="FILENAME"
>cyg/error/codes.h</TT
>. The only other legal return
value will be <CODE
CLASS="VARNAME"
>ENOERR</CODE
>. All other function arguments
are pointers (references). This allows the drivers to pass information
efficiently, both into and out of the driver. The most striking
example of this is the &#8220;length&#8221; value passed to the read
and write functions. This parameter contains the desired length of
data on input to the function and the actual transferred length on
return.</P
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><TD
><PRE
CLASS="PROGRAMLISTING"
>// Lookup a device and return its handle 
  Cyg_ErrNo <CODE
CLASS="FUNCTION"
>cyg_io_lookup</CODE
>( 
    const char <CODE
CLASS="PARAMETER"
>*name</CODE
>,
    cyg_io_handle_t <CODE
CLASS="PARAMETER"
>*handle</CODE
> )</PRE
></TD
></TR
></TABLE
><P
>This function maps a device name onto an appropriate handle. If the
named device is not in the system, then the error
<CODE
CLASS="VARNAME"
>-ENOENT</CODE
> is returned. If the device is found, then
the handle for the device is returned by way of the handle pointer
<CODE
CLASS="PARAMETER"
>*handle</CODE
>.</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>// Write data to a device 
Cyg_ErrNo <CODE
CLASS="FUNCTION"
>cyg_io_write</CODE
>( 
    cyg_io_handle_t <CODE
CLASS="PARAMETER"
>handle</CODE
>,
    const void <CODE
CLASS="PARAMETER"
>*buf</CODE
>,
    cyg_uint32 <CODE
CLASS="PARAMETER"
>*len</CODE
> )</PRE
></TD
></TR
></TABLE
><P
>This function sends data to a device. The size of data to send is
contained in <CODE
CLASS="PARAMETER"
>*len</CODE
> and the actual size sent will
be returned in the same place.</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>// Read data from a device 
Cyg_ErrNo <CODE
CLASS="FUNCTION"
>cyg_io_read</CODE
>( 
    cyg_io_handle_t <CODE
CLASS="PARAMETER"
>handle</CODE
>,
    void <CODE
CLASS="PARAMETER"
>*buf</CODE
>,
    cyg_uint32 <CODE
CLASS="PARAMETER"
>*len</CODE
> )</PRE
></TD
></TR
></TABLE
><P
>This function receives data from a device. The desired size of data to
receive is contained in <CODE
CLASS="PARAMETER"
>*len</CODE
> and the actual
size obtained will be returned in the same place.</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>// Get the configuration of a device 
Cyg_ErrNo <CODE
CLASS="FUNCTION"
>cyg_io_get_config</CODE
>( 
    cyg_io_handle_t <CODE
CLASS="PARAMETER"
>handle</CODE
>,
    cyg_uint32 <CODE
CLASS="PARAMETER"
>key</CODE
>,
    void *<CODE
CLASS="PARAMETER"
>buf</CODE
>,
    cyg_uint32 *<CODE
CLASS="PARAMETER"
>len</CODE
> )</PRE
></TD
></TR
></TABLE
><P
>This function is used to obtain run-time configuration about a
device. The type of information retrieved is specified by the
<CODE
CLASS="PARAMETER"
>key</CODE
>. The data will be returned in the given
buffer. The value of <CODE
CLASS="PARAMETER"
>*len</CODE
> should contain the
amount of data requested, which must be at least as large as the size
appropriate to the selected key. The actual size of data retrieved is
placed in <CODE
CLASS="PARAMETER"
> *len</CODE
>. The appropriate key values
differ for each driver and are all listed in the file
<TT
CLASS="FILENAME"
>&lt;cyg/io/config_keys.h&gt;</TT
>.</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>// Change the configuration of a device 
Cyg_ErrNo <CODE
CLASS="FUNCTION"
>cyg_io_set_config</CODE
>( 
    cyg_io_handle_t <CODE
CLASS="PARAMETER"
>handle</CODE
>,
    cyg_uint32 <CODE
CLASS="PARAMETER"
>key</CODE
>,
    const void <CODE
CLASS="PARAMETER"
>*buf</CODE
>,
    cyg_uint32 <CODE
CLASS="PARAMETER"
>*len</CODE
> )</PRE
></TD
></TR
></TABLE
><P
>This function is used to manipulate or change the run-time
configuration of a device. The type of information is specified by the
<CODE
CLASS="PARAMETER"
>key</CODE
>. The data will be obtained from the given
buffer. The value of <CODE
CLASS="PARAMETER"
>*len</CODE
> should contain the
amount of data provided, which must match the size appropriate to the
selected key.  The appropriate key values differ for each driver and
are all listed in the file
<TT
CLASS="FILENAME"
>&lt;cyg/io/config_keys.h&gt;</TT
>.</P
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