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><H1
><A
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>Chapter 31. User API</H1
><P
>The CAN driver uses the standard eCos I/O API functions. All functions 
except <CODE
CLASS="FUNCTION"
>cyg_io_lookup()</CODE
> require an I/O "handle".</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 values 
will be <CODE
CLASS="VARNAME"
>ENOERR</CODE
>, <CODE
CLASS="VARNAME"
>-EINTR</CODE
> and 
<CODE
CLASS="VARNAME"
>-EAGAIN</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 
<CODE
CLASS="PARAMETER"
>len</CODE
> 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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><PRE
CLASS="PROGRAMLISTING"
>// Lookup a CAN 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 CAN 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
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><TD
><PRE
CLASS="PROGRAMLISTING"
>// Send a CAN message
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 one single CAN message (not a buffer of CAN messages) 
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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><TD
><PRE
CLASS="PROGRAMLISTING"
>// Read one CAN event from 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 one single CAN event 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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><TD
><PRE
CLASS="PROGRAMLISTING"
>// Read configuration of a CAN 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 
are all listed in the file <TT
CLASS="FILENAME"
>&lt;cyg/io/config_keys.h&gt;</TT
>.</P
><TABLE
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><TD
><PRE
CLASS="PROGRAMLISTING"
>// Change configuration of a CAN 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 are all listed in the file
<TT
CLASS="FILENAME"
>&lt;cyg/io/config_keys.h&gt;</TT
>.</P
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