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<article>
<title>Diskette Sector I/O Routines
<author>Christian Groessler, <htmlurl url="mailto:chris@groessler.org" name="chris@groessler.org">
<date>20-Feb-2005

<abstract>
The cc65 library provides functions to read and write raw disk sectors.
Include the dio.h header file to get the necessary definitions.
</abstract>

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<sect>Opening the disk for low level I/O<p>

Prior to using these functions a handle to the drive has to be obtained. This
is done with the <tt>dio_open</tt> function. After use, the handle should be
released with the <tt>dio_close</tt> function.

<tscreen><verb>
    dhandle_t __fastcall__ dio_open (driveid_t drive_id);
</verb></tscreen>

The <tt>drive_id</tt> specifies the drive to access, with 0 being the first
disk drive, 1 the second, and so on.

<tscreen><verb>
    unsigned char __fastcall__ dio_close (dhandle_t handle);
</verb></tscreen>

Closes a handle obtained by <tt>dio_open</tt>. Returns status code.
<p>

<sect>Reading and writing sectors<p>

The read and write functions are:

<tscreen><verb>
    unsigned char __fastcall__ dio_read (dhandle_t handle,
    					 sectnum_t sect_num,
                                         void *buffer);
</verb></tscreen>

This function will read the sector specified by <tt>sect_num</tt> into the memory
location at buffer.

<tscreen><verb>
    unsigned char __fastcall__ dio_write (dhandle_t handle,
    					  sectnum_t sect_num,
                                          const void *buffer);
</verb></tscreen>

This function will write the memory contents at buffer to the sector specified
by <tt>sect_num</tt>. No verify is performed.

<tscreen><verb>
    unsigned char __fastcall__ dio_write_verify (dhandle_t handle,
    						 sectnum_t sect_num,
                                             	 const void *buffer);
</verb></tscreen>

This function will write the memory contents at buffer to the sector specified
by <tt>sect_num</tt>. A verification is performed.
<p>

Use the <tt><ref name="dio_query_sectsize" id="sectsizecount"></tt> function to query
the size of a sector and the <tt><ref name="dio_query_sectcount" id="sectsizecount"></tt>
function to query the number of available sectors.
<p>

All these functions will return 0 for success and an OS specific error code in
case of failure.
<p>

<sect>Querying sector size and count<label id="sectsizecount"><p>

Some systems support multiple diskette formats which have different sector sizes
and/or different sector counts.
<p>

The following function returns the sector size of the currently inserted disk:

<tscreen><verb>
    sectsize_t __fastcall__ dio_query_sectsize(dhandle_t handle);
</verb></tscreen>

On the Atari platform, the sector size is handled specially. Please refer
to the DIO section in the <htmlurl url="atari.html" name="Atari">
specific platform documentation.
<p>

The following function returns the sector count of the currently inserted disk:

<tscreen><verb>
    sectnum_t __fastcall__ dio_query_sectcount(dhandle_t handle);
</verb></tscreen>

<sect>Converting sector numbers<p>

Since the read and write functions expect a sector number, for systems where
the sectors aren't addressed by a logical sector number (e.g. CBM drives),
there are 2 conversion functions. One of them converts a logical sector number
to a head/track/sector triple. The other conversion function works the other
way round.

<tscreen><verb>
    unsigned char __fastcall__ dio_phys_to_log (dhandle_t handle,
                                                const dio_phys_pos *physpos,
                                                sectnum_t *sectnum);
</verb></tscreen>

This function converts track/head/sector to logical sector number.

<tscreen><verb>
    unsigned char __fastcall__ dio_log_to_phys (dhandle_t handle,
                                                const _sectnum_t *sectnum,
                                                dio_phys_pos *physpos);
</verb></tscreen>

This function converts a logical sector number to track/head/sector notation.
<p>

Note, that on systems which natively use logical sector numbers (e.g. Atari),
the conversion functions are dummies. They ignore head/track
(<tt>dio_phys_to_log</tt>) or return them as zero (<tt>dio_log_to_phys</tt>).
The logical sector number is returned as physical sector and vice versa.
<p>


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