NAME
        TD_FORMAT/ETD_FORMAT -- format a track on a disk.

   FUNCTION
        These commands are used to write data to a track that either
        has not yet been formatted or has had a hard error on a standard write
        command. TD_FORMAT completely ignores all data currently on a track and
        does not check for disk change before performing the command. The
        io_Data field must point to at least one track worth of data. The
        io_Offset field must be track aligned, and the io_Length field must be
        in units of track length (that is, NUMSEC*TD_SECTOR).

        The device will format the requested tracks, filling each sector with
        the contents of the buffer pointed to by io_Data. You
        should do a read pass to verify the data.

        If you have a hard write error during a normal write, you may find it
        possible to use the TD_FORMAT command to reformat the track as part of
        your error recovery process. ETD_FORMAT will write the sector label
        area if iotd_SecLabel is non-NULL.

   IO REQUEST INPUT
        io_Device       preset by the call to opendevice()
        io_Unit         preset by the call to opendevice()
        io_Command      TD_FORMAT or ETD_FORMAT
        io_Flags        0 or IOF_QUICK
        io_Data         points to a buffer containing the data to write to the
                        track, must be at least as large as io_Length.
        io_Length       number of bytes to format, must be a multiple of
                        (TD_SECTORS * NUMSEC).
        io_Offset       byte offset from the start of the disk for the track to
                        format, must be a multiple of (TD_SECTORS * NUMSEC).
        iotd_Count      (ETD_FORMAT only) maximum allowable change counter
                        value.
        iotd_SecLabel   (ETD_FORMAT only) NULL or sector label buffer pointer.
                        If provided, the buffer must be a multiple of
                        (TD_LABELSIZE * NUMSEC).

   IO REQUEST RESULT
        io_Error - 0 for success, or an error code as defined in
                   <devices/trackdisk.h>

   NOTES
        Under versions of Kickstart earlier than V36, the io_Data had to
        point to a buffer in chip memory. This restriction is no longer
        present as of Kickstart V36 and beyond.

   SEE ALSO
        cmd_write, td_rawwrite