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Docs » Autodocs » cd.device » CD_CONFIG
CD_CONFIG -- Set drive preferences
IO REQUEST
io_Device preset by the call to OpenDevice()
io_Unit preset by the call to OpenDevice()
io_Command CD_CONFIG
io_Data pointer to first entry of TagList
io_Length 0
io_Error 0 for success, or an error code as defined in
<devices/cd.h>
This command sets one or more of the configuration items.
The configuration items are:
TAGCD_PLAYSPEED Default: 75
TAGCD_READSPEED Default: 75 (do not count on this)
TAGCD_READXLSPEED Default: 75
TAGCD_SECTORSIZE Default: 2048
TAGCD_XLECC Default: 1 (on)
TAGCD_EJECTRESET Default: can be 0 (off) or 1 (on)
The speed settings are described in the number of frames (sectors)
per second. All CD-ROM drives are capable of the 75 frames/second
rate. Some drives are capable of 150 frames/second, and some even
more. To determine the maximum frame rate of the drive, use the
CD_INFO command. Valid values for caddyless Commodore CD-ROM drives
are 75 and 150 (normal speed and double speed). All other values are
invalid. You should always make sure the drive is capable of the
configuration you are requesting by either using the CD_INFO command,
and/or by checking for an error condition after submitting your
request.
There are three different types of CD-ROM sectors. Mode 1 sectors
(2048 bytes), mode 2 form 1 sectors (2048 bytes), and mode 2 form 2
sectors (2328 bytes). Normally, disks are encoded in Mode 1 format.
Mode 2 form 1 is basically the same as mode 1; however, the mode 2
form 2 sector format contains no CD-ROM error correction information.
In order to read information encoded in this sector format, the
drive's sector size must be configured to 2328 byte sectors.
Error correction (ECC) of the READXL command can be turned off or
on with this command. Error correction can be implemented in either
hardware or software (depending on the CD-ROM drive). When ECC is
implemented in software, CPU usage can become bursty. Errors rarely
occur on CDs unless they have numerous scratches, but when they do
occur, they will cause a loss of CPU bandwith. When ECC is
implemented in hardware, no CPU bandwidth is lost -- in this case,
ECC will always be on no matter how you configure the drive because
it is free. The READXL command is used primarily for displaying
movie-like data. In this case, speed is essential and data integrety
is not; however, if the CPU is not being utilized during an XL
animation there is no need to disable ECC (since the bandwidth is
there to be used). The only time ECC should be disabled is when you
are doing intense calculations in the background of a READXL command,
AND your program is time-critical. Do not forget to change this back
when you are done!
To make the computer reset when a CD is ejected (for an application
that does not exit), use the TAGCD_EJECTRESET tag. When possible,
titles should be able to exit cleanly back to Workbench. Error
conditions should be monitored when doing disk I/O.
/* Configure ReadXL for double-speed reading and turn off ECC when */
/* the ReadXL command is used. */
struct TagItem ConfigList[] = {
{ TAGCD_READXLSPEED, 150 },
{ TAGCD_XLECC, 0 },
{ TAG_END, 0 }
};
ior->io_Command = CD_CONFIG;
ior->io_Data = (APTR)&ConfigList;
ior->io_Length = 0;
DoIO(ior);
if (ior->io_Error) printf("Could not be configured\n");
Setting the configuration will not modify the behavior of a read or
play command already in progress.
This can be a very dangerous command. If for instance you set
TAGCD_SECTORSIZE to 2328, you will no longer be able to read any
data encoded at 2048 byte sectors (e.g. the file system will not be
able to read the disk anymore). After you read any data stored with
this sector format, you should immediately configure back to the
original default value (even if the read failed -- the disk could
be removed in the middle of your read). You should NEVER use this
command if you are not the exclusive owner of your disk.
TAG_IGNORE, TAG_MORE, and TAG_SKIP do not work. Do not use these.
When switching speeds from single to double (or double to single),
If the drive is prefetching in single-speed the data you are going
to use in double-speed, the drive will not switch to double-speed
(and visa versa). To avoid this problem, switch to the desired speed,
begin reading at least 4k into the data (just read two bytes), then
begin reading at the beginning. This will force the prefetch buffer
to clear and issue a new read command with the desired speed.
(Fixed in 40.24).
CD_INFO(), <utility/tagitem.h>
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