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NAME    [Toc]    [Back]

     cd -- SCSI CD-ROM driver

SYNOPSIS    [Toc]    [Back]

     device cd
     options "CHANGER_MAX_BUSY_SECONDS=11"

DESCRIPTION    [Toc]    [Back]

     The cd driver provides support for a SCSI CD-ROM (Compact Disc-Read Only
     Memory) drive.  In an attempt to look like a regular disk, the cd driver
     synthesizes a partition table, with one partition covering the entire
     CD-ROM.  It is possible to modify this partition table using
     disklabel(8), but it will only last until the CD-ROM is unmounted.  In
     general the interfaces are similar to those described by ad(4) and da(4).

     As the SCSI adapter is probed during boot, the SCSI bus is scanned for
     devices.  Any devices found which answer as CDROM (type 5) or WORM (type
     4) type devices will be `attached' to the cd driver.  Prior to
     FreeBSD 2.1, the first device found will be attached as cd0 the next,
     cd1, etc.	Beginning in FreeBSD 2.1 it is possible to specify what cd
     unit a device should come on line as; refer to scsi(4) for details on
     kernel configuration.

     The system utility disklabel(8) may be used to read the synthesized disk
     label structure, which will contain correct figures for the size of the
     CD-ROM should that information be required.


     Any number of CD-ROM devices may be attached to the system regardless of
     system configuration as all resources are dynamically allocated.

IOCTLS    [Toc]    [Back]

     The following ioctl(2) calls which apply to SCSI CD-ROM drives are
     defined in the header files <sys/cdio.h> and <sys/disklabel.h>.


     DIOCSDINFO 	  (struct disklabel) Read or write the in-core copy of
			  the disklabel for the drive.	The disklabel is initialized
 with information read from the scsi inquiry
			  commands, and should be the same as the information
			  printed at boot.  This structure is defined in

     CDIOCCAPABILITY	  (struct ioc_capability) Retrieve information from
			  the drive on what features it supports.  The information
 is returned in the following structure:

				struct ioc_capability {
					u_long	play_function;
				#define CDDOPLAYTRK	0x00000001
					/* Can play tracks/index */
				#define CDDOPLAYMSF	0x00000002
					/* Can play msf to msf */
				#define CDDOPLAYBLOCKS	0x00000004
					/* Can play range of blocks */
				#define CDDOPAUSE	0x00000100
					/* Output can be paused */
				#define CDDORESUME	0x00000200
					/* Output can be resumed */
				#define CDDORESET	0x00000400
					/* Drive can be completely reset */
				#define CDDOSTART	0x00000800
					/* Audio can be started */
				#define CDDOSTOP	0x00001000
					/* Audio can be stopped */
				#define CDDOPITCH	0x00002000
					/* Audio pitch can be changed */

					u_long	routing_function;
				#define CDREADVOLUME	0x00000001
					/* Volume settings can be read */
				#define CDSETVOLUME	0x00000002
					/* Volume settings can be set */
				#define CDSETMONO	0x00000100
					/* Output can be set to mono */
				#define CDSETSTEREO	0x00000200
					/* Output can be set to stereo (def) */
				#define CDSETLEFT	0x00000400
					/* Output can be set to left only */
				#define CDSETRIGHT	0x00000800
					/* Output can be set to right only */
				#define CDSETMUTE	0x00001000
					/* Output can be muted */
				#define CDSETPATCH	0x00008000
					/* Direct routing control allowed */

					u_long	special_function;
				#define CDDOEJECT	0x00000001
					/* The tray can be opened */
				#define CDDOCLOSE	0x00000002
					/* The tray can be closed */
				#define CDDOLOCK	0x00000004
					/* The tray can be locked */
				#define CDREADHEADER	0x00000100
					/* Can read Table of Contents */
				#define CDREADENTRIES	0x00000200
					/* Can read TOC Entries */
				#define CDREADSUBQ	0x00000200
					/* Can read Subchannel info */
				#define CDREADRW	0x00000400
					/* Can read subcodes R-W */
				#define CDHASDEBUG	0x00004000
					/* The tray has dynamic debugging */

     CDIOCPLAYTRACKS	  (struct ioc_play_track) Start audio playback given a
			  track address and length.  The structure is defined
			  as follows:

				struct ioc_play_track
					u_char	start_track;
					u_char	start_index;
					u_char	end_track;
					u_char	end_index;

     CDIOCPLAYBLOCKS	  (struct ioc_play_blocks) Start audio playback given
			  a block address and length.  The structure is
			  defined as follows:

				struct ioc_play_blocks
					int	blk;
					int	len;

     CDIOCPLAYMSF	  (struct ioc_play_msf) Start audio playback given a
			  `minutes-seconds-frames' address and length.	The
			  structure is defined as follows:

				struct ioc_play_msf
					u_char	start_m;
					u_char	start_s;
					u_char	start_f;
					u_char	end_m;
					u_char	end_s;
					u_char	end_f;

     CDIOCREADSUBCHANNEL  (struct ioc_read_subchannel) Read information from
			  the subchannel at the location specified by this

				struct ioc_read_subchannel {
					u_char address_format;
				#define CD_LBA_FORMAT	1
				#define CD_MSF_FORMAT	2
					u_char data_format;
				#define CD_SUBQ_DATA		0
				#define CD_MEDIA_CATALOG	2
				#define CD_TRACK_INFO		3
					u_char track;
					int	data_len;
					struct	cd_sub_channel_info *data;

     CDIOREADTOCHEADER	  (struct ioc_toc_header) Return summary information
			  about the table of contents for the mounted CD-ROM.
			  The information is returned into the following

				struct ioc_toc_header {
					u_short len;
					u_char	starting_track;
					u_char	ending_track;

     CDIOREADTOCENTRYS	  (struct ioc_read_toc_entry) Return information from
			  the table of contents entries mentioned.  (Yes, this
			  command name is misspelled.) The argument structure
			  is defined as follows:

				struct ioc_read_toc_entry {
					u_char	address_format;
					u_char	starting_track;
					u_short data_len;
					struct	cd_toc_entry *data;
			  The requested data is written into an area of size
			  data_len and pointed to by data.

     CDIOCSETPATCH	  (struct ioc_patch) Attach various audio channels to
			  various output channels.  The argument structure is
			  defined thusly:

				struct ioc_patch {
					u_char	patch[4];
					/* one for each channel */


     CDIOCSETVOL	  (struct ioc_vol) Get (set) information about the
			  volume settings of the output channels.  The argument
 structure is as follows:

				struct	ioc_vol
					u_char	vol[4];
					/* one for each channel */

     CDIOCSETMONO	  Patch all output channels to all source channels.

     CDIOCSETSTEREO	  Patch left source channel to the left output channel
			  and the right source channel to the right output

     CDIOCSETMUTE	  Mute output without changing the volume settings.


     CDIOCSETRIGHT	  Attach both output channels to the left (right)
			  source channel.


     CDIOCCLRDEBUG	  Turn on (off) debugging for the appropriate device.


     CDIOCRESUME	  Pause (resume) audio play, without resetting the
			  location of the read-head.

     CDIOCRESET 	  Reset the drive.


     CDIOCSTOP		  Tell the drive to spin-up (-down) the CD-ROM.


     CDIOCPREVENT	  Tell the drive to allow (prevent) manual ejection of
			  the CD-ROM disc.  Not all drives support this feature.

     CDIOCEJECT 	  Eject the CD-ROM.

     CDIOCCLOSE 	  Tell the drive to close its door and load the media.
			  Not all drives support this feature.

     CDIOCPITCH 	  (struct ioc_pitch) For drives that support it, this
			  command instructs the drive to play the audio at a
			  faster or slower rate than normal.  Values of speed
			  between -32767 and -1 result in slower playback; a
			  zero value indicates normal speed; and values from 1
			  to 32767 give faster playback.  Drives with less
			  than 16 bits of resolution will silently ignore
			  less-significant bits.  The structure is defined

				struct	ioc_pitch
					short	speed;

NOTES    [Toc]    [Back]

     When a CD-ROM is changed in a drive controlled by the cd driver, then the
     act of changing the media will invalidate the disklabel and information
     held within the kernel.  To stop corruption, all accesses to the device
     will be discarded until there are no more open file descriptors referencing
 the device.  During this period, all new open attempts will be
     rejected.	When no more open file descriptors reference the device, the
     first next open will load a new set of parameters (including disklabel)
     for the drive.

     The audio code in the cd driver only support SCSI-2 standard audio commands.
  As many CD-ROM manufacturers have not followed the standard,
     there are many CD-ROM drives for which audio will not work.  Some work is
     planned to support some of the more common `broken' CD-ROM drives; however,
 this is not yet under way.

     The cd driver attempts to automatically determine whether the drive it is
     talking to supports 6 byte or 10 byte MODE SENSE/MODE SELECT operations.
     Many SCSI drives only support 6 byte commands, and ATAPI drives only support
 10 byte commands.  The cd driver first attempts to determine whether
     the protocol in use typically supports 6 byte commands by issuing a CAM
     Path Inquiry CCB.	It will then default to 6 byte or 10 byte commands as
     appropriate.  After that, the cd driver defaults to using 6 byte commands
     (assuming the protocol the drive speaks claims to support 6 byte commands),
 until one fails with a SCSI ILLEGAL REQUEST error.  Then it tries
     the 10 byte version of the command to see if that works instead.  Users
     can change the default via per-drive sysctl variables and loader tunables.
  The variable names are the same in both instances:


     Where ``%d'' is the unit number of the drive in question.	Valid minimum
     command sizes are 6 and 10.  Any value above 6 will be rounded to 10, and
     any value below 6 will be rounded to 6.

CHANGER OPERATION    [Toc]    [Back]

     This driver has built-in support for LUN-based CD changers.  A LUN-based
     CD changer is a drive that can hold two or more CDs, but only has one CD
     player mechanism.	Each CD in the drive shows up as a separate logical
     unit on the SCSI bus.  The cd driver automatically recognizes LUN-based
     changers, and routes commands for changers through an internal scheduler.
     The scheduler prevents changer "thrashing", which is caused by sending
     commands to different LUNs in the changer at the same time.

     The scheduler honors minimum and maximum time quanta that the driver will
     spend on a particular LUN.  The minimum time is the guaranteed minimum
     amount of time that the driver will spend on a given LUN, even if there
     is no outstanding I/O for that LUN.  The maximum time is the maximum
     amount of time the changer will spend on a LUN if there is outstanding
     I/O for another LUN.  If there is no outstanding I/O for another LUN, the
     driver will allow indefinite access to a given LUN.

     The minimum and maximum time quanta are configurable via kernel options
     and also via sysctl and kernel tunable variables.	The kernel options

     options "CHANGER_MAX_BUSY_SECONDS=11"

     The sysctl/kernel tunable variables are:


     It is suggested that the user try experimenting with the minimum and maximum
 timeouts via the sysctl variables to arrive at the proper values for
     your changer.  Once you have settled on the proper timeouts for your
     changer, you can then put them in your kernel config file.

     If your system does have a LUN-based changer, you may notice that the
     probe messages for the various LUNs of the changer will continue to
     appear while the boot process is going on.  This is normal, and is caused
     by the changer scheduling code.

FILES    [Toc]    [Back]

     /dev/cd[0-9][a-h]	raw mode CD-ROM devices

DIAGNOSTICS    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

     da(4), scsi(4), disklabel(5), disklabel(8), cd(9)

BUGS    [Toc]    [Back]

     The names of the structures used for the third argument to ioctl() were
     poorly chosen, and a number of spelling errors have survived in the names
     of the ioctl() commands.

     There is no mechanism currently to set different minimum and maximum
     timeouts for different CD changers; the timeout values set by the kernel
     options or the sysctl variables apply to all LUN-based CD changers in the
     system.  It is possible to implement such support, but the sysctl implementation
 at least would be rather inelegant, because of the current
     inability of the sysctl code to handle the addition of nodes after compile
 time.  Thus, it would take one dynamically sized sysctl variable and
     a userland utility to get/set the timeout values.	Implementation of separate
 timeouts for different CD devices in the kernel config file would
     likely require modification of config(8) to support the two timeouts when
     hardwiring cd devices.

HISTORY    [Toc]    [Back]

     This cd driver is based upon the cd driver written by Julian Elischer,
     which appeared in 386BSD 0.1.  The CAM version of the cd driver was written
 by Kenneth Merry and first appeared in FreeBSD 3.0.

FreeBSD 5.2.1		       September 2, 2003		 FreeBSD 5.2.1
[ Back ]
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