Document revision date: 30 March 2001

The file SYS$EXAMPLES:CDROM_AUDIO.C contains an example of an application program that performs the following tasks:

• Defines standard symbolic names for the audio function codes representing SCSI audio commands.
• Defines representative AUCBs for each audio function code supported by the SCSI disk class driver.
• Issues a series of $QIO system service requests, each specifying the IO$_AUDIO function, that exercise the SCSI disk class driver to test its support for CD-ROM drives with audio capabilities.
• Converts LBA data returned by a GET_STATUS command in big-endian byte-ordering form to VAX little-ending byte-ordering form.

You can obtain information on all disk device characteristics by using the Get Device/Volume Information ($GETDVI) system service (refer to the OpenVMS System Services Reference Manual).

$GETDVI returns disk characteristics when you specify the item codes DVI$_DEVCHAR and DVI$_DEVCHAR2. Table 2-4 lists the possible characteristics for disk devices.

Table 2-4 Disk Device Characteristics

Characteristic1	Meaning
Dynamic Bits (Conditionally Set)
DEV$M_AVL	Device is on line and available.
DEV$M_CDP 2,3	Dual-path device with two unit control blocks (UCBs).
DEV$M_CLU 2	Device is available clusterwide.
DEV$M_2P 2	Device is dual-pathed.
DEV$M_FOR	Device is foreign.
DEV$M_MNT	Volume is mounted.
DEV$M_RCK	Perform data check on all reads.
DEV$M_WCK	Perform data check on all writes.
DEV$M_MSCP 2	Device is accessed using the mass storage control protocol.
DEV$M_RCT	Disk contains replacement and caching table.
DEV$M_SRV 2	For a cluster, device is served by the MSCP server.
Static Bits (Always Set)
DEV$M_FOD	Device is file-oriented.
DEV$M_IDV	Device is capable of input.
DEV$M_ODV	Device is capable of output.
DEV$M_RND	Device is capable of random access.
DEV$M_SHR	Device is shareable.

DVI$_DEVBUFSIZ returns the buffer size. The buffer size is the default to be used for disk transfers (this default is normally 512 bytes). DVI$_DEVTYPE and DVI$_DEVCLASS return the device type and class names, which are defined by the $DCDEF macro. The disk model determines the device type. For example, the device type for the RA81 is DT$_RA81. (Foreign device types take the form DT$_FD1 through DT$_FD8.) The device class for disks is DC$_DISK.

DVI$_CYLINDERS returns the number of cylinders per volume (that is, per disk), DVI$_TRACKS returns the number of tracks per cylinder, and DVI$_SECTORS returns the number of sectors per track. Values are returned as 4-byte decimal numbers.

DVI$_MAXBLOCK returns the maximum number of blocks (1 block = 512 bytes) that can be contained on the volume (that is, on the disk). Values are returned as 4-byte decimal numbers. This information can be used, for example, to determine the density of an RX02 diskette (single density = 494 blocks, double density = 988 blocks).

2.4 Disk Function Codes

Disk drivers can perform logical, virtual, and physical I/O functions. Foreign-mounted devices do not require privilege to perform logical and virtual I/O requests.

Logical and physical I/O functions allow access to volume storage and require only that the issuing process have access to the volume. However, DSA disks and the disk class driver (DUDRIVER) do not accept physical QIO data transfers or seek operations.

Virtual I/O functions require an ACP for Files-11 On-Disk Structure Level 1 files or an XQP for Files-11 On-Disk Structure Level 2 files. Virtual I/O functions must be executed in a prescribed order. First, you create and access a file, then you write information to that file, and lastly you deaccess the file. Subsequently, when you access the file, you read the information and then deaccess the file. Delete the file when the information is no longer useful.

Non-DSA disk devices can read or write up to 65,535 bytes in a single request. DSA devices connected to an HSC50 can transfer up to 4 billion bytes in a single request. In all cases, the maximum size of the transfer is limited by the number of pages that can be faulted into the process's working set, and then locked into physical memory. (The disk driver is responsible for any memory management functions of this type.) The size of the transfer does not affect the applicable quotas (direct I/O count, buffered I/O count, and asynchronous system trap (AST) count limit). These quotas refer to the number of outstanding I/O operations of each type, not the size of the I/O operation being performed.

The volume to which a logical or virtual function is directed must be mounted for the function actually to be executed. If it is not mounted, either a device not mounted or invalid volume status is returned in the I/O status block.

Table 2-5 lists the logical, virtual, and physical disk I/O functions and their function codes. Chapter 1 describes the QIO level interface to the disk device ACP.

Table 2-5 Disk I/O Functions

Function Code	Arguments	Type1	Function Modifiers	Function
IO$_ACCESS	P1, [P2],[P3],[P4],[P5]	V	IO$M_CREATE IO$M_ACCESS	Search a directory for a specified file and access the file if found.
IO$_ACPCONTROL	P1,[P2],[P3],[P4],[P5]	V	IO$M_DMOUNT	Perform miscellaneous control functions.
IO$_AVAILABLE		P		Clear volume valid; make DSA units available.
IO$_CREATE	P1,[P2],[P3],[P4],[P5]	V	IO$M_CREATE IO$M_ACCESS IO$M_DELETE	Create a directory entry or a file.
IO$_DEACCESS	P1,[P2],[P3],[P4],[P5]	V		Deaccess a file and, if specified, write final attributes in the file header.
IO$_DELETE	P1,[P2],[P3],[P4],[P5]	V	IO$M_DELETE	Remove a directory entry or file header, or both.
IO$_FORMAT	P1	P		Set density (RX02 only).
IO$_MODIFY	P1,[P2],[P3],[P4],[P5]	V		Modify the file attributes or allocation, or both.
IO$_PACKACK		P		Update UCB fields if RX02; initialize volume valid on other devices. Bring DSA units on line.
IO$_READLBLK 6	P1,P2,P3	L	IO$M_DATACHECK 2 IO$M_INHRETRY	Read logical block.
IO$_READPBLK 6	P1,P2,P3	P	IO$M_DATACHECK 2 IO$M_INHRETRY IO$M_INHSEEK 3	Read physical block. 5
IO$_READVBLK 6	P1,P2,P3	V	IO$M_DATACHECK 2 IO$M_INHRETRY	Read virtual block.
IO$_SEARCH	P1	P		Search for specified block or sector (only for TU58).
IO$_SEEK	P1	P		Seek to specified cylinder. 5
IO$_SENSECHAR		P		Sense the device-dependent characteristics and return them in the I/O status block.
IO$_SENSEMODE		L		Sense the device-dependent characteristics and return them in the I/O status block.
IO$_SETPRFPATH	P1	P	IO$M_FORCEPTH	Specifies a preferred path for DSA disks.
IO$_UNLOAD		P		Clear volume valid; make DSA units available and spin down the volume.
IO$_WRITECHECK 6	P1,P2,P3	P		Verify data written to disk by a previous write QIO. 2
IO$_WRITELBLK 6	P1,P2,P3	L	IO$M_DATACHECK 2 IO$M_ERASE IO$M_INHRETRY	Write logical block.
IO$_WRITEPBLK 6	P1,P2,P3	P	IO$M_DATACHECK 2 IO$M_ERASE IO$M_INHRETRY IO$M_INHSEEK 3 IO$M_DELDATA 4	Write physical block. 5
IO$_WRITEVBLK 6	P1,P2,P3	V	IO$M_DATACHECK 2 IO$M_ERASE IO$M_INHRETRY	Write virtual block.

The function-dependent arguments for IO$_CREATE, IO$_ACCESS, IO$_DEACCESS, IO$_MODIFY, and IO$_DELETE are as follows:

• P1---The address of the file information block (FIB) descriptor.
• P2---The address of the file name string descriptor (optional). If specified, the name is entered in the directory specified by the FIB.
• P3---The address of the word that is to receive the length of the resulting file name string (optional).
• P4---The address of a descriptor for a buffer that is to receive the resulting file name string (optional).
• P5---The address of a list of attribute descriptors (optional). If specified, the indicated attributes are read (IO$_ACCESS) or written (IO$_CREATE, IO$_DEACCESS, and IO$_MODIFY).

See Chapter 1 for more information on these functions.

The function-dependent arguments for IO$_READVBLK, IO$_READLBLK, IO$_WRITEVBLK, and IO$_WRITELBLK are as follows:

• P1---The starting virtual address of the buffer that is to receive the data from a read operation; or, in the case of a write operation, the virtual address of the buffer that is to be written on the disk. On OpenVMS Alpha, P1 can be a 64-bit address.
• P2---The number of bytes that are to be read from the disk, or written from memory to the disk. An even number must be specified if the controller is an RK611, RL11, RX211, or UDA50.
• P3---The starting virtual/logical disk address of the data to be transferred in a read operation; or, in a write operation, the disk address of the area that is to receive the data.
  In a virtual read or write operation, the address is expressed as a block number within the file, that is, block 1 of the file is virtual block 1. (Virtual block numbers are converted to logical block numbers using mapping windows that are set up by the file system ACP process.)
  In a logical read or write operation, the address is expressed as a block number relative to the start of the disk. For example, the first sector on the disk contains block 0 (or at least the beginning of block 0).

The function-dependent arguments for IO$_WRITEVBLK, IO$_WRITELBLK, and IO$_WRITEPBLK functions that include the IO$M_ERASE function modifier are as follows:

• P1---The starting virtual address of the buffer that contains a 4-byte, user-specified erase pattern. If the P1 address is 0, a longword of 0 will be used for the erase pattern. If the P1 address is nonzero, the contents of the 4 bytes starting at that address will be used as the erase pattern. Compaq recommends that the user specify a P1 address of 0 to lower system overhead. On OpenVMS Alpha, P1 can be a 64-bit address.

  Note DSA disk controllers provide controlled, assisted erasing for the IO$M_ERASE modifier (with virtual and logical write functions) only when the erase pattern is all zeros. If a nonzero erase pattern is used, there is a significant performance degradation with these disks. DSA disks do not accept physical QIO transfers.

• P2---The number of bytes of erase pattern to write to the disk. The number specified is rounded up to the next highest block boundary (512 bytes).
• P3---The starting virtual, logical, or physical disk address of the data to be erased.

The function-dependent arguments for IO$_WRITECHECK, IO$_READPBLK, and IO$_WRITEPBLK are as follows:

• P1---The starting virtual address of the buffer that is to receive the data in a read operation; or, in a write operation, the starting virtual address of the buffer that is to be written on the disk. Passed by reference. On OpenVMS Alpha, P1 can be a 64-bit address.
• P2---The number of bytes that are to be read from the disk, or written from memory to the disk. Passed by value. An even number must be specified if the controller is an RK611, RL11, or UDA50.
• P3---The starting physical disk address of the data to be read in a read operation; or, in a write operation, the starting physical address of the disk area that is to receive the data. Passed by value. The address is expressed as sector, track, and cylinder in the format shown in Figure 2-5. (On the RX01 and RX02, the high word specifies the track number rather than the cylinder number.) Check the UCB of a currently mounted device to determine the maximum physical address value for that type of device.

  Note On the RB80 and RM80, do not address cylinders 560 and 561. These two cylinders are used for diagnostic testing only.

The function-dependent argument for IO$_SEARCH is as follows:

P1---The physical disk address where the tape is positioned. The address is expressed as sector, track, and cylinder in the format shown in Figure 2-5.

Figure 2-5 Starting Physical Address

The function-dependent argument for IO$_SEEK is as follows:

P1---The physical cylinder number where the disk heads are positioned. The address is expressed in the format shown in Figure 2-6.

Figure 2-6 Physical Cylinder Number Format

The function-dependent argument for IO$_FORMAT is as follows:

P1---The density at which an RX02 diskette is reformatted (see Section 2.4.4).

The read function reads data into a specified buffer from disk starting at a specified disk address.

The operating system provides the following read function codes:

• IO$_READVBLK---Read virtual block
• IO$_READLBLK---Read logical block
• IO$_READPBLK---Read physical block

If a read virtual block function is directed to a volume that is mounted foreign, that function is converted to read logical block. If a read virtual block function is directed to a volume that is mounted structured, the volume is handled in the same way as for a file-structured device.

Three function-dependent arguments are used with these codes: P1, P2, and P3. These arguments are described in Section 2.4.

The data check function modifier (IO$M_DATACHECK) can be used with all read functions. If this modifier is specified, a data check operation is performed after the read operation completes. A data check operation is also performed if the volume that has been read, or the volume on which the file resides (virtual read) has the characteristic "data check all reads." Furthermore, a data check is performed after a virtual read if the file has the attribute "data check on read." The RX01 and RX02 drivers do not support the data check function.

If IO$M_DATACHECK is specified with a read function code to a TU58, or if the volume read has the characteristic "data check all reads," a read check operation is performed. This alters certain TU58 hardware parameters when the tape is read. (The read threshold in the data recovery circuit is increased; if the tape has any weak spots, errors are detected.)

The data check function modifier to a disk or tape can return five error codes in the I/O status block:

SS$_CTRLERR	SS$_DRVERR	SS$_MEDOFL
SS$_NONEXDRV	SS$_NORMAL

If no errors are detected, the disk or tape data is considered reliable.

The inhibit retry function modifier (IO$M_INHRETRY) can be used with all read functions. If this modifier is specified, all error recovery attempts are inhibited. IO$M_INHRETRY takes precedence over IO$M_DATACHECK. If both are specified and an error occurs, there is no attempt at error recovery and no data check operation is performed. If an error does not occur, the data check operation is performed.

2.4.2 Write

The write function writes data from a specified buffer to disk starting at a specified disk address.

The operating system provides the following write function codes:

• IO$_WRITEVBLK---Write virtual block
• IO$_WRITELBLK---Write logical block
• IO$_WRITEPBLK---Write physical block

If a write virtual block function is directed to a volume that is mounted foreign, the function is converted to write logical block. If a write virtual block function is directed to a volume that is mounted structured, the volume is handled in the same way as for a file-structured device.

Three function-dependent arguments are used with these codes: P1, P2, and P3. These arguments are described in Section 2.4.

The data check function modifier (IO$M_DATACHECK) can be used with all write operations. If this modifier is specified, a data check operation is performed after the write operation completes. A data check operation is also performed if the volume written, or the volume on which the file resides (virtual write), has the characteristic "data check all writes." Furthermore, a data check is performed after a virtual write if the file has the attribute "data check on write." The RX01 and RX02 drivers do not support the data check function.

If IO$M_DATACHECK is specified with a write function code to a TU58, or if the volume written has the characteristic "data check all writes," a write check operation is performed. The write check verifies data written on the tape. First, the specified data is written on the tape. Then the tape is reversed and the TU58 controller reads the data internally to perform a checksum verification. If the checksum verification is unsuccessful after eight attempts, the write check operation is aborted and an error status is returned.

The inhibit retry function modifier (IO$M_INHRETRY) can be used with all write functions. If that modifier is specified, all error recovery attempts are inhibited. IO$M_INHRETRY takes precedence over IO$M_DATACHECK. If both IO$M_INHRETRY and IO$M_DATACHECK are specified and an error occurs, there is no attempt at error recovery, and no data check operation is performed. If an error does not occur, the data check operation is performed. IO$M_INHRETRY has no effect on DSA disks.

The write deleted data function modifier (IO$M_DELDATA) can be used with the write physical block (IO$_WRITEPBLK) function to the RX02. If this modifier is specified, a deleted data address mark instead of the standard data address mark is written preceding the data. Otherwise, the operation of the IO$_WRITEPBLK function is the same; write data is transferred to the disk. When a successful read operation is performed on this data, the status code SS$_RDDELDATA is returned in the I/O status block rather than the usual SS$_NORMAL status code.

The IO$M_ERASE function modifier can be used with all write function codes to erase a user-selected part of a disk. This modifier propagates an erase pattern through the specified range. Section 2.4 describes the write function arguments to be used with IO$M_ERASE.

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