XP(4)

NAME
xp - generic SMD moving-head disk

SYNOPSIS
/sys/conf/SYSTEM:
	NXPC	xp_controllers	# Number of controllers
	NXPD	xp_drives		# RM02/03/05, RP04/05/06,
					# CDC 9766, Fuji 160, etc.
	BADSECT	NO		# Bad sector handling (see BUGS)
/etc/dtab:
	#Name	Unit#	Addr	Vector	Br	Handler(s)		# Comments
	xp	?	176700	254	5	xpintr		# xp driver
major device number(s):
	raw: 19
	block: 10
minor device encoding:
	bits 0007 specify partition of XP drive
	bits 0370 specify XP drive

DESCRIPTION
The xp driver is a generic SMD storage module disk driver. It can be adapted to most SMD controllers although bootstrapping will not necessarily be directly possible. The drives are numbered from 0 to n on controller 0, from n+1 to m on controller 1, etc. The drives may have different geometries.

The xp driver is unique amoungst 2BSD drivers in its numbering of drives. Other drivers (ra for example) number drives 0 thru 7 on controller 1, 8 thru 15 on controller 2 and so on. xp on the other hand can have drives 0 and 1 on controller 1, drives 2, 3, 4 and 5 on controller 2 and drives 6, 7 and 8 on controller 3. This is different from boot's view of the world, so if you are booting from other than unit 0 you may have to experiment a bit.

Files with minor device numbers 0 through 7 refer to various portions of drive 0; minor devices 8 through 15 refer to drive 1, etc. The standard device names begin with ``xp'' followed by the drive number and then a letter a-h for partitions 0-7 respectively. The character ? stands here for a drive number in the range 0-7.

The block files access the disk via the system's normal buffering mechanism and may be read and written without regard to physical disk records. There is also a `raw' interface which provides for direct transmission between the disk and the user's read or write buffer. A single read or write call results in exactly one I/O operation and therefore raw I/O is considerably more efficient when many words are transmitted. The names of the raw files conventionally begin with an extra `r.'

In raw I/O the buffer must begin on a word (even) boundary, and counts should be a multiple of 512 bytes (a disk sector). Likewise lseek calls should specify a multiple of 512 bytes.

DISK SUPPORT
Disks must be labeled using either the standalone disklabel program on the boot tape or with the disklabel(8) program. The kernel no longer attempts to determine the drive type and geometry, instead reading this information from the disklabel. There are no partition tables coded into the xp driver, these must be placed on the drive with disklabel.

Special files should only be created for the partitions that are actually used, as the overlap in these addresses could lead to confusion otherwise. Traditionally the xp?a partition is normally used for the root file system, the xp?b partition as a swap area, and the xp?c partition for pack-pack copying (it maps the entire disk).

FILES
/dev/xp[0-7][a-h]    block files
/dev/rxp[0-7][a-h]    raw files
/dev/MAKEDEV    script to create special files
/dev/MAKEDEV.local    script to localize special files

SEE ALSO
hk(4), ra(4), ram(4), rk(4), rl(4), rp(4), rx(4), si(4), dtab(5), autoconfig(8), newfs(8)

DIAGNOSTICS
xp%d%c: hard error sn%d cs2=%b er1=%b. An unrecoverable error occurred during transfer of the specified sector of the specified disk partition. The contents of the two error registers are also printed in octal and symbolically with bits decoded. The error was either unrecoverable, or a large number of retry attempts (including offset positioning and drive recalibration) could not recover the error.

xp%d: write locked. The write protect switch was set on the drive when a write was attempted. The write operation is not recoverable.

xp%d%c: soft ecc sn%d. A recoverable ECC error occurred on the specified sector of the specified disk partition. This happens normally a few times a week. If it happens more frequently than this the sectors where the errors are occurring should be checked to see if certain cylinders on the pack, spots on the carriage of the drive or heads are indicated.

xp%d: unknown device type 0%o. The number in the drive's drive type register is unknown to the xp driver.

BUGS
In raw I/O read and write(2) truncate file offsets to 512-byte block boundaries, and write scribbles on the tail of incomplete blocks. Thus, in programs that are likely to access raw devices, read, write and lseek(2) should always deal in 512-byte multiples.

DEC-standard error logging should be supported.

The kernel uses partition 'h' to access the badblock information. This should have been 'c' except that almost all of the /etc/disktab entries (and thus existing systems) use 'h' for this purpose. Unless you are very careful with disklabel|(8) (to make certain that no data partition overlaps the badblock area) you should probably leave BADSECT undefined in the kernel config file.