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Test Your Knowledge in Computers #507
Difficulty: Easy
In the following code: x = 3y + 7; the variables x and y represent numbers that can take on a number of different values.
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autoconfig(8) [bsd man page]

AUTOCONFIG(8)						      System Manager's Manual						     AUTOCONFIG(8)

NAME
autoconfig - configure the running system to the hardware SYNOPSIS
autoconfig [-i ifile] [-n nfile] [-k kfile] [-v] [-d] [-c] DESCRIPTION
Autoconfig is called by init(8) to configure the currently running system. Init checks the exit status of autoconfig to determine if the configuration was successful. Autoconfig reads the device table /etc/dtab for a list of devices which may be on the system. It first ver- ifies that the kernel has an attach routine for each device (and therefore has a device handler) and that the kernel has a probe routine. It then checks each of these devices to see if it is present, and if it is, attempts to make it interrupt (if possible) to verify that the interrupt vector is correct. The interrupt vector is checked to see that it has not previously been used. An interrupt through any of the device's consecutive vectors is sufficient. Devices which use programmable vectors (MSCP and TMSCP) are permitted to have a value of 0 in the dtab vector field. This special value tells autoconfig to call the kernel's get next available vector routine and assign that to the device. For programmable vector devices if the dtab vector field is non 0 then the value specified in the dtab file is used. In both cases the driver is called at its xxVec() rou- tine with the vector being assigned to the device. If the address and vector are correct, it then attaches the device by passing the address and unit number to the kernel's attach routine and setting up the interrupt vector according to the interrupt handlers and priority listed in the device table. If the unit number is given as a '?' in the device table, it will be assigned the next available unit number if the device exists. If the device is not present or the vector is incorrect, and if the unit number was specified (not a '?'), then the kernel is notified that that unit is not present, preventing accesses to a nonexistent device address. There are only a few flags which are mostly useful for debugging but for completeness, here they are. -i ifile Use ifile instead of /etc/dtab as the device table. -n nfile Use nfile instead of /unix for finding the namelist of the currently running kernel. -k kfile The file kfile should be used instead of /dev/kmem to alter and read kernel memory. -v Verbose output, indicates reason for rejecting any device in the device table. Normally only attached devices are reported. -c Report error messages for devices skipped because of problems with their interrupt vectors. -d Turn on debugging mode. Shows many gory details of autoconfig's internal processing. BUGS
Devices of the same type must be listed with ascending unit numbers or with wildcards. Disks that could be root devices must have their addresses and vectors initialized in the kernel; the kernel uses a root attach entry in the block device switch to allow disk drivers to do any probes necessary before autoconfiguration. Must be run only by init(8). There is a flag set in the kernel that autoconfig has already run, running autoconfig a second time results in the error: "namelist doesn't match running kernel." Autoconfig attempts to open /dev/kmem for write. If the kernel is in securelevel 1 or higher the open of /dev/kmem will fail. FILES
/etc/dtab device table /unix /dev/kmem SEE ALSO
ucall(2), nlist(3), dtab(5) 3rd Berkeley Distribution December 30, 1992 AUTOCONFIG(8)

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LP(4)							     Kernel Interfaces Manual							     LP(4)

NAME
lp - line printer SYNOPSIS
/sys/conf/SYSTEM: NLP lp_printers # Line Printer LP_MAXCOL 132 # Maximum number of columns on line printers /etc/dtab: #Name Unit# Addr Vector Br Handler(s) # Comments lp ? 177514 200 4 lpintr # lp-11 line printer major device number(s): raw: 5 minor device encoding: bit 01 specifies 64-character set (instead of 96-character set) bits 06 are reserved bits 0370 specify line printer unit: <lp_unit> * 8 DESCRIPTION
Lp provides the interface to any of the standard DEC line printers on an LP-11 parallel interface. When it is opened or closed, a suitable number of page ejects is generated. Bytes written are printed. The unit number of the printer is specified by the minor device after removing the low 3 bits, which act as per-device parameters. Cur- rently only the lowest of the low three bits is interpreted: if it is set, the device is treated as having a 64-character set, rather than a full 96-character set. In the resulting half-ASCII mode, lower case letters are turned into upper case and certain characters are escaped according to the following table: { ( } ) ` ' | ! ~ ^ The driver correctly interprets carriage returns, backspaces, tabs, and form feeds. Lines longer than the maximum page width are trun- cated. The page width is specified via the LP_MAXCOL definition, set to 132 in the GENERIC distribution. FILES
/dev/lp /dev/MAKEDEV script to create special files /dev/MAKEDEV.local script to localize special files SEE ALSO
lpr(1), dtab(5), autoconfig(8) DIAGNOSTICS
None. BUGS
Although the driver supports multiple printers this has never been tried. 3rd Berkeley Distribution January 28, 1988 LP(4)

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