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at                        Device Driver                        at




Drivers for hard-disk partitions


/dev/at* are the COHERENT system's AT devices for the hard-disk's
partitions.  Each device  is assigned major-device number 11, and
may be accessed as a block- or character-special device.

The at  hard-disk driver handles two drives with  up to four par-
titions each.  Minor  devices 0 through 3 identify the partitions
on drive 0.  Minor devices 4 through 7 identify the partitions on
drive  1.  Minor  device 128  allows  access to  all of  drive 0.
Minor device 129 allows access to  all of drive 1.  To modify the
offsets and sizes of the partitions, use the command fdisk on the
special device for each drive (minor devices 128 and 129).

To access a  disk partition through COHERENT, directory /dev must
contain a  device file that  has the appropriate  type, major and
minor device numbers,  and permissions.  To create a special file
for this device, invoke the command mknod as follows:


/etc/mknod /dev/at0a b 11   0 ; : drive 0, partition 0
/etc/mknod /dev/at0b b 11   1 ; : drive 0, partition 1
/etc/mknod /dev/at0c b 11   2 ; : drive 0, partition 2
/etc/mknod /dev/at0d b 11   3 ; : drive 0, partition 3
/etc/mknod /dev/at0x b 11 128 ; : drive 0, partition table


***** Drive Characteristics *****

To read the characteristics of a hard disk, use the call to ioctl
of the following form:


        #include <sys/hdioctl.h>
        hdparm_t hdparms;
                . . .
        ioctl(fd, HDGETA, (char *)&hdparms);


where  fd is  a  file descriptor  for  the hard  disk device  and
hdparms receives the disk characteristics.

***** Non-Standard and Unsupported Types of Drives *****

Prior releases of the  the COHERENT at hard-disk driver would not
support disk drives whose  geometry was not supported by the BIOS
disk  parameter tables.   COHERENT release  3.1 adds  support for
these  drives  during   installation  by  ``patching''  the  disk
parameters into the bootstrap and the /coherent image on the hard
disk.  Please note that if  you intend to move your COHERENT root
file system from an  unsupported drive to another disk drive, you
will need  to patch these parameters to  match the drive geometry
of the new disk drive.


COHERENT Lexicon                                           Page 1




at                        Device Driver                        at




***** Files *****

/ddeevv/aatt* -- Block-special files
/ddeevv/rraatt* -- Character-special files

***** See Also *****

device drivers, fdisk
















































COHERENT Lexicon                                           Page 2

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