Download Coherent Device Driver Kit

60
at
To access a disk partition through COHERENT, directory l dev must contain a device me that has
the appropriate type. major and minor device numbers , and permissions . To create a special me
for this device, invoke the command mknod as follows :
/etc /mknod
/etc /mknod
/etc /mknod
/etc lmknod
/etc/mknod
/dev/at Oa
/dev/at Ob
/dev/at Oc
/dev/at Od
/dev/at Ox
b
b
b
b
b
0
11
1
11
2
11
3
11
1 1 12 8
1
1
1
1
1
drive
drive
drive
drive
drive
o,
o,
o,
o,
o,
partition
partition
partition
partition
partition
0
1
2
3
table
Drive Characteristics
When processing BIOS 1/0 requests prior to booting COHERENT, many IDE drives use
''translation-mode" drive parameters: number of heads , cylinders, and sectors per track. These
numbers are called translation-mode parameters because they do not reflect true physical drive
geometry. The translation-mode parameters used by the BIOS code present on your host adapter
can be obtained using the dpb utility found on the boot diskette of versions 3 .2 .0 and later of
COHERENT. It is often necessary to patch the at driver with BIOS values of translation-mode
parameters in order to boot COHERENT on IDE hard drives . In COHERENT versions 3 . 1 .0 and
later, drive parameters are stored in table atparm_ in the driver. For the first hard drive, number
of cylinders is a two-byte value at atparm_+0, number of heads is a single byte at atparm_+2 . and
number of sectors per track is a single byte at atparm_+ l 4. For the second hard drive, number of
cylinders is a two-byte value at atparm_+ l 6 , number of heads is a single byte at atparm_+ l 8 , and
number of sectors per track is a single byte at atparm_+30. For example, if testcoh is a kernel
linked with the at driver and you want to patch it for a second hard drive with 829 cylinders, 1 0
heads, and 2 6 sectors per track. you can do
/con f/patch testcoh atparm_+ 1 6 =8 2 9 atparm_+l 8=l 0 1 c atparm_+3 0=2 6 1 c
To read the characteristics of a hard disk once the at driver is running, use the call to loctl of the
following form:
#inc lude <sys /hdioct l . h>
hdparm_t hdparms �
ioct l ( fd , BDGETA , ( char * ) & hdparms ) �
wherefd is a me 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 adds support for
these drives during installation by "patching" the disk parameters into the bootstrap and the
I coherent image on the hard disk.
Files
I devI at• - Block-special rues
l devlrat• - Character-special ffies
See Also
device drivers, fdisk
LEXICON