Date: Sat, 6 Jan 1996 13:15:22 +0200 From: Dmitry Kohmanyuk <dk@dog.farm.org> To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch) Cc: freebsd-hackers@freebsd.org Subject: Re: HELP!!! THIS IS AN EMERGENCY (fwd) Message-ID: <199601061115.NAA12788@dog>
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In article <inj.4-30ec46df-3893@bee.cs.kiev.ua> you wrote:
> > c = 10 bits = 2^10 = 1024. Not 65536.
> This is the BIOS-visible part. BSD can go beyond this, even for disks
> where the first part must be accessible to the BIOS (like boot disks).
ooh, but when I have >=1024 c disk with non-BSD occupying the first part
of it, I still _cannot_ boot BSD without installing some lame s/w like
diskmanager (which I hate to use and don't have anyway - and I have LBA
drive and LBA IDE controller).
Or is there LBA support in the works?
Or should I still answer "no" to people with big drives asking can FreeBSD
do the same as OS/2 (e.g.) does?
> No. Register 0x1f6 does only use bits 0 through 3 for head addressing
> (16 heads), bit 4 selects the primary/secondary drive, bits 5/6 select
> the sector size, bit 7 is used for ECC usage. (van Gilluwe, p 525).
> Both are irrelevant for us, since they belong to DOS.
> The INT 0x13 interface traditionally used 10 bits for cylinder
> numbers, and an entire byte for head numbers, though the hardware
> registers limit the head number to 0..15.
hmm, not so precisely. Any AWARD or AMI BIOS since '93 (or '94?) supports
the 12-bit cylinder addressing. Read Ralf Brown's Interrupt List for details.
or I would just quote it here:
--------B-1302-------------------------------
INT 13 - DISK - READ SECTOR(S) INTO MEMORY
AH = 02h
AL = number of sectors to read (must be nonzero)
CH = low eight bits of cylinder number
CL = sector number 1-63 (bits 0-5)
high two bits of cylinder (bits 6-7, hard disk only)
DH = head number
DL = drive number (bit 7 set for hard disk)
ES:BX -> data buffer
Return: CF set on error
if AH = 11h (corrected ECC error), AL = burst length
CF clear if successful
AH = status (see #0138)
AL = number of sectors transferred
Notes: errors on a floppy may be due to the motor failing to spin up quickly
enough; the read should be retried at least three times, resetting
the disk with AH=00h between attempts
the IBM AT BIOS and many other BIOSes use only the low four bits of
DH (head number) since the WD-1003 controller which is the standard
AT controller (and the controller that IDE emulates) only supports
16 heads
AWARD AT BIOS and AMI 386sx BIOS have been extended to handle more
than 1024 cylinders by placing bits 10 and 11 of the cylinder number
into bits 6 and 7 of DH
SeeAlso: AH=03h,AH=0Ah,AH=06h"V10DISK.SYS",AH=21h"PS/1"
-
> van Gilluwe claims that the topmost two bits of %dh could be used as
> an extended cylinder number. Dunno which BIOSes support this.
--
"Emacs is a fine O/S, but I still prefer UNIX."
- Tom Christiansen
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