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Mail Archives: djgpp/2002/04/21/13:15:22.1

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From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Loading boot sector to memory
Organization: Systematic Software
Message-ID: <ccs5custb57ibq4c3h4vtlshkqkecf2llm@4ax.com>
References: <a9umfc$rgq3 AT imsp212 DOT netvigator DOT com> <a9umpo$rgl3 AT imsp212 DOT netvigator DOT com>
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Date: Sun, 21 Apr 2002 17:08:47 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

On Sun, 21 Apr 2002 23:40:16 +0800, "Jacky Luk"
<luckie AT netvigator DOT com> wrote:
>"Jacky Luk" <luckie AT netvigator DOT com> glsD
>:a9umfc$rgq3 AT imsp212 DOT netvigator DOT com...
>> 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 #00234)
>>  AL = number of sectors transferred (only valid if CF set for some
>>        BIOSes)
>> 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
>>  most BIOSes support "multitrack" reads, where the value in AL
>>    exceeds the number of sectors remaining on the track, in which
>>    case any additional sectors are read beginning at sector 1 on
>>    the following head in the same cylinder; the MSDOS CONFIG.SYS command
>>    MULTITRACK (or the Novell DOS DEBLOCK=) can be used to force DOS to
>>    split disk accesses which would wrap across a track boundary into two
>>    separate calls
>>  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
>>  under Windows95, a volume must be locked (see INT 21/AX=440Dh/CX=084Bh)
>>    in order to perform direct accesses such as INT 13h reads and writes
>>  all versions of MS-DOS (including v7 [Win95]) have a bug which prevents
>>    booting on hard disks with 256 heads, so many modern BIOSes provide
>>    mappings with at most 255 heads
>> SeeAlso: AH=03h,AH=0Ah,AH=06h"V10DISK.SYS",AH=21h"PS/1",AH=42h"IBM"
>> SeeAlso: INT 21/AX=440Dh/CX=084Bh,INT 4D/AH=02h
>>
>> According to the above, how do you setup the registers for loading boot
>> sector to memory (GAS or GCC)?
>boot sector of hard disk C:
zeros in all args except # sectors AL and high bit of drive # DL

-- 

Thanks. Take care, Brian Inglis 	Calgary, Alberta, Canada

Brian DOT Inglis AT CSi DOT com 	(Brian dot Inglis at SystematicSw dot ab dot ca)
    fake address		use address above to reply

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