Ignore:
Timestamp:
Apr 3, 2013, 4:12:34 PM (11 years ago)
Author:
aitotat@…
google:author:
aitotat@gmail.com
Message:

Changes to XTIDE Universal BIOS:

  • P-Cylinders returned by AH=48h are now calculated from L-CHS capacity when RESERVE_DIAGNOSTIC_CYLINDER is defined.
  • Total sector count returned by AH=48h is now always P-Cylinders * P-Heads * P-Sectors per track for drives with less than or equal 15,482,880 LBA sectors.
File:
1 edited

Legend:

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  • trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/EBIOS/AH48h_GetExtendedDriveParameters.asm

    r530 r533  
    2323;--------------------------------------------------------------------
    2424; Int 13h function AH=48h, Get Extended Drive Parameters.
     25;
     26; It is not completely clear what this function should return as total sector count in some cases.
     27; What is certain is that:
     28; A) Phoenix Enhanced Disk Drive Specification v3.0 says that P-CHS values
     29;    are never returned for drives with more than 15,482,880 sectors (16384*15*63).
     30;    For those drives we can simply return total sector count from
     31;    ATA ID WORDs 60 and 61 (LBA28) or WORDs 100-103 (LBA48).
     32; B) IBM PC DOS 7.1 fdisk32 displays warning message if P-CHS values multiplied
     33;    together are different than total sector count. Therefore for drives with less
     34;    than or equal 15,482,880 sectors we MUST NOT return total sector count from
     35;    ATA ID WORDs 60 and 61.
     36;
     37;    Lets take an example. 6 GB Hitachi microdrive reports following values in ATA ID:
     38;    Sector count from WORDs 60 and 61  : 12,000,556
     39;    Cylinders                          : 11905
     40;    Heads                              :    16
     41;    Sectors per track                  :    63
     42;
     43;    When multiplying C*H*S we get      : 12,000,240
     44;    So the CHS size is a little bit less than LBA size. But we must use
     45;    the smaller value since C*H*S must equal total sector count!
     46;
     47; Now we get to the uncertain area where I could not find any information.
     48; Award BIOS from 1997 Pentium motherboard returns following values:
     49;    AH=08h L-CHS:   745, 255, 63 (exactly the same as what we return)
     50;    => Total Sector Count:       745*255*63 = 11,968,425
     51;    AH=48h P-CHS: 11873,  16, 63
     52;    AH=48h Total Sector Count: 11873* 16*63 = 11,967,984
     53;
     54; Notice how AH=48h returns lesser total sector count than AH=8h! The only
     55; way I could think of to get 11873 cylinders is to divide AH=08h sector
     56; count with P-CHS heads and sectors: (745*255*63) / (16*63) = 11873
     57;
     58; I have no idea what is the reasoning behind it but at least there is one
     59; BIOS that does just that.
     60;
     61; Since I don't have any better knowledge, I decided that when RESERVE_DIAGNOSTIC_CYLINDER
     62; is defined, we do what the Award BIOS does. When it is not defined, we multiply
     63; P-CHS values together and use that as total sector count.
     64;
    2565;
    2666; AH48h_GetExtendedDriveParameters
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