DOSFS problems

Thomas Doerfler Thomas.Doerfler at
Mon Mar 8 21:25:04 UTC 2004

Hello Adriano,

> RTEMS 4.6.0, several HDs, variuos brands, from 120M to 6G.
> All formatted and made bootable with DOS 5.0 and 6.22
> Always one partition.  Tried with maximum possible size and smaller sizes.
> Same results with all combinations.

I would guess that having a 6G partition under DOS 5.0 or DOS 
6.22 is impossible, so I think the maimum partition size would 
be 512 MByte, right?

> With the "fileio" example and other simple tests i "copied" from it.
> Really, with one 120MB HD, the mount and read/write file
> operations succedeed but the files written by DOS were not visible to RTEMS
> and vice versa.

One hint: Long filenames are not supported by RTEMS...

> On that - OLD AND USED AS IS = Not reformatted -
> HD the BPB was (partially ?) reasonable (512 byte/sect etc)
> and very different from those of the other - DOS REFORMATTED - disks.

Could you possible give the values that are present in your 
MBR and partition table? It may be that the RTEMS DOSFS code 
does not implement ALL possible partition types and options.

> And more, the good disk doesn't work anymore after a DOS 6.22/5.0 reformat !
> So i deduced that the problem is the initialization of the BPB made by DOS.
> Is it correct ?

Yes, this would be my first idea. 
> I'm sure that the problem is something wrong here, not in RTEMS.
> Are there particular requirements about the PC motherboard/motherboard 
> setup/disks/disk interface ?
> Is it possible that DOS goes wrong due to a hw config mistake ?

do you have a special harddisk manager installed under DOS, to 
access more than 512 MBytes? Maybe this breaks it, because 
these managers used to recode the sector addressing scheme, as 
I recall...


> Adriano
> >wkr,
> >	Thomas.
> >
> >  
> >
> >>Hi, all
> >>I'm trying to mount the primary master HD on a PC motherboard 
> >>(BSP=pc386) but the operation fails with all disks I connect. All of 
> >>them are DOS-formatted. Using different mix DOS versions/HD model 
> >>doesn't solve the problem.
> >>
> >>Tracking the code I see that RTEMS uses the BPB within the MBR but finds 
> >>wrong data.
> >>I verify also that RTEMS always reads the data effectively on the HD, so 
> >>the problem seems to be the initialization of the HD. Correct ?
> >>
> >>If yes, can anyone kindly explain to me how to initialize it ?
> >>Thank you in advance.
> >>
> >>A. Verardo
> >>    
> >>
> >
> >--------------------------------------------
> >IMD Ingenieurbuero fuer Microcomputertechnik
> >Thomas Doerfler           Herbststrasse 8
> >D-82178 Puchheim          Germany
> >email:    Thomas.Doerfler at
> >PGP public key available at: http://www.imd-
> >
> >
> >
> >  
> >

IMD Ingenieurbuero fuer Microcomputertechnik
Thomas Doerfler           Herbststrasse 8
D-82178 Puchheim          Germany
email:    Thomas.Doerfler at
PGP public key available at: http://www.imd-

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