DOSFS problems

Adriano Verardo a.verardo at
Mon Mar 8 20:09:44 UTC 2004

Hello, Thomas.
thank you very much for the reply

Thomas Doerfler wrote:

>Hello Adriano,
>can you post more information about your 
>environment? What RTEMS version are you using, 
>what are the sizes of your harddisk paritions, 
>what type of FAT file system do you have there?
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.

>How do you try to mount the file systems?
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.
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.
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 ?

>I have adapted the RTEMS DOS-FS to pc386 and 
>MPC860 hardware, fed my changes back to RTEMS 
>(they are in 4.6.0 now), and finally had the 
>impression that things are running fine now. 
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 ?


>	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-

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