Hi Eric! Thanks for your hints!
2009/7/10 Eric Auer <[email protected]>: >> It's a paranormal phenomenon. The most strange part of the whole >> story, that my code succeeds in the following situations: > >> - When booted in WMVare or QEMU. >> - When booted on a real machine, via GRUB4DOS. >> - When I debug the code in FreeDOS debug, it also succeeds. > > Your code seems to be a boot loader - running it in DEBUG > can be problematic as you might overwrite parts of DOS in > RAM... But no, the FreeDOS kernel does not protect you from > crossing DMA boundaries via int 13... It only helps you by > never crossing DMA boundaries for file access, even if you > ask the kernel to transfer data from/to a buffer which is > around a DMA boundary :-). Indeed. When I was debugging the boot loader in FreeDOS debug, I adjusted the segment values to avoid overwriting the FreeDOS kernel. For example, I read to address 5000h:0000h instead of 07F0h:0000h. The strange thing: this address (50000h) obviously crosses the 64K physical address boundary, but it worked anyway. :S > True. Actually quite a few BIOSes / controllers have no > DMA boundary problem, but "real floppy" probably does. > You can also try how BIOS-supported USB drives behave. Unfortunately, I don't have a machine that is able to boot from a USB drive. :( > Let me know when you find out what causes your problem :-) With the help of a guy on the forum, I've figured out the problem. Here's what caused the phenomenon: http://board.flatassembler.net/topic.php?p=97464#97464 As you said, I crossed a boundary in a way I didn't notice. :) MegaBrutal ------------------------------------------------------------------------------ Enter the BlackBerry Developer Challenge This is your chance to win up to $100,000 in prizes! For a limited time, vendors submitting new applications to BlackBerry App World(TM) will have the opportunity to enter the BlackBerry Developer Challenge. See full prize details at: http://p.sf.net/sfu/Challenge _______________________________________________ Freedos-user mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freedos-user
